Eindhoven University of Technology

MASTER

An experimental evaluation of (1) the manual and (2) the ease of operating the DC 685 carcassette receiver under a simulation of traffic conditions

Fleurbaay, E.R.

Award date:1990

Awarding institution:Utrecht University

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Institute for Perception Research PO Box 513, 5600 MB Eindhoven

Rapport no. 740

An experimental evaluation of (1) the manual and (2) the ease of oparating the DC 685 car cassette receiver under a simulation of traffic conditions

E.R. Fleurbaay

17.04.1990

An experimental evaluation of (~) the manual and (2) the ease of eperating the DC 685 ·car cassette receiver under a simulation of traffic conditions.

Utrecht, 27 March 1990 Report of a research project at the IPO (Institute for Perception Research) in partial fulfillment for a Masters deqree in Psycholoqy, under the responsibility of:

Prof. dr. ir. F.L. van Nes (IPO) Drs. H.J.G. Zwaqa (Rijks Universiteit Utrecht)

By: Eric Fleurbaay

BXecutive summary

This report describes the methode of research as well as the results of two experiment& in which the ease of use of the manual as well as the ease of oparating the DC685 cassette receiver were evaluated.

In Experiment I the existing instructien manual was evaluated in an experimental setting with six subjecte. The subjecte performed a number of tasks with the manual as their only means of information. The subjecte were asked to 'think aloud', while attempting to locate needed information. The utterances~of the subjects were recorded in order to locate trouble spots in the manual. Next, the manual was evaluated from a theoretica! point of view, by means of a walk-through check.

The results of Experiment I indicate the need for altering the structure of the existing manual. Next, the content of a number of sections should be supplemented, shortened or changed. Suggestions are made for additions and changes.

In Experiment II the ease of oparating the DC685 cassette receiver was evaluated under a simulation of traffic conditions. As in driving a car, the attention of the subjecte was primarily focuseed on a visual task. Moreover, as in driving a car, the subjecte had to react quickly and adequately to this visual task. Six well trained subjecte performed a number of radio control tasks in a Single and Dual task condition. In the Dual Task condition, the subjecte performed a visual reaction time task as well. The performance of this reaction time task had priority. In both experimental conditions the time, needed to perform the radio control tasks, was measured.

The results of Experiment II indicate that the tasks for which the subjecte had to look at the display of the car radio were affected most by the Dual Task condition. Next, the number of oparation steps that constituted the radio control tasks had an effect on the speed with which the task is performed. The more oparation steps, the more the oparation speed is slowed down. Finally, it seems that doubling the number of operatien steps in an oparation sequence results in an oparation time that is more than doubled.

Table of Contents

EXPERIMENT I

1. Summary of Experiment I 1

2 • Introduetion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11

Reading instructions •••••••••••.•••.••••••••••••••.•••••••••••. Searching for information ••••••••••••••••••••••••••••••••••.••. Understanding ••••••••.•••••••.••.••••.••••.•.•••••••••••.•••••• Applying the knowledqe ••••.•.•••.•.•••••.••••••.•••••••.•.••••• Oesigning and testing instructions ••••••••••••••••••••••••••••• Analysis ...................................................... . The planning phase ............................................ The development phase .•••••••.••.••••••.••••••••••.•••.••..•••• The evaluation phase •..•..•....•.•••••.••••••••••.••.••••••.••. Methods for evaluating document design ••••••••••••••••••••••••• Evaluation of the PHILIPS oe 685 cassette receiver instructions •••••.•••.•••.•••••••••••••.•••.•••••

2 2 3 4 5 5 5 6 6 7

9

3. Method of research •••.•••.••••••.••.••••••••.••..•..•••.•••.•.•.••..•• lO

3.1 3.2 3.3

General .•..•.••..••..•...•..........•..•.........•..•...•...... 10 Subjects .••...•••..•...•...•......•••...•.•...•..•••..••.....• • 10 Material .........•......•...................................... 11

4. Results ............................................................... 12

4.1

4.2

The results of the protocol analysis ••••••••••••••••••••••••••• 12

4.1.1 4.1.2

4.1.3

The information that was searched for ••••••••••••••••••• 17 Correct and incorrect actions performed by the subjects ••.•••.•••..••••••.••••..••••..••••••••••••• 22 Assumptions of the subjecte regarding the working principlesof the car radio ••••••••••••••••••••••••••••• 23

The registrations made by the remote computer •••••••••••••••••• 23-

4.2.1 4.2.2 4.2.3 4.2.4

Performance of the subjects ••••••••••••••••••••••••••••• 23 Oeduced incorrect assumptions ••••••••••••••••••••••••••• 33 Errors that were made by the subjects ••••••••••••••••••• 33 Amount of time needed for completing the scenarios and reading the instructions •••••••••••••••••••••••••••• 34

Table of Contents

s. Discussion and conclusions •••••••••••••••••••••••••••••••••••••••••••• 35

5.1 5.2 5.3

5.4

General •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 35 The overall structure of the instructions •••••••••••••••••••••• 35 Alteratiens •••••••••••••••••••••••••••••••••••••••••••••••••••• 35

5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 5.3.6 5.3.7 5.3.8

The aection "Algemean" •••••••••••••••••••••••••••••••••• 41 Adjustment of the sound functions ••••••••••••••••••••••• 42 The section "Aan/uit- Volume" •••••••••••••••••••••••••• 43 The section "Instellen van de geluidsfuncties" •••••••••• 44 The sectien eLoudness" •••••••••••••••••••••••••••••••••• 45 The sectien "Automatisch afstemmen" ••••••••••••••••••••• 45 The section "Bandafstemming" •••••••••••••••••••••••••••• 46 The section "Voorkeuzetoetsen" •••••••••••••••••••••••••• 47

5.3.9 The section "Automatisch programmeren" •••••••••••••••••• 48 5.3.10 The section "Programmeren met Autostore" •••••••••••••••• 48

Namesof knobs and functions ••••••••••••••••••••••••••••••••••• 49

EXPERIMENT II

6. Summary of Experiment II •••••••••••••••••••••••••••••••••••••••••••••• Sl

7. Metbod of resaarch •••••••••••••••••••••••••••••••••••••••••••••••••••• 52

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9

Introduction ••••••••••••••••••••••••••••••••••••••••••••••••• 52 The secondary task technique ••••••••••••••••••••••••••••••••• S2 The experimental conditions •••••••••••••••••••••••••••••••••• 53 The training, given to the subjects •••••••••••••••••••••••••• S4 The Radio Saingle Taak condition ••••••••••••••••••••••••••••• 60 The Reaction Time Single Taak condition •••••••••••••••••••••• 61 The Radio Dual Task condition •••••••••••••••••••••••••••••••• 63 Subjecte ........................................................... 64 Material •••••••••••••••••••••••••••••••••• : •••••••••••••••••• 64

8. Results and discussion •••••••••••••••••••••••••••••••••••••••••••••••• 65

8.1 8.2 8.3

8.4 8.5

General •••••••••••••••••••••••••••••••••••••••••••••••••••••• 65 The reaction time meaaures ••••••••••••••••••••••••••••••••••• 65 The resulta of the Radio Single Task and Radio Dual TAsk condition •••••••••••••••••••••••••••••••••••• 66 Task-parts ••••••••••••••••••••••••••••••••••••••••••••••••••• 69 Task-part analyses ••••••••••••••••••••••••••••••••••••••••••• 70

8.5.1 Remote box racerding problema, due to varying search times of Automatic Tuning •••••••••••••••••••••••••••••• 71

8.5.2 Assumptions regarding the operatien of the sound function and the preset function ••••••••••••••••••••••• 71

Table of Contents

8.6 The Task-part analyses ••••.•••••.•••...•••••••..•.••.•.••..•••..••• 72

8.6.1 Analysis of the task-part: P-Loud •••••..•••.••..••••.•••.•.• 72 8.6.2 Analyais of the task-part: Ast-P ........•.....••..••.•..•..• 74 8.6.3 Analysis of the taak-part: s.Functions-Large knob 4-- ••••••• 76 8.6.4 Analysis of the taak-part: s.Functions-Large knob -o- ..•.... 78 8.6.5 Analysia of the taak-part: P-S.Functions-Large knob 4-- •••• 80 8.6.6 Analysis of the taak-part: P-S.Functions-Large knob -0- •••• 82 8.6.7 Analyais of the taak-part: Band-S.Functions-Large knob 4-- .84 8.6.8 Analysis of the taak-part: Band-S.Functions-Large knob -0- .86

8.7 Unexpected system characteriatics. of the oe 685 car radio ••••••••• 88

8.7.1 8.7.2

Differential search time of the function Automatic Tuning ••• 88 Difficulties in the Autostore Oparation mode •••••••••••••••• 88

8.8 The performance of the radio control tasks •••••••••••••••••••••••• 90

9. Conclusions ....•...•.... .........•.................................... 91

9.1 The performance of the Teaction Time Task ••••••••••••••••••••••••• 91 9.2 Performance of the Task-parts ••••••••••••••••••••••••••••••••••••• 91

9.2.1 The extent to which the Task-parts were affected by the Dual Task condition •••••••••••••••••••••••••••••••••• 9l

9.2.2 Number of operation steps of the Task-parts ••••••••••••••••• 93 9.2.3 Possible effects of the length of the original

radio control taskon the performance of the task-parts ••••• 93

9.3 The eperation of the function Automatic Tuning •••••••••••••••••••• 95 9.4 The eperation of the Loudness function •••••••••••••••••••••••••••• 95

Raferences ....•.......................................................... 96

EXPERIMENT I

1. Summ.ary of Experiment I

In Experiment I the existing instructions of the DC685 car radio were evaluated. Six subjecte were asked to perferm a number of tasks with the instructions as their only means of information. The subjects were asked to • think aloud • dur ing their attempts to perferm the tasks. The utterances, that were recorded, were analyzed in order to locate the trouble spots in the instructions. Next, the instructions were examined from a theoretica! view point, by means of a •walk through check'. The results of the experiment as wellas the results of the •walkthrough check' indicate the need fora number of alterations.

The overall structure of the instructions should be altered, since the existing structure does not guide the reader adequately through the bulk of information. Ideally, the structure of the instructions must facilitate the search process of the reader. The suggested, altered, structure can be applied not only to the instructions of the oe 685 but also to the instructions of ether Philips car radios that have certain features in common with the DC 685.

Also, the content of a number of sections should either be altered or supple­mented with new information. In most cases suggestions for additions or changes are made. The text also contains a number of printing errors that should be corrected. In some instanoes the information was factually wrong. This was for instanee the case in the sectien that contained information concerning the Autostore function; the most difficult sectien of the instructions. Finally, the text contained more than one name for some functions and knobs. If the ease of use is to be enhanced, each knob or function must be referred to with one name.

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2. Introduetion

2.1 General

Nowa.days most consumer product& are a.ccompa.nied by instructions. These instructions are either printed on the package (e.g. for household a.rticles, a.erosols, dornestic applia.nces) or given as separate lea.flets or booklets (e.g. for computer hard- and software, audio equipment). These instructions are aimed at explaining the working principle& of the product to the consumer, or at helping the customer a.ssemble the various parts of a purebaeed 'do it yourself' artiele (e.g. 'do it yourself furniture', 'd.i.y. kits'). Technologica.l developments have made many of these, often fa.miliar, products very sophisticated. This sophistica.tion will continue a.lthough there might be a limiting factor. 'l'he limiting factor on such developments will not be the technoloqy but the a.bility to explain to the customer how to make full use of the product and its fa.cilities (Wright, 1981). Yet, ma.nufa.cturers have to reaort to printed instructions as their only means of providing the information to the customer. or, as Szlichinsky (1979) statee it; "Instructions: a necessary evil". Sometimes the essentia.l information and knowledge, needed to opera.te the device correctly, can be so complex that written instructions may beoome incomprehensible. For that reason special training courses are given to those who bought, e.g., a knitting machine or, in genera!, professional equipment (e.g. medica.! equipment, computer hard- and software).

'l'he design of applia.nces in such a. wa.y tha.t their opera.tion follows directly from their design is, in principle, possible. Such a device will be self-expla.natory. However, the device ma.y beoome impractica.ble beca.use of its complexity.

2.2 Readinq instructions

'l'here are some actlvities readers have in common while reading instructions. These common actlvities are:

• Sea.rching for informa.tion: readers have to find the information which is relevant to their needs.

• Onderstanding the information: readers have to comprehend the presented informa.tion.

• Applying the ga.ined knowledge: readers have to implement their understa.nding.

2.3 Searchinq for information

It is a well-known fa.ct that instructions are often rea.d superficially, if read at all. 'l'his also applies to formfilling where instructions are not a.lwayl!' followed (Wright, 1984) , and in reading tables where the descriptions are not a.lwa.ys read (Wright a.nd Threlfall, 1982).

Explana.tions for this beha.vior va.ry from indolence and a.pathy to baste and time pressure. Roseon (1986) cites a. fa.miliar example of a motiva.ted user who is so positively motivated to get the job done that he feels he ca.n not afford the time to learn about fa.cilities that would help him to do it. Ma.ck, Lew is and Carroll ( 1983) found tha.t readers often beoome impatient

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with lengthy manuals and strike off to follow their own direction. However, as Wright, creighton and Tbrelfall (1982) suggest, there is another reaeon why people ignore instructions, namely the expectations they have regarding the appliance. Users may think there is nothing new they need to know about the appliance and therefore do not bother to read the instructions. Users may come to the conclusion, however, that they do need certain information, but often think that there are quicker or easier ways of finding out, than reading the instructions. Users might, for instance, prefer to play with the appliance, or prefer to aak someone else. To save further time, in most cases readers turn to the instructions, after their initia! attempts turned out to be unsuccessful. Nevertheless, after one unsuccessful trial readers may think, rightly or not, that they know what went wrong and try again (Szlichinsky,l979).

If people are presented a list with a number of products and are asked how much of the instructions, accompanying the products, they would read, there will be a considerable agreement regarding the instructions that will not be read (Wright, 1984). It seems that not reading the instructions is a conscious choice rather than a careleas mistake. In order to search for information, readers have to formulate a target to look for, although they somatimes do not formulate such a target. In other words, instructions are only raad if the customer has questions that need to be answered. An implication of this fact is that needed information must be found quickly and easily. Therefore, the instructions should provide means of helping the readers to find the answers to questions they might have about the product. Providing lists of contente, indexes, page headings and section headings can facilitate this searching process at a macro-level. Page-labels in the margin of each page, containing section headings, can be very useful, since readers often prefer to leaf through a booklet. At a micro-level there are numerous components that contribute to the legibility and usability of the instructions (e.g. typographically distinguished levels of subheadings within the pages). Felkar (1980) gives a review regarding these micro-level guidelines.

Apparently, the reading behavior is not as straightforward and predictable, as one might think. This is more or leas reflected in the .. change of view that has taken place during the last ten years, concerning the content of instructions. The traditional view emphasized completeness and explicity of the instructions, providing detailed explanations of every relevant issue (Charney, 1986). Black1 Carroll and McGuigan (1987), however, advocate a minimalistic approach in which, among other things, all the verbiage is slashed and focus is on tasks that are ordinarily done rather than explaining the system as a whole.

2.4 Onderstanding

It is important to differentiate two kinds of understanding in reading instructions. on the one hand, readers may fail to understand what the writer means (declarative knowledge). on the other hand, readers may have difficulties in implementing their knowledge (procedural knowledge). Both kinds of problems may arise with text and pictures.

The form in which the information is presented has implicationa for the way in which it is remembered. Readers who study a recipe written as a prose

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paragraph tend to reproduce it as prose. Similarly, when this information is given as a formatted list of instructions, people tend to reproduce that format (Hartley, 1982).

There is much evidence for the idea that readers try to integrate the information with knowledge they already have (Huckin, 1983 and Norman, 1983). On the basis of former experiences, conceptual networks, so called schemata, are formed actively. These schemata are stored in l~ng term memory and form a frame for the way we perceive and understand the world around us. Bverything that helps the reader to activate the proper and earlier-obtained knowledge will help to understand new information. The schemata generate expectations that can prove to be correct. For instance: readers have experiences with language and texts and will have expectations regarding the structure of documents. However, it is possible that the reader haa incorrect schemata that, subaequently, will genera te incorrect expectations. This may be the case, for instanee, in trying to opera te an appliance that resembles a familiar one, but differs on some erucial aspeets. Here the expeetations prove to be incorrect.

In three experiments Kieras and Bovair (1984) have investigated the role of a mental model in learning to operate a new device. With a mental model they mean a sort of understanding of the werking principles of the appliance, in terms of its internal structure and processes. The experiment• showed that a mental model ean facilitate learning, execution and reeall of the operatien instructions. The experiments also showed that a mental model can facilitate inferences regarding the werking prineiples and operation.

Black, Carroll and McGuigan {1987) have tested four types of instructions for a word processor and investigated what kind of minimal instruetions would be most effective. The best results were obtained with an Inferential Manual. In this Inferential Manual the information was presented in such a way that the reader eould make inferences with regard to the computer system, rather than being told explicitly what to do. The subjecte that used this type of instructien manual not only learned the normal operations, but also learned a number of general concepts about the system. In other words, they developed a mental model of the computer system.

2.5 Applyinq the knowledqe

one might think that, after presenting the information in a way that is easy to find and easy to comprehend, all problems are over. Yet, once the adequate information is found and understood, one or more actions have to beundertaken (e.g. to use a digital watch as a stopwatch). Lengthy action sequences are error-prone and it is possible that an error is detected only after the last action of the sequence is done, because in the end, something unexpected happens. Here, dividing the information into meaningful and numbered substages can be helpful. Furthermore, the reader may choose to read more than one procedural step at a time, instead of reading and applying the information step by step. As a result, errors may occur, because the memory demands are then too strong.

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2.6 Desiqninq and testinq instructions

Product documentation is recently brought into the sphere of quality control. Two important reasoos for this development are:

1. user-tested documentation reduces the number of consumer complaints, questions, service calls and maintenance costs for improperly handled products (Mills and Dye, 1985).

2. it is recognized that customer satisfaction is promoted if information can be found quickly and easily.

With regard to the metbod in which instructions can be designed, there are several views. Szlichinsky (1979) advocates an overall systems approach. The objective of this (genera!) approach is to bring an unexperienced operator up to the point where he can fully benefit from the product or appliance. A more detailed view is held by, for instance, Barnett (1979), Felker (1980), and Duffy (1981). They all advocate a design metbod containing a number of design steps, in which the complete design of the instructions is defined, including evaluation phases for further development. The latter all have very similar design steps: Analysis, Planning, Development and Evaluation.

2.7 Analysis

In the f irst design step the function of (e.g. raferenee volume, tutorial). characteristics like age, socio-economie defined next to (Wright, 1981):

the instructions is determined Likewise, relevant audience data or cultural aspects are

• what the customer needs to know about the product, • what the cuetoroer already knows about the product, • what the customer assumes about the product and,therefore, need not to be

told, • what wrong assumptions the cuetoroer might have, • what questions the customer has with regard to the product.

There is a variety of procedures one can call upon during the pre-design analysis to define the content of the instructions. Empirical data indicating what the customer already knows about the product can come from questionnaires or interviews. Individual interviews, in which potential customers interact with the product, can elicit spontaneously asked questions. All data gathered in this way can be of influence on the content and sequencing of the, new,instructions (Wright, 1981).

2.8 The planning phase

During the planning phase:

• the appropriate content of the instructions is determined, • the content is organized for the audience that will use the instructions, • relevant grapbics that help clarify the information are selected or

designed.

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The function of the instructions influences the form in which the instructien ought to be presented. If general outlinea are important a hierarchical structure is preferred. If details are of importance then a listing structure, explicitly defining all the steps and procedures, is to be recommended. For presenting the information one may choose either verbal instructions, or pictures, or a combination of both. Since the need for multilingual instructions bas increased, diagrams and pictorial illustrations are used more and more, since an incidental benefit of grapbics is the fact that they do not have to be translated for use in foreign markets. Unfortunately, many of the research findings on grapbic communication are ad hoc and do not build into a single theoretica! framewerk (Wright, 1981).

2.9 T~e development phase

In the development phase micro-level decisions are made by the writer. It is important to keep in mind what the readers are doing, while interacting with the instructions, to indicate where difficulties are likely to arise. Difficulties due to reader strategies or cognitive limitations can be located with feedback during a first evaluation. Wright (1981) auggeste to track down:

• cognitive resources such as perception and memory, • other resources, such as language and decision making,

that the reader calls upon while complying with the instructions.

Memory problems may arise in sequences of procedural steps. The instructions can be difficult to comprehend because of long and complex sentences. Sometimes the reader has to make decisions. For example, the instructions of battery-operated appliances often contain the advice to remov~ the batteries if the appliance will not be used for some time. Bere the reader has to decide how much time "some time" is (Wright, 1981). COnsequently, the taak analysis can uncover certain needs of the user, that the user bimself is not aware of. For instance: adequacy of content, struc­ture and presentation of the instructions.

2.10 The evaluation phase

One of the problems in evaluating instructions is the lack of obvious evaluation criteria. Hoping that none of the readers will experience difficulties in reading the instructions seems to be unrealistic. Yet, how many errors or troublespots can be tolerated? Wright (1984) suggests that the answer depende in part on the cost benefit of removing these trouble spots. Where patterne of errors are found, revision is likely to be worthwhile. The objective of this phase in the design metbod is not to reach perfection, but to avoid the errors and nonsense that can be found in instructions much too aften. To what extent the instructions are to be further developed also depënds on the importance of the instructions, for instanee as an index of quality, to the manufacturer.

Although the outline of the four stage design metbod seems to be a general one, Redish et al., as quoted in Wright (1981), emphasize the cyclic

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interactions between the four phases. 'l'he evaluation phase is not merely the f inal test of the instructions. By trackinq down the trouble spots, revisions can be made and evaluation of the revised instructions can be done aqain. 'l'he next section of this report contains a number of widely applied procedures used for evaluatinq document desiqn. Here the qeneral term documents is chosen, because the procedures can be applied not only to instructions, but also to other text formats.

2.11 Methods for evaluating document design

'l'he evaluation procedures can be loosely divided into two cateqories (Schumacher and Waller, 1985):

A) outcome measures: a completed document, or parts of a document, are tested.

B) Process measures: the interaction of the reader with the document is emphasized.

A. outcoae aeasures

Readability Generally, readability procedures measure two aspects of a document. On the one hand word characteristics, such as length and familiarity of the words, are defined. On the other hand the length of sentences is defined. After combininq both measures, a numerical estimate is obtained, that indicates the level of readinq skill a reader needs to comprehend a particular document. Readability measures have a number of advantaqes. 'l'he formulas are relatively easy to elaborate, low in cost and quickly obtained.

However, these measures provide information that is too qlobal. 'l'here are numerous factors that can contribute to the readability of a qiven document (goal of the reader, textual cohesion). Furthermore, the obtained data do not provide any information on how to revise an already existinq document.

Performance tests 'l'he typical approach in these tests has been to present a set of subjecte in a laboratory settinq, passages of materials manipulated on some particular text feature and then to assess the impact of this feature on a memory or comprehension task.

Performance tests have an important but limited role in document desiqn. 'l'his procedure is most useful in establishinq general principles of desiqn or desiqninq a document. Limitation: it is not possible to specify exactly how to redesiqn a document to make it more effective.

Structural analysis 'l'his procedure is qenerally aimed at specifyinq the nature and relationships of the various ideas presented in a text. Emphasis is on text content rather than on presentation. This analysis provides too little direct quidance as to how various structural properties influence comprehension and usability to be of main value in the design of a particular document.

7

User ratings User ratings provide a means of obtaining global impressions about a particular document by asking, for example, teachers to reapond to a questionnaire regarding a text. Similarly, the actual readers may be asked to give their opinion about the readability or effectiveness of a text or a document. These ratings suffer from a lack of reliability due to the small and possibly biased sample of respondente. The observations that are made are often at a general level and fail, therefore, to provide specific information on how to improve a text or document. Therefore, the user ratings are only helpful in making certain macro-level decisions, regarding content coverage and organization.

B. Process aeasures

User ed.its Inexperienced individuals are given a document, such as a technica! manual for a machine, and are asked to work with the manual as their only aid. Careful observations of pauses and errors can provide insight into document design problems or weaknesses in specific documents This procedure is quite time-consuming with each subject and the data are difficult to summarize.

Protocol analysis This procedure has become a prime tool in writing processes. Subjecte are asked to 'think aloud' as they attempt to understand a document or complete a form. This procedure produces a massive amount of information and attempts to analyze the comments in order to:

a) determine what problems are being generated for the reader, b) determine what general processas readers employ in trying to genera te

meaning from the text.

Problems may arise when there is more than one observer (bias in the observations).

8

2.12 Evaluation of the PHILIPS oe 685 cassette receiver instructions

As was mentioned earlier, there are numerous problems that can arise while readers comply with the instructions. If instructions are to be evaluated, it is very important to use an evaluation metbod that can reveal, e.q., what problems arise, what information is looked for and how the readers search for that information. In other words, the evaluation method should provide information on how to improve the existinq instructions. In order to meet this demand, the protocol analysis (see section 2.10) will be used to evaluate the PHILIPS DC 685 car-radio instructions. The qoal of this analysis is to locate possible trouble spots in the instructions of the Philips cassette receiver type oe 685. In order to locate these trouble spots two kinds of data will be qathered in an experiment.

1) Subjecte are asked to perform 6 different tasks on the car radio with the instructions as their only means. The subjecte are asked to think aloud while they sol ve a number of tasks. The utterances of the sub­jects will then be analyzed in the followinq way:

• What information is presented in the wronq sequence. • What information is factually wrong. • What information miqht be necessa.ry for the reader to develop a

mental model. • What information is verbiage and can be slashed. • How lonq does it take the subjects to perform the tasks and thus

learn about the functions concerned.

2) The existinq instructions will be examined using a •walk throuqh• check, in which from a theoretica! view ( see section 2 .1 - 4. 4) the text is examined considerinq exactly the same five points as are mentioned above.

9

3. Ketbod of research

3.1 General

In this experiment subjecte were given 6 scenarios, each containing a number of tasks. All these tasks were related to the receiver part of the cassette receiver and were presented in order of complexity; the simple scenario first, the more complex scenario at the end. In, for example, the first scenario the subjecte were asked to turn on the car radio and to tune to any particular station, adjust the volume, adjust the audio functions (Treble, Base etc.) on FM as well as on MW. In the scenarios subjecte had to;

1. tune to stations (using automatic tuning and manual tuning), 2. store a station on a preset button (using automatic tuning and manual

tuning), 3. let the receiver search for the five strengest stations (the so-called

Autostore function), listen to these stations and transfer them to the preset buttons on the normal FM or MW Band,

4. adjust the sound functions (Treble, Bass, Balance and Loudness).

The scenarios were presented to the subjecte in a written form, one scenario per page, every page containing all the tasks that constituted the scenario.

The subjecte were asked to 'think aloud' during the experiment. Their 'thoughts' were recorded on tape, tagether with the questions that were asked, the remarke that were made concerning the text etc. Now and then, the experimenter asked to continue to 'think aloud' if one of the subjecte was either se arching for, or reading information but stoppad to 'think aloud'.

For every subject the 'set up' of the receiver was identical: each subject started his or her scenario while the radio was switched off, while no stations were stored on the presets and autostore was not activated.

The cassette receiver was mounted in an adjustable frame, at knee level, under a table i.e., to simulate the actual positioning of a car radio in a vehicle •. The subjecte were seated bebind the table, on the left side of the cassette receiver.

Ouring the experiment, the experimenter measured the time subjecte were actually reading the instructions.

Every button that was operated by the subjecte during the experiment, was recorded by a remote computer (see section 3.3). Oue to technical probleme, however, the experiment only covered the receiver-part of the instructions. Recording of button oparation of the cassette-player was, up to the time of the experiment, not reliable enough.

3.2 Subjects

The six subjecte (three men, three women) ranged in age from 20 to 32 years. All subjecte had cooperated in various experiments (not related to car radios) at the Institute for Perception Research during the last year.

10

The subjects were paid for their contribution in this experiment, which lasted about one hour and twenty minutes.

3.3 Material

cassette receiver: In this experiment a Philips cassette receiver type oe 685 was used. The internal software of this modified cassette receiver has been chanqed in such a way, that after operatinq a specific button, a uniqua code is qenerated. Each code was send to a remote computer and stored as a separate event.

lleaote computer: The remote computer was developed in cooperation with the Institute for Perception Research and Philips Product Division Consumer Electronica. Three remote computers are installed in the cara of four subjecte, in order to obtain quantitative data about the usaqe pattarn of cassette receiver users over a certain time period. The remote computer stores the uniqua button codes that are qenerated by the internal software of the cassette receiver and also stores the time that has elapsed since the last button operation, with a resolution of l second. For the present experiment the remote computer was modified, to increase the resolution up to 5 milliseconde.

The stored codes were eend to and stored on the hard disk of a personal computer, at the end of each scenario. Subsequently, the personal computer was used to decode the stored button codes and to analyze the stored events. In order to record the utterances of the subjecte durinq the experiment without recordinq the noise cominq from the receiver, a small microphone, attached to a headset was used.

11

4. aesults

4.1 General

This chapter contains the results of the evaluation of the instructions of the DC 685 car radio. The results can be divided into two main data categorie& namely:

1. Insection 4.2.: The results of the protocol analysis. 2. Insection 4.3.: The registrations of the remote computer.

4.2 The results of the protocol analysis.

In order to make an analysis of the user protocols possible, the utterances of the subjecte, recorded during the experiment, were transcribed from tape to paper. This transcription served as a basis from which troublespots in the instructions are located.

Tables 4 .l - 4. 6 contain all the tasks that constituted each scenario, together with a list of knobs or functions that were necessary to complete the scenarios correctly. An exclamation mark (1) following "PRESET" indicates that a station is stored on one of the presets. An exclamation mark (!) following "AO'I'OSTORE" indicates that autostore is programmed. Consequently, the absence of an exclamation mark indicates either: listening to a station stored on a preset, or pushing the autostore button for less than 2 sec. in order to listen to one or more of the so called "autostore stations". The subsequent parts of an action sequence are linked with the ">" symbol. Optional choices are separated with the "/" symbol.

The six scenarios, that were presented to the subjecte in written form, contain a number of identical tasks (i.e. switch the radio on, adjust the volume level, adjust treble and bass etc.). This means that there is an overlap of a number of these tasks in the scenarios. Consequently, there is a number of tasks in each scenario that were new to the subjecte. There­fore, Tables 4.7 - 4.12 contain the new tasks of each scenario, in which the tasks that were already presented in one of the preceding scenarios, are omitted. Thus: the tasks that were already presented in scenario l (Table 4.1) are omitted in Table 4.8; the tasks that were already presen­ted in scenario 2 (Table 4.2), are omitted in Table 4.9 etc. Hence, Tables 4.7- 4.12 contain a summary of the actual tasks that were presented during the six scenarios.

12

Scenario 1.

l.Switch on the radio. ON

2.Listen to four (arbitrary) BAND>AUTOMATIC TUNING> VOLUME FM-stations.

3.chartge the volume level. "LARGE KNOB"

4.Change the Treble and Ba ss TREBLE/BASS>"LARGE KNOB" setting (according to your own preferenee) •

5.Listen to four (arbitrary) BAND>AUTOMATIC TUNING HW-stations.

6.Change the volume level. VOLUME

7.Change the Treble and Ba ss TREBLE/BASS>"LARGE KNOB" setting (aeeording to your own preference).

s.switch off the radio. OFF

Table 4.l:The left column eontains the tasks for scenario 1 that had to be performed. The right column contains the oorreeponding knobs or funetions that had to be used in order to complete this scenario correctly.

Scenario 2.

!.Switch on the radio. ON

2.Tune to 99.2 MHz on the FM. BAND>MANUAL TUNING

3.Change the volume level. VOLUME

4.TUne to 675 KHz on the MW. BAND>MANUAL TUNING

S.Quickly seareh for other stations wait for more than 50 seconds (as in the former scenario). then use AUTOMATIC TUNING/OFF>ON/

BAND/ PRESET / AUTOSTORE

6.Switeh off the radio. OFF

Table 4.2:The left column contains the tasks for scenario 2 that had to be performed. The right column contains the eorresponding knobs or functions that had to be used in order to complete this scenario eorrectly.

13

Scenario 3.

l.Switch on the radio. ON

2.Tune to an arbitrary BAND>AUTOMATIC TUNING FM-station

3.Change the volume level. VOLUME

4.Store this station on preset 1 PRESET 1 I

S.Tune to an arbitrary BAND>AUTOMATIC TUNING AM-station.

6.Change the volume level. VOLUME

7.Store this station on preset 1 PRESET 1 1

a.switch off the radio. OFF

Tabla 4.3:The left column contains the tasks for scenario 3 that had to be performed. The right column contains the corresponding knobs or functions that had to be used in order to complete this scenario correctly.

Scenario 4.

!.Switch on the radio. ON

2.Tune to 100.1 MBz on the FM Band BAND>MANUAL TUNING

3.Change the volume level. VOLUME

4.Store this station on preset 1 PRESET 1 1

S.Tune to 750 KHz on the AM Band BAND>MANUAL TUNING

6.Store this station on preset 1 PRESET 1 1

7.Switch off the radio. OFF

Table 4.4:The left column contains the tasks for scenario 4 that had to be performed. The right column contains the corresponding knobs or functions that had to be used in order to complete this scenario correctly.

14

-

scenario 5.

1.Switch on the radio. ON

2.Let the radio search for more BAND>AOTOSTORE I than ene station on the FM Band.

3.Change the volume level. VOLOME

4.Listen to the stations found. PRESETS 1 - 5

S.Let the radio search for more BAND>AOTOSTORE I than one station on the AM Band.

6.Listen to the stations found. PRESETS l - 5

7.Switch off the radio. OFF

Table 4.S:The left column contains the tasks for scenario 5 that had to be performed. The right column contains the eerreeponding knobs or functions that had to be used in order to complete this scenario correctly.

Scenario 6.

1.Switch on the radio. ON

2.Listen to the FM stations you BAND>AOTOSTORE just found (in the fermer scena-rio).

3.store these stations on the pre- PRESET 1>MANOAL TONING>PRE-sets. SET 11>AOTOSTORE>PRESET 2>

MANOAL TONING>PRESET 21 etc.

4.Listen to the AM-stations you BAND>AOTOSTORE just found (in the fermer scena- -rio).

s.store these stations on the pre- PRESET l>MANOAL TONING>PRE-sets. SET 11>AOTOSTORE>PRESET 2>

MANOAL TUNING> PRESET 2> etc.

6.Change the Treble and Bass TREBLE/BASS>"LARGE KNOB" setting.

7.Switch off the radio. OFF

Table 4.6:The left column contains the tasks for scenario 3 that had to be performed. The right column contains the eerrasponding knobs or functions that had to be used in order to complete this scenario correctly.

15

Scenario 1.

l.Switching the radio on.

2.Selection ot the wave range.

3.Using Automatic Tuning on I'M and AM.

4.Adjustment of the volume level.

S.Adjustment ot the sound­tunctions using the Treble and Bass selector together with the "large

6.Switching the radio otf.

ON

BAND

AUTOMATIC TUNING

VOLUME

TREBLE/BASS>"LARGE KNOB"

OFF

Tabla 4.7: New tasks that were presented in the first scenario.

Scenario 2.

l. Using Manual Tuning on FM and AM. MANUAL TUNING

2.Returning from Manual Tuning to Automatic Tuning.

wait for more than 50 sec./ AUTOMATIC TUNING/ OFF>ON/ BAND/ PRESET/ AUTOSTORE

Tabla 4.8: New tasks that ware presented in the second scenario.

sceuario 3.

l.Storing a station on preset 1. AUTOMATIC TUNING>PRESET l!

Tabla 4.9: New tasks that ware presented in the third scenario.

Scenario 4.

l.Storing a specific station on preset 1.

MANDAL TUNING>PRESET 11

Tabla 4.10: New tasks that were presented in the fourth scenario.

16

Scenario s.

l.Programming with Autostore on FM and AM.

2.Using Autostore on FM and AM while the radio is in the autostore operation mode.

BAND>AUTOSTORE I

BAND>AUTOSTORE>PRESETS 1 - 5

Table 4.11: New tasks that were presented in the fifth scenario.

Scenario 6.

!.Entering the Autostore operation mode and listen to the earlier (earlier programmed) Autostore stations.

2.Transferring the Autostore sta­tions to the normal FM and AM band.

BAND>AUTOSTORE>PRESETS 1 - 5

PRESET 1>MANUAL TUNING>PRE­SET ll>AUTOSTORE>PRESET 2> PRESET 2>MANUAL TUNING>PRE­SET 21>etc.

Table 4.12: New tasks that were presented in the sixth scenario.

4.2.1 The information that was searched for.

It is possible to il1ustrate the amount of effort it took for the subjecte to cope with the instructions. However, an exact representation of, for example, the amount of information that was read by the subjecte, the number of subjecte that read identical parts of the text etc. would become too -complex and thus incomprehensible. Most of all, such an illustration 1acks the power of generalization, since it would only be applicable to the 6 subjecte that participated in the present experiment. Due to these representation difficu1ties with regard to the information that was read, and the methodological shortcomings, representation is restricted to that of Tables 4.13 - 4.17. In Tables 4.13 - 4.17 all the information that was read out aloud by the subjecte, during their performance of the tasks, is marked. Some of the information was read by more than one subject i.e., the subsections "Hoge en lage tonen", "Programmeren met Autostore" etc. Besides, some of the subjects read the same parts of information more than once.

17

11 • ~ depiets the lines from which

information was read.

The underlined text indicates what information was read.

Nederlands

-------·-------~--- f

GEBAUII<SAANWIJZING ®Toetsen voor automatisch zenderzoeken en handafstemming

Sla tijdens het lezen van de gebrulksaan· ~ - = frequentie omhoog wijzing ook pagina 3 uit. * - == frequentie omlaag

OVERZICHT VAN BEDIENINGSORGANEN Ook gebruikt voor intoetsen van de bevei­ligingscode

------ f.@ Voorkeuze/programmeertoetsen (1 • 5) ~ GELUIDSREGELING . @ INFO-toets voor verkeersinformatie

......... - · ----·- ·-------·· ------------ @ OK-toets voor verkeersberlchten-identifi-calie

rfif~mf=l~~~;;:9~~3n·~@ AUTO STORE op MG en FM ~ @ Golfgebiedschakelaar !BAND)

~ CD Aan/uil-schakelaar (ON) ® Keuzetoets voor voor/achter-regeling

(FAO) 4 ® Keuzetoets voor balansregeling fBAU

@ Keuzetoets voor lage tonenregeling (BASS -LO)

® Keuzetoets voor hoge lonenregeling (TREBLE - Hl)

® Volumeregelaar, ook regelaar van fader, balans, hoge en lage tonen (LEVEL-VOL}

® Loudness-toets (LOUO) ·

@ Keuzetoets voor radio of cassettespeler (MODE)

·-· ---···-------CASSETIESPELEA

0 0~ 00

0 @Toets voor Music Sensor System (MSS)

om het vorige of het lopende stuk muziek te herhalen als toets (( wordt ingedrukt, of om het volgende stuk muziek af te spelen als toets )) wordt Ingedrukt

® Aan/uit schakelaar voor Dolby® B NA systeem {00)

@ Keuzeschakelaar voor 'Metai/Chromium'-0 0 en 'Ferro'-cassettes (ME/CA)

O O ICO~~~ij~~~~~~ @) Cassetie-opening

0 IC @)Toets voor omkeren afspeelrichting (( J) en

LL~· ::=:::J~~~~~!l~~~~~tJ uilwerpen van de casselle c .,t.@ en@ Toetsen voor snelspoelen («en »I De richring van het snel vooruit- en terugspoelen hangt al van de momentele alspeelrichting zoals het display aangeeft. ® Digitale schaal (display}

Beschadig het display niet door erop te drukken of te wrijven

·•• Ruisonderdrukkingssysteem gefabriceerd onder 0-centie van Dolby Laboratorles Licensing Corporstion. Het woord 'Dolby· en het symbool van de dubbele D zijn handelsmerken van Dolby Labors/ories Licensing Corporation.

GELUIDSWEERGAVE

4 AlGEMEEN

In deze autoradio worden de instellingen van het volume. de balans, de fader (voor/achter-regeling), de hoge en de lage tonen langs elektronische weg geregeld. ·

E!!se insteRing Q!l}eurt In staPPen met de grote knop Normaal lunetjoneen deze aiS volumerege­laar. ÖÏÜkt u echter oo éên van de loetsen BALANCE. FAQEB IBEBLE of BASS dan verander! de functie ·~an de gro!e knoo in respectlevellik balans-. fader­of hoge- dan wel lage-tonenregelaar. Op hel display verschijnen dan de lelters B A l, F A 0, H I (high= hoog) of l 0 (Jow =laag). Met de grote knop stel! u nu de gekozen functie op hel gewenste niveau In. Dil niveau wordt automatisch in het geheugen opgenomen. Korte lijd (10 seconden) na de laatste instelling herkrijgt de grote knop vanzelf weer de functie van volumeregelaar. Als u echter binnen deze tijd op nogmaals dezelfde keuzetoets (b.v. BALANCE) drukt, dan wordt de grote knop onmiddellijk weer volumeregelaar.

g h k

Op hel display kunnen verschijnen: •· functle-indicalie LOOD voor loudness b.1 veldslerkle-indicalle OI) FM, LG en MG (lol op

4 segmenlen die naar links wijzen) b.21ndicalie voor de alspeelrichting tijdens het afspelen

(4 segmenten die naar links of naar reehls wijzen) b.31ndicatie tijdens hel snelspoelen en tijdens MSS

(l'lllker en rechter knipperende pijlen) c. lunetie-Indicatie ME/CR voor melal- of chromium

cassettes (a"éèn Ujdens hel afspelen van een cassette}

d. lunclie-lndicalie {]() voor OOLBY NR ingeschakeld (aUèen tijdeiJS het afspelen van een cassette}

e. zenderlrequentle, of de lelters CAS (tijdens het afspeten van een cassette}. of de letter ·- C- ·tijdens de wachttijd nadat een niet correcte beveiligings­code is ingevoerd

"J(f. la91s1 bediende vqork:Ji;lzeloels 1 1 tol 5). tevens een In leetie (segmenten e na elkaar oplichten) gedu-Opmerking: Het Is aan te bevelen om de grote

knop tijdens het autoriJden alléén als volumere· gelaar te gebruiken.

· ~ AAN/UIT • VQlUME

rende de wachttijd, die volg! na hel invoeren van een verkeerde beveiligingscode

g. Indicatie AST voor AUTOSTORE h. gollgebleden: l W ( = LG), MW ( = MG). FM 1 ol FM2 L de signaalindicatie STEREO (alléén op FM) J. functie-Indicaties INFO en DK k. signaalindicatie SK

• Zet de radio aan met toets ON. ~ INSTELLEN VAN DE GELU!DSFUNÇT!ES

• Regel het volume met de grote knop. Tof!'llchtlng:Na het aanzetten hoort u hel geluld met dezelfde Instellingen als op het moment dat u de radio ultsc:hakelde. Was evenwel het volume op een te ec:hter hoog niveau Ingesteld dan zal. om redenen van veiligheid, het geluld op een lager niveau terugkomen dan toen · u het apparaat uitschakelde,

54

Balans

• Druk op de balanstoets (BALANCE). De lrequenlie OI) hel display wordl vervangen door de Ieliers B A l. Als u de grole knop verdraait verschijn! de Instelling van dj! slereobalans. uitgedrukt in cijfers.

• Draai aan de grote knop en regel de balans *LOUDNESS tussen het linker en rechter kanaal. · Wordt de grole knop niet binnen 10 seconden bediend dan wordl zijn lunclle vanzelf weer volumeregelaar. Hel display loool weer de algestemde frequentie.

Linker ksnssl: Draalt u de grote knop vanuil de middenstand linksom, dan loont hel display eersl - 0 ·, daarna 1 • -, 2 - • enz lol maximaal 9 - •.

Rechter ksnssl: Draall u rechtsom dan ziel u • - 1, - • 2, enz. tol maximaal • - 9.

Fader (voor/achter-regeling)

• Druk op de fader-toets (FADER) en regel de geluidsverdeling tussen de luidsprekers voorin en achterin met de grote knop. Hel display loont daarbil de Ieliers F A 0. Als u de grote knop draait toont hel display de instelling uitgedrukl in cijfers (9-- via • 0- naar -- 9).

Hoge en lagetonen

.:Jtl. • Stel op qeliike wijze de hoge tonen 4 (TREBLE l en lage tonen (BASSl in goor op de ~ desbetreffende keuzetoets te drukken.

.~

Het display toont respectlevelijk H I or l 0. Opmerl<fng: Bij hel instellen van hoge en lage lonen loont hel display een ma!limale waarde van 4 namelijk: 4 - -. 3- ., 2 - •• 1 • -.- 0 -•• - 1, •• 2, - - 3, • - 4.

00 00

0 • Druk, Indien gewenst. op de toets LOUD. Hel display loonllOUO.

• Druk nogmaals op toets LOUO als u de loudness functie wilt uitschakelen. Als de loudness-functie Is ingeschakeldworden de hoge en lage lonen meer versterkt Hel effect van de loudness is afhankelijk van de instelling van de toonregelaars.

55

RAOIO·ONTV ANGST I ·-·- ·~---------··-

Als na enige tijd (meer dan 60 seconden) weer een van de alstemtoetsen wordt bediend, begint hel automatisch afstemsysteem opnieuw naar sterke zenders te zoeken.

·----------------• • alo een GOLFGEBIED - BAND ~ ~f:kal.~~.lll: ------------------ displayookhetnummervan

00 zeloets. Opme'*lng: Hel automaUsch alstemmen kunt u met behulp van een schakelaar ook op alstand bedienen, echter alleen in de opwaartee richting. (Zie INBOUWVOORSCHRIFT).

1/- AUTOMATISCH PROGRAMMEREN • Kies hel gewenste golfgebied door één- (AUTO STORE) maal of vaker op de BAND-keuzetoets te _____ ....;_ _________ _ drukken. ~ AUTO STORE wer!st zowel op de FM-band als 2P de

..,.. MG-band. Hel Is een uilgebreid zenderzoeksysteem, Het display toont het gekozen golfgebled: waarmee u met èèn druk op de AUTO STORE-toets yjj[ LW voor langegolf. 11r extra zenderS OD FM en MG au!gma!jsçh kyo! se!ec-MW voor middengolf, .". llwm. en direct onder de voorkeuzetoetsen program-FM 1 voor FM ol meren. FM2 voor FM. -oF AUTO STORE Is uilecma!e nullig als u zich in een gebjed Opme'*lng: Om de voorkeuzemogelijkheden. te .>A • I vergroten is de FM-band dubbel uitgevoerd In FM 1 en ..,.. i FM2. -" Elke band bestrijkt hel gehele FM-gebied (67,5 MHz tol "' 108 MHz). Dus kunnen in totaal 10 in plaats van 5 -fllreguenlles te kennen. =M-stallons worden geprogrammeerd.

AUTOMATISCH AFSTEMMEN omhoog - of omlaag

00 00

-'lt Programmeren met AUTO STORE

00 00

0 0 ." s.Kies eerst de FM-band of de MG- mfAI ge

l.L~:::::J::~~~~~~~~~~:;jJ""' BAND-keuzetoets. ~ b. Druk langer dan 2 seconden op de AUTO

• Druk even op één van de afstemtoetsen ,v.. STORE-toets om in de AUTO STORE­omhoog (-) of omlaag (-) en u ontvangt na .""_ programmeersta~d te komen van het korte tijd een station. ~ gekozen gollaebted. U hoort een twee-• Druk nogmaals op dezelfde toets en u fl-' tonige ~leg ï.f . . . . ontvangt even later het volgende station in de it - In het dtsplay kmppe~t. de tndtca~te AS~ en richting van de zoekafstemming. de freg!Jenlle-aandutdtng verdwunt eryn.

- De frequenties op het display veranderen in stappen '* Als d van 50 kHzvoor FM en9 kHz voor MG en 1 kHz voor LG . .tf­- Als de hoogsle freQUentie is bereikt (b.v. voor FM: 108 MHz) gaat hel afstemmen verder vanaf de laagste frequentie (voor FM: 87,5 MHz) en omgekeerd. - Hel automatisch zoeken naar zenders rt In alle I n o rad'10 naar sterke ze

schikle zenders o een

56

op voorkeuzeloet~ 1 met AUTOSTORE Is geprogram- + nder meerd. .,. Hebt u de LG-band gekozen, dan hoort u een-if louttoon. ~ over ezel • Druk nu éèn maal (voor MG)ol twee maal (voor FM) op - • es een de BAND-toets. )1.,

JA

"' • Kies de andere band (MG of FM) met de "'f maar de

.,.... BAND-keuzetoets. """ .:1- • Druk opnieuw op de AUTO STORE-toets !

totdat de AST -indicatie gaat knipperen. en F ban en de zen er wor

Nu worden vijl stalloos van hel andere golfgebled geprogrammeerd.

voorkeuzetoets geprogrammeerd.

een tweetonige piep .

00 00

0 - Als een zender met verkeersjnformatlg Is gevoolfcg 'J Opmerking: wordt de INFO-stand automatisch meegeprogram- '* uikt m meerd. ~

1Ziëlii:loldsluk: VERKEERSINFORMA TIE). .,.,....,.,.,.....,..,=

-en-

Bedienen van AUTO STORE oM • Druk kort op belde afstemtoetsen ... en -.i( tegelijkertijd. Oe functie van de toetsen ..fl verandert van 'automatische afstemming' in

nci()r=~~~~s;;;;9fi=9=i:::=n 4 'handafstemming'.

Na het programmeren behoeft u slechts: ..,c Snel hsndsfstemmen s.De FM- of de MG-band te kiezen mei ~ • Houd één van de afstemtoeisen .... of-

BANO-keuzetoets. -111( ingedrukt. b KorlopAUTOSTORE-toetstedrukken·het ..:t~"Na 1 seconde wordt de lre uenlieband snel a

• . ' ~ a u oe s saa. e ra 10 IS 1 ens ze display toont de indicatie AST. handeling sli.

c.Op één van de voorkeuzetoetsen (b.v. -Na de hoogste frequentie volgt de laagste frequentie en omgekeerd.

toets 4) te drukken; U ziet op het display de -'11 oe alstemtoetsen krijgen weer hun functie 'automatisch frequentie en het nummervan de ingedruk- iCZ te u:

te voorkeuzetoets. ~ ~: ~~~LOJ:J~~~dllltlun.dwkl. U kunt de AUTO STORE-bedieningsstand ""3. or BAN - z v n voorkeuze-

opheffen door op de BAND-toets te drukken. "'*' · · Opmerking: Als u de handalslemming kiest wordt de

Opmerkingen INFO-stand uitgeschakeld.

- 1

57

VOORKEUZETOETSEN {1 • 5)

Programmeren van de voorkeuzetoetsen

~ s. Kies het gewenste golfgebied (LG, MG, FM1 of FM2) met de BAND-keuzetoets.

~ b.Stem nauwkeurig af op een gewenste .- zender met behulp van:

SEARCH (Automatische afstemming) of HANDAFSTEM MING.

Ir c. Programmeer de gevonden zender als volgt: Druk zó lang op de gewenste voorkeuze­toets (b.v. toets 1) tot u een tweetomge piep JJ hoort als teken dat de zender­frequentie in het geheugen is opgenomen. Op het display verschijnen: Het golfgebied. de frequentie en het toetsnummer waaronder u de zender hebt geprogrammeerd. Opmerkhrg: Als u korter dan 2 seeonde op de voorkeuzetoets drukt wordt de frequentie opgeroe­pen die de vorige keer was geprogrammeerd.

:1- • Programmeer op dezelfde wijze de volgen-~ de voorkeuzetoets.

• Herhaal bovengenoemde handelingen voor de overige golfgebieden.

Opmerking: De INFO-stand kan tegelijk worden meegeprogrammeerd. Zie hoofdstuk: VERKEERS­INFORMA TIE • INFO-stand meeprogrammeren.

. 58

Bedlening van de voorkeuzetoetsen

Nadat de radio Is geprogrammeerd behoeft u slechts: s. Op de BAND-toets te drukken om het

gewenste golfgebled in te stellen. b.Op één van de voorkeuzetoetsen (b.v.

toets 4) te drukken .

Opmerking U kunt een zender van de ene voorkeuzetoets op een andere programmeren fb.v. van toets 1 op toets 3) met behulp van 'handafstemming' en wel als volgt 1. Kies de gewenste zender door op één van de

voorkeuzetoetsen (b.v. toets 1) te drukken. 2. Druk kort op belde alstemtoetsen (-en -llegelljker­

lijd voor hel InslaHen van de handafstemming. De voorkeuze-indiealle verdWijnt uil hel display.

3. Druk zó lang op de gewenste voorkeuzetoets fb.v. toets 3) totdal u een tweetonige piep P hoort. Deze zender Is nu o~ deze toets geprogrammeerd.

De tussenstap met de stand 'Handafstemmlng' is nodig om ongewenst programmeren Ie voorkomen wanneer u per ongeluk te tang op èèn van de voorkeuzetoetsen zou drukken.

MONO/STEREO ONTVANGST

Oe radio komt op FM-band altijd in de stereostand. Hel display loont hel woord STEREO als een stereozender wordt ontvangen. Bij afnemend signaal gaal uw ontvanger autornallsch en geleidelijk over op mono­weergave. Hel woord STEREO verdWijnt uil hel display.

00 00

0 Als het signaal weer sterker wordt schakelt de radio weer over naar stereo.

SIGNAALMETER

~

p J

LOUD ...:.-. ............ ME/Cfüi, . I-J . . ~ jllll(j .. • - IXÎ. ·U

L• ~i • •L• o•..L· ~~. •...... ~.,,;···.·.t .. _:·i··. I IF ••·• ...... s· ..... -FM·.· - •!,Wil, ftif ,<!\ST; stEREO,,: INFO •.. Sl(f'*~f

De kwaliteit van hel ontvangen radiosignaal op LW, MW en FM wordt aangeduid door de linker pip boven lrl het display: - Geen segmenten: zwak signaal, - twee segmenten: bruikbaar signaal, - vier segmenten: sterk signaal. Als de veldsterktemeter geen segmenten toont, Is het raadzaam op een andere zender alle afstemmen.

VE~~EEAS~FO~MA_~IE -~!!_~-~p FM

Verkehrsfunk

Geldt alléén voor landen die het INFO-systeem toepas­sen (West-Oilitsland, Zwitsertand en Oostenrijk}.

B•l•ntrl.lk:Gebrulk de INFO-toets en de OK-toets niet In diè landen waar geen verkeersinformatie volgens hel INFO-systeem wordt uitgezonden. Doel u dat wél. dan ontvangt u geen FM-signaal.

-Deze autoradio-cassellespeler Is uilgerust met een SKIOK-decoder ISK = Senderkennung = Zenderher­kenning. OK= Ourchsagekennung == Berlchtherken­nlng) voor verkeersinformatie. Deze decoder ldenlill­ceert INFO-zenders op de FM-band die een piloot· frequentie (SK-slgnaal) uitzenden en herkent verkeers· berichten die door zo·n zender worden uitgezonden (OK -signaal).

Zenderherkenning-INFO

00 00

0 INFO: Druk op de INFO-toets. De radio staat nu In de INFO-stand. - Hel display toont de indicatie INFO. De signaalindicatie SK is aneen zichtbaar als de radio staat afgestemd op een zender die verkeersinlormalie uitzendt (z.g. INFO· zender). - Indien de radio niet Is afgestemd op een INFO-zender, dan hoort u een piep (waarschuwingstoon). De radio gaat naar de eerstvolgende INFO-zender zoeken (AUTO INFO SEARCH). In deze positie stemt de radio uitsluitend af op INFO-zenders.

Berichtherkenning - OK

00

DK: Bij radio-ontvangst: Druk op de DK -toets als u alleen maar verkeersinformatie wilt ontvangen. - De INFQ..stand wordt Ingeschakeld en de radio valt stil. Het display loont de (functie-) indicaties INFO en OK. Zodra er verkeersinlormaHe wordt uitgezonden, scha­kelt uw autoradio automatisch over op het door uzelf vooralingestelde geluidsniveau. Na het bericht valt de radio weer slil.

59

4.2.2 Correct and incorrect actions performed by the subjects

The results of the tasks that are performed can be divided into two cate­gorie&. These tasks were either solved, more or leas, successful or were solved unsuccessful. Here, unsuccessful is defined as trying to solve a taak by using an inappropriate function for more than three times. Fur­thermore, the successfully and unsuccessfully solved tasks can be further divided into two categorie& namely: 1. Tasks wherefore information from the manual was read. 2. Tasks wherefore no information from the manual was read.

All mentioned categorie& combine to a 2 x 2 matrix. Table 4.18 illustrates for all subjecte the, successfully or unsuccessfully solved (parts of) tasks. The two upper columns on the right part of this table contain the number of subjecte that either read the information with regard to the successfully solved tasks stated in the middle column, or solved the task without reading any of the information concerned, i.e., by trial and error. The lower right columns contain information regarding incorrectly solved tasks for which either intermation was read or not read.

Table 4.18:

CORR/INC P'UNCTION REAO NOT REAO

ON/OFF 2 4 c BAND 2 4 0 AUTOMATIC TUNING 4 2 R VOLOME 1 5 R BAL,HI,LO 2 1 E MANUAL TUNING 4 1 c PRESET 1 5 0 T AUTOSTORE ! 3 0

AUTOSTORE 2 0 AUTOSTORE>PRESETS 2 2

REAO NOT REAO

I ON/OFF 0 -N BAND 0 -c AUTOMATIC TUNING 0 -0 VOLOME 0 -R BAL,HI,LO 3 -R MANOAL TUNING 1 -E PRESET I 1 -c AUTOSTORE I 3 -T AUTOSTORE 4 -T AOTOSTORE>PRESETS 2 -

The upper secend column contains correctly performed tasks. The upper third column contains the number of subjecte that read the concerning information. The upper fourth column contains the number of subjecte that did net read the concerning information but did succeed in successfully performing the tasks. The lower secend column contains incorrectly performed tasks. The lower third column contains the number of subjecte that read the concerning information but performed the tasks incorrectly.

22

The "incorrect/nothing read" column is not filled, since all incorrectly solved actions for which no information was read might have been performed for multiple reasons •. For instance, subjecte might have tried out some of the functions to verify an assumption, or to satisfy their curiosity regarding that function etc. This implicates that the observations in the "incorrectfnothing read" column would be confounded and would only lead to speculative conclusions. Moreover, this experiment focusses mainly on locating the possible trouble spots in the instructions and it is therefore only interesting to concentrata on data that can help locate these troublespots.

4.2.3 Assumptions of the subjects regarding the working principles of the car radio.

The design of the experiment made it possible to record, and make interen­ces about, correct or incorrect assumptions that were held by the subjecte, concerning some of the working principle& of the car radio. As stated in section 2. 6 it is useful to determine what the customer or user assumes about the product. Likewise, it is also important to define what incorrect assumptions the customer holde. Sometimes subjecte explicitly spoke out an assumption while coping with the instructions. Other assumptions became clear by means of explicit questions, asked by the experimenter during the experiment, for instance, when a subject deviated from an expected action sequence, or persevered on an, incorrect, action sequence. Table 4.19 contains correct as well as incorrect assumptions that were either spoken out spontaneously by the subjecte or became clear after explicitly asking the subject. The left column contains a description of the assumption. The middle column indicates whether the assumption is correct or incorrect. The right column contains the number of subjecte that held the assumption concerned.

4.3 The registrations made by the remote computer

4.3.1 Performance of the subjects

The remote computer facilitated recordinga of all action sequences of the subjecte during the experiment. consequently, it was possible to compare the actions of the subjects with the actions that had to be undertaken, as two data sets.

An analysis of both sets of data made it possible to objectify the actual actions and expected actions and depiet them as so called "Progression Graphs" ( Figures 4 .1 - 4. 6) • In these Progression Graphs, a horizontal sequence of rectangular figures, beginning with "ON" and ending with "OFF", depiets the expected or correct action sequence for each scenario. Every rectangle in the horizontal direction represents a function or knob that had to be used. Every deviation of the expected action sequence that was made by the subjecte is depicted in (upward) vertical direction. A vertical, upward, line between two reetangles indicates that the deviation is started befere thë next depicted action or action sequence. A vertical, upward, line starting on top of one of the reetangles indicates that the incorrect action is alternated with the correct action or part of a correct action sequence from which the upward line originates. Whenever two or more subjecte performed the same incorrect action, it is depicted by multi layer

23

rectangles, with the corresponding number of subjecte as a numerical value on top of them. The incorrect actions that were performed by only one of the subjecte are depicted as single layer rectangles. Figure 4.7 contains the legend for Figures 4.1 - 4.6.

All scenario& except the sixth one were, more or lees, successfully comple­ted by the subjects. Due to the large number of errors during the aixth scenario, only the firet part {FM part) of this scenario is depicted. The subjecte showed very differing actions during the second (AM) part of this scenario, merely to try out every conceivable action. None of the subjecte aucceeded to perform the sixth scenario successfully without help of the experimenter.

24

2

~--------~ A~. TUNING VOL

Fig. 4.1: Progression Graph Scenario 1

6

I Acfusllng Treble and Bass I L ___ on}!' ___ _ I

BAND AUTOI.I. TUNING

I Ad}usling Tmble and Bass I L---~~--_1

4

MODE

STORE/ 1---1 STORE/ 2

~-----------1 PRESETS PRESETS

6

I : lnltlallng Manusl Tuning I '----~~.:.... ____ ,

Fig. 4.2: Progression Graph Scenario 2

Fig. 4.3: Progression Graph: Scenario 3

Programming proset I on FM uslng Autom. Tuning

(

I I Programming presar I M FM uslng Manual I I wrn~ t

'------~--------------__J

I I : Progtammfng presar t MAM uslng Manual I '-- _____ ..!.urn"!J_ _____ I

Fig. 4.4 Progression Graph Scenario 4

,......_ _ ____.

I I lnlrlaUng Aulostoffl and lislening to lhe live I I strongest stations (FM) I L-~--------------~

Fig. 4.5: Progression Graph: Scenario 5.

I I

1

1

/nltlatlrw Autostom and llstsnlng to lh9 flve 1

1 slrongtlst staNons (AM) L ___________ l

ETC.

BAND

I I

ETC. I I .___ _ __.I

: Ustenlng fD fte aurostorfl I I TransfBf' of stations programmsd by autostore to lhe notmal FM preset locallons I L ____________________________________ J ___ _2ta~----1

F~g. 4.6 Preigression Graph: Scenario 6. Due to the complexity of thls scenario and lhe larger number of errors that were mad9 in lhe second (AM) part, only lhe first part of the scenario Is presented.

EJ !BAND I lsTORE/1

lsroRE J

MANUAL TUNING TUNING - UP-DOWN

AUTOM. TUNING

IPRESETS I IPRESETS/1

J:~~:?r.H VOL I r~UD/0

UNCT

I I AUDIO FUNCT

Horizontal direction depiets ths path that had to bs foliowed by ths subjscts.

Vsrtical dwiations dspict ths errors, made by ths subjscts.

Error (function)8b was made prscssding ths (sxpsctsd) tunetion 8.

Error (funaion)Bb was made allemaling ths (sxpsctisd) tunetion 8.

Ths numbsr of subjects, that made an error, is dspictsd by ths numbsr of /ayers and a numerical va/ue.

"Text• dep/cts the function, lnitiated by the subject.

Selsction of the wavelength ••

Using Autostore lor sslecting and programming ths five strongest stations.

Operation of Autostore •

Manua/ tuning: step by step or last.

Ssa.rching fora station using automatic tuning.

Using one or more prestilt buttons

Programming (IJ ons or mors preset buttons

Adjustment of the audio functions Treble, Bass,or Ba/ance

Attempt to adjust Trsble, Bass or 8alance without using the •Large knob•

Fig. 4.7: Legend tor ths Progersss/on Graphs 1-6.

Uttered assumptions

1. 'l'he Automatic 'l'uning knob can be used to listen to stored stations

2. 'l'uning can be done using presets instead of Automatic or Manual 'l'uning

3. FM1 differs from FM2.

4. 'l'he stations that are found with Automatic tuning are stations that were already stored in the radio by someone.

5. The car radio always contains a number of preselected stations. (In other words: it is not necessary to store stations yourself).

6. Manual 'l'uning can only be used by repeatedly pushing the SEARCB button (in stead of pushing the SEARCH button constantly).

1. 'l'he Automatic Tuning knob can be used to tune to stations that are not stored.

8. Storing an FM station on preset 1 deletea the AM station on preset 1

9. 'l'he presets can "contain" only 5 stations.

10. The radio can "follow" a station over a long traveling distance.

11. once the AST button is pusbed for more than 2 seconde, the stations that are found are stored on the presets will replace the stations that were stored earlier by the user.

12. 'l'he AST stations remain on the presets even after selecting another wave range.

13. Switching to another wave range deletee the aarlier found autostore stations.

14. 'l'he car radio will keep the found autostore stations, even if the radio has been switched off.

incorrect

incorrect

incorrect

incorrect

incorrect

incorrect

correct

incorrect

incorrect

incorrect

incorrect

incorrect

incorrect

correct

Number of Subjecte

1

1

2

1

1

2

2

1

2

1

2

2

2

1

'l'able 4.19: Number of subjecte (right column) aharing the uttered assumptions (left column) concerned. 'l'he middle column indicates if the assumption is correct or incorrect.

32

4.3.2 Deduced incorrect assumptions.

It also became evident that certain incorrect assumptions that were held by the subjecte could be deduced from one or more actions undertaken by them (i.e. an attempt to switch on the radio by using the volume knob). Table 4.20 contains the deduced incorrect assumptions. The right column contains the number of subjecte aharing the incorrect assumptions concerned.

Deduced incorrect assumptions

The radio can be switched on using the volume knob.

Adjustment of the sound functions can be done by operating one button (either Treble, Bass or Balance).

After adjusting Treble, Balance or Bass: it is not necessary to push the used button again, in order to "switch off" the function used.

Tuning to any particular frequency can be done using Automatic Tuning (whereas Manual Tuning should be used).

Manual Tuning can (only) be used by pushing the SEARCH button repeatedly.

After pushing the SEARCH button, another function can be operated immediately (whereas the radio is still busy to find a new station).

While the Autostore function is searching the five strengest stations, these stations can be listened to already during the search process.

Number of subjecte

1

6

2

6

3

1

3

Table 4.20: Number of subjecte aharing the deduced incorrect assumptions in the left column.

4.3.3 Errors that were made by the subjects

Table 4.21 contains a summary of the errors (also depicted in the progression graphs) that were made in the first part of each scenario (the FM part). The left column contains the expected actions, or action sequences, and the middle column contains the actions, or action sequences that were performed by the subjecte. The right column depiets the number of subjects performing the actions concerned. Here, only the errors made in the FM part are depicted since the first part of the scenario& contained tasks that were new to the subjecte which lead them to read the instructions. It is not unimaginable that errors in the AM part of the scenario& stem from other causes than obscurities in the instructions, i.e., curiosity, verification of assumptions, attempts to reach the ultimate goal by using shortcuts, etc.

33

Expected action

ON

BAND BAND

AUTOMATIC TUNING AUTOMATIC TUNING SOUNDF>LARGE KNOB

MAN.TUN>UP/DOWN MAN. TUN>UP /DOWN MAN.TUN>UP/DOWN MAN. TUN>UP /DOWN

Perfor.med action

VOL

PRESETS AUTOSTORE

EJECT MODE SOUNDF>SOUNDF>etc. (repeatedly using the Bass, Treble or Balance button)

AUTOZ.m.TIC TUNING AUTOSTORE I MODE PRESETS

Number of

1

1 1

2 1 6

6 2 1 1

subjecte

Table 4.21: Summary of the errors that were made during the first (FM) part of each scenario.

4. 3. 4 Amount of time needed for completing the scenarios and reading the instructions

Since the remote computer also facilitated time measurement, Table 4.22 contains, for each scenario, the time needed to complete each scenario. It should be noted, however, that such time measures are only a rough estimate of the effort, needed to perform the scenarios. The subjecte were not asked to complete the scenarios as quickly as possible. As stated in .section 4.2.2, the subjects differed concerning the amount of time spent at reading the instructions. Individual differences, concerning the total time spent to complete the scenarios, might account for an over-, or underestimation regarding the ease of applying the relevant information, when using the mean as a statistic. Since individual differences concerning the amount of time spent to read and locate information may account for similar distortions, the median is used as statistic. This way, the exact midway between the time scores is known. Table 4.22 contains the mediane regarding the total time spent for each scenario and the mediane concerning the amount of ~ime that was spent during each scenario at reading the instructions.

Scenario

1 2 3 4 5 6

Table 4.22:

Median ( Tasks) Median (Instructions)

619.0 seconde 387 seconde 714.5 , , 347 , , 188.5 , , 70 , , 118.5 , , 22 , , 599.5 , , 314 , ,

1301.0 , , 560 I I

Mediane, regarding the amount of time spent to complete each scenario (Tasks) and the amount of time spent at reading the instructions (Instructions).

34

5. Discussion and conclusions

5.1 General

The discuesion of the results and the conclusions that can be drawn from them are closely entangled. Therefore, this chapter contains the results of the protocol analysis, the remote computer registrations as well as the results of the walk-through check. Separating the discuesion and con­clusions would only slow the reader down, since he would have to jump from one chapter to another in order to get a full overview of the matter. By combining the discuesion with the conclusions into this chapter, a chronoloqical walk-through and discuesion of the existing instructions is made possible.

For reasons of convenience, photo copies of the instructions are printed on the left pages of chapter 5.3.1 - 5.3.10. This way, the subsequent sections in which trouble spots are 1ocated can be viewed instantly.

5.2 The overall structure of the instructions

It is assumed that the subsequent sections and subsections in the existing instructions of the DC 685 cassette receiver are indicated by means of:

a) the narnes given to the sections (e.g. "Automatisch afstemmen", "Voorkeuzetoetsen"),

b) color coding: headings printed in blue depiet chapters, headings printed in black depiet sections, etc.

Based on this taxonomy, the structure of the instructions is depicted as Figure 5.1. The current structure (see also Figure 5.3) includes four main chapters, namely: "Gebruiksaanwijzing", "Geluidsweergave","Loudness" and "Radio ontvangst". These chapters contain a number of sections which, on their turn, are further divided into a number of subsections. For a number of reasons, which are listed in section 5.3, another structure is suggested in Figures 5.2 and 5.4.

5.3 Alteratiens

The first (minor) alteratien is related to the section "Loudness". In the existing structure, the section "Loudness" is printed as a separate section. However, it is suggested here to include it as a subsectien of the section "Geluidsweergave" since it contains information related to the sound functions.

The main alterations, regarding the existing structure of the instructions, are related to the chapter "Radio ontvangst". This chapter should be divided into three (new) sections namely:

1) "Afstemming", in which information is included regarding the primary functions for tuning,

2) "Programmeren", in which information is included regarding the functions that require programming,

3) "Mono/Stereo ontvangst", in which information is included reqarding mono and stereo reception.

35

FIG. 5.1: Current structure of the DC685 Car radio.

Snel hand· afslemmsn

Instruci/ons DC 685 Cassette receiver

Program· meren aurostoro

G91ulds­mgellng

Radio Cassslfs­spelsr

Algemt~t~n AaWIIII· volume

FIG. 5.2: Suggested structure of the

DC685 Car,radio

Insis/ten v/d gsluldsluncllss

Instruci/ons DC 685 Gasselte receiver

ontvangst

BBdlrmsn van Stap voor aulosrors slap hand·

alstsmmen

Snslhand­alstemmen

Program­memn

Bsdlllnlng

The proposed structure above divides information which is new to the •novice reader", into functionally dissimilar categories. The eection "Afstemming" then will only contain information with regard to the primary functions of a car radio namely: tuning to stations. The section "Programmeren" then will contain all information with regard to those functions in which programming is an essential part of the functions. An effect of this restructuring is that it helps the reader to differentlate between the two primary functions of the car radio and, as a result, helps the reader to find the appropriate information in the text.

Another effect of this restructuring is that it can be applied to instructions of other Philips car radios in which, for instance, Autostore is not available. In these instructions the section "Programmeren" can be left out. The section "Afstemming", however, can be included as an already existing text module. With regard to the chapter "Radio-Ontvangst" (page 56) the order in which the subsequerit sections are presented now is as follows (see also Fig.S.l):

Chapter containing the sections

~-----1. "Golfgebied - Band" p. 56

~-----2. "Automatisch afstemmen" p. 56

~-----3. "Automatisch programmeren" p. 56 Radio ontvangst--------------~

~-----4. "Handafstemming" p. 57

~-----5. "Voorkeuzetoetsen" p. 58

~-----6. "Mono/Stereo ontvangst" p. 59 .

Fig. 5.3: Part of the current structure of the instructions.

To enhance the usability of this part of the instructions, another structure is preterred (see also Fig. 5.2) namely:

Chapter containing the sections

r------l."Golfgebied- Band"

Afsteamin4g~------------------+-------2."Automatisch afstemmen"

~-----3."Handafstemming"

1r------1. "Voorkeuzetoetsen"

Prograameren~--------------~1 ~-----2."Automatisch programmeren"

Mono/Stereo ontvangst

Fig. 5.4: Altered and preferred structure of the instructions.

38

The new taxonomy with regard to the section "Afstemming" and "Programme­ren" is suggested for the following four reasons.

1) Functional differences In the first place: Tuning and programming are two functions that are functionally different from each other. These different functions should be presented and explained separately to enhance understandability.

2) Conceptual differences In the second place: Rext to the functional differences that exist between the "Tuning functions• and the "Programming functions": there is another reason to explain these functions as separate parts, namely the conceptual differences that exist between these functions.

The •Tuning functions" have the following conceptual aspects in common:

It is the user who selecte the stations. The selection criterium is the user' s own preferenee (i.e. the user decidee which station to attend to).

- The user selects one station each time the function is used. - Both functions are, more or leas, •archetypal' i.e.; they repreaent the

prototypical principles of a radio set. - The stations are not stored on the presets, neither automatically nor

manually.

The "Programming functions", thus, differ substantially from Automatic Tuning and Manual Tuning.

As can be seen in Fig. 5. 2, the section "Voorkeuzetoetsen" should be presented as a separate section in the chapter "Programmeren". Although the preset function is a programming function, it differs substantially from the Autostore function. The main differences between the Preset function (P) and the Autostore function (A) are:

(P} Stations are stored manually by the user. (A) The receiver •selects' the stations. (A) The selection criterion is the relativa signal strength of the

stations. (A) The receiver selects more than one station each time the function is

used. (A) The stations are automatically stored on the presets. (A) This function hardly bears any resemblance with any function of a

prototypical radio, since the internal processas which initiate the selection and storage of the five strongest stations are bidden and obscure to the average user.

Therefore, the Preset function is to be presented as a separate section in the chapter "Programming functions".

3) Knowledge aspects The third reaeon for the suggested-alteration is the fact that, in order to fully understand the section Autostore, the reader has to know what is meant by • PRESETS • and how to operate them. Although the information regarding the oparation of the Preset function is not yet presented to the reader, the section "Autostore" already informs the reader concerning the

39

fact that the five strongest stations are stored on the presets. Thus, the reader has to jump from the Autostore section to the section "Voorkeuze­toetsen" (page 58), in order to obtain a full grasp concerning the concept and oparation procedures of the preset function.

An incidental, but important effect of such an illogical structure could be that readers might loose interest in the instructions, since it takes too much effort to find the appropriate information.

4) Observatio:o.s duri:o.g the experiment Finally: During the experiment it became clear that the subjecte, in an attempt to find necessary information, looked for that information by means of reading the section headings (searching for information). Once a section was found that seemed to contain the needed information subjecte started to read the section, or partsof it (searching in information). This observa­tion has a number of consequences for the design of instructions.

The first implication of this finding is, on the one hand, that the section heading must be unequivocal with regard to the content of the section. The reader has to be guided by means of clear, meaningful, section headi.ngs, si.nce he does not know yet what information can be found in the subsequent sections. Readers will read that information first that seems to give answers to the questions they have. In order to locate the relevant i.nformation they will make use of section headings. On the other hand, section headings have to faci.litate differentiation from other section headings, that are either related or unrelated regarding content and the function concerned. If readers want to find information regarding Treble and Bass, the section heading "Voorkeuzetoetsen" tells them that the information they are looking for can not be found in that chapter. This section heading is unequivocal wi.th regard to the content of the section and, thus, helps to guide the reader in his searching proces.

The second implication is, that the information regarding each of the tune­tions of the car radio must be located at only one point in the instructions, namely that section that explains the working principles of that function. It must be avoided that readers have to jump from one section to another in order to find all necessary information. This means that each section has to be exhaustive regarding the information that can be found in it. This way, the instructions are more in accordance with the experiences readers have with other texts. New instructions can be easily checked with regard to the former demand.

The suggested changes in the current structure of the instructions (Fig 5. 2) facilitate the search proces as well as differentiati.on from other chapters. Additi.onally, the new chapters "Afstemming" and "Programmeren" cover the information that is included in these chapters more adequately.

40

GELUIDSWEERGAVE

ALGEMEEN

In deze autoradio worden de instellingen van het volume, de balans, de fader (voor/achter-regeling), de hoge en de lage ~onen langs elektronische weg geregeld.

Elke instelling gebeurt in stappen met de grote knop: Normaal functioneert deze als volumerege­laar. Drukt u echter op één van de toetsen BALANCE. FADER, TREBLE of BASS, dan verandert de functie van de grote knop in respectievelijk balans-, fader­of hoge- dan wel lage-tonenregelaar. Op het display verschijnen dan de letters 8 A L, F A 0, H l (high= hoog) of L 0 (low =laag). Met de grote knop stelt u nu de gekozen functie op het gewenste niveau in. Dit niveau wordt automatisch in het geheugen opgenomen. Korte tijd { 1 0 seconden) na de laatste instelling herkrijgt de grote knop vanzelf weer de functie van volumeregelaar. Als u echter binnen deze tijd op nogmaals dezelfde keuzetoets (b.v. 8ALANCE) drukt, dan wordt de grote knop onmiddellijk weer volumeregelaar.

Opmerking: Het is aan te bevelen om de grote knop tiJdens het autorijden alléén als volumere­gelaar te gebruiken.

5.3.1 The sectien "Algemeen11

The f irst sentence can convey more, relevant, in formation when the word a "volume, balans. fader, hoge en lage tonen regeling" are printed in bold capitals and the words "met de GROTE KNOP" are included. This way the sentence becomes more meaningful namely: volume, fader, baas and treble are adjusted electronically with the large knob. Sentence no. 5 can be omitted after the suggested change has been made.

Sentences no. 12 - 23 (page 54) contain information with regard to BALANCE, FADER, TREBLE and BASS. This information is, however, also given in the section "INSTELLEN VAN DE GELUIDSFUNCTIES' • It seems useful to leave all information regarding the sound functions out in this section and locate it in the latter section.

This also applies to the information regarding the volume. knob which should be located in the section "AAN/UIT -VOLUME".

Meaning and purpose of the remark "Opmerking" on line 24 of page 53 is unclear at first glance. This remark is probably a warning not to adjust FADER, BALANS, TREBLE and BASS while driving. Since there are nurnerous functions that require a great deal of effort and concentration, a more general warning focussing on such functions should be given here or else­where, if presentation of this information is considered necessary.

41

5.3.2 Adjustment of the sound functions

Table 4.21 (summary of the errors) shows that all subjecte omitted the use of the "large knob" while attempting to adjust the sound functions. After their initia! attempts failed, five subjecte started reading the instruc­tions. Only one subject discovered how to adjust the sound functions without reading the instructions. Two subjecte correctly solved the tasks after reading the information regarding these functions. 'l'he remaining three subjecte did not solve the task successfully, (unsuccessful is here defined as trying to solve the task by using an inappropriate function or sequence for more than three times) , although information in the section "Hoge en lage tonen" was read.

Observations during the experiment also illustrated that the subjecte were guided in their search by using the section headings, i.e., "geluidsregeling" (page 53), "Radio" (page 53), "Geluidsweergave" (page 54), "Aan/Uit - volume" (page 54), "Instellen van de geluidsfuncties" (page 54), "Hoge en lage tonen" (page SS).

These findings reemphasize the importance of locating related information in one section only. Since the section headings are used as a means to find relevant information, the information following the section heading has to contain all necessary information. Otherwise, readers have to start reading, (possibly unrelated) information in other sections, in order to get an answer on the questions they have. In this experiment five subjecte were able to adjust the sound functions only after reading the section "Algemeen", in which the missing information concerning the sound functions was located. This section ("Algemeen") seems very appropriate to include general information with regard to some overall system qualities of the DC685, that can enhance the development of a mental model. An important quality of the DC685 is the fact that, in order to initiate some of the functions, more than one button has to be used. Once the reader knows more about some of these higher order principles of the car radio, it will be easier to underatand, to apply, and to remember procedural information that is presented later in the instructions. This way the presented information can be fitted into the mental model that the reader has regarding the appliance.

Viewed in this manner, the instructions can be designed in such a way that higher order information as well as the procedural information is presented in a hierarchical structure in which necessary information is presented first and detail information later. This framewerk in which every "genera! section" only contains higher order information, concerning the appliance or its functions, can be adopted for all future Philips car-radio instructions.

42

AAN/UIT· VOLUME

• Zet de radio aan met toets ON.

• Regel het volume met de grote knop. Toelichting: Na het aanzetten hoort u het geluid met dezelfde instellingen als op het moment dat u de radio uitschakelde • . Was evenwel het volume op een te echter hoog niveau ingesteld dan zal, om redenen van veiligheid, het geluid op een lager niveau terugkomen dan toen u het apparaat uitschakelde.

Op het display kunnen verschijnen: a. functie-indicatie LOUD voor loudness b.1 veldsterkte-indicatie op FM, LG en MG (tot op

4 segmenten die naar links wijzen) b.2 indicatie voor de afspeelrichting tijdens het afspelen

(4 segmenten die naar links of naar rechts wijzen) b.3 indicatie tijdens het snelspoelen en tijdens MSS

• (linker en rechter knipperende pijlen) c. functie-indicatie ME/CR voor metal- of chromium

cassettes (allêén tijdens het afspelen van eer. cassette)

d. functie-indicatie CC voor DOLBY NR ingeschakeld (al/één tijdens het afspelen van een cassette)

e. zenderfrequentie, of de letters CAS (tijdens het afspelen van een cassette), of de letter •. C-·tijdens de wachttijd nadat een niet correcte beveiligings­code is ingevoerd

f. laatst bediende voorkeuzetoets (1 tot 5). tevens een indicatie (segmenten die na elkaar oplichten) gedu­rende de wachttijd. die volgt na het invoeren van een verkeerde beveiligingscode ·

g. indicatie AST voor AUTOS'rORE -h. golfgebieden: LW ( = LG), MW ( = MG), FM 1 of FM2 L de signaalindicatie STEREO (alléén op FM) j. functie...jndicaties INFO en OK k. signaalindicatie SK

5.3.3 The sectien "Aan/Uit - Volume"

This section contains a. picture of the display. However, neither the picture nor the text (points a.- k.) that accompanies the picture, is mentioned in this section. It seems useful to create a new section on behalf of this information. This way readers can locate the information concerning the display quickly, if necessary. This new section can be located either following the section "RADIO-ONTVANGST" (page 56), or pre­ceding the section "GELUIDSWEERGAVE" (page 54).

The information in this section was hardly read during the experiment. An explanation for this might be the fact that no tasks were given for which information of this section was necessary. However, it is surprising that none of the subjecte read more of this section that contains a lot of information regarding the display and its indications.

43

INSTELLEN VAN DE GELUIDSFUNCTIES

Balans

• Druk op de balanstoets (BALANCE). De frequentie op het display wordt vervangen door de letters 8 A L. Als u de grote knop verdraait verschijnt de instelling van de stereobalans. uitgedrukt in cijfers.

• Draai aan de grote knop en regel de balans tussen het linker en rechter kanaal. Wordt de grote knop niet binnen 10 seconden bediend dan wordt zijn functie vanzelf weer volumeregelaar. Het display toont weer de afgestemde frequentie.

Unker kanaal: Draait u de grote knop vanuit de middenstand linksom, dan toont het display eerst - 0 -. daarna 1 - -, 2 - - enz tot maximaal 9 - -.

Rechter kanaàl: Draait u rechtsom dan ziet u - - 1, • • 2, enz. tot maximaal - - 9.

Fader (voor/achter-regeling)

• Druk op de fader-toets (FADER) en regel de geluidsverdeling tussen de luidsprekers voorin en achterin met de grote knop. Het display toont daarbij de letters F A 0. Als u de grote knop draait toont het display de instelling uitgedrukt in

-cijfers ( 9 - - via - 0 - naar • - 9}.

Hoge en lagetónen

• Stel op gelijke wijze de hoge tonen (TREBLE) en lage tonen (BASS) in door op de desbetreffende keuzetoets te drukken. Hèt display toont respectievelijk H I of L 0. Opmerking: Bij het instellen van hoge en lage tonen toont het display een maximale waarde van 4, namelijk: 4 - -. 3 - -. 2 - :· , - -. - 0 -. - - , • - - 2, - - 3, - - 4.

5.3.4 The sectien "Instellen van de geluidsfuncties"

Directly following the section heading, the overall operating principles of the sound functions have to be explained. The following introductory information, which is partly already included in the section "Algemeen", is considered essential;

l) Adjustment takes place by subsequently pushing one of the four sound function controle and turning the "large knob".

2) The level of the adjusted function is automatically stored in memory for the stations stored on the preset buttons, in the wave range being tuned to.

3) How the LARGE KNOB becomes VOLUME CONTROL again (this information is not given in the section "Instellen van de geluidsfuncties").

Since readers start with searching ~ informatlon and then proceed with searching in information, the following subsections "Balans", "Fader" and "Hoge en lage tonen" must each contain complete itemized operatien steps, for the following reason. In the section "hoge en lage tonen" the reader is advised to adjust Treble and Bass "in the same way". All five subjecte read this sentence and stroke off to read the sections "Loudness" and "Algemeen". None of the subjecte searched for the missing information in the p~eceding sections "Fader" or "Balans", but started to search in the sections "Loudness" and "Algemeen". one of the subjecte commented upon the situation: "Ik begin maar even helemaal vooraan te lezen bij Algemeen, dan kom ik het wel tegen denk ik". The fact that the missing information was not looked up in the two preceding sections could be explained by the fact that the procedural information in these sections does not give a clear overview of the procedural steps at first sight. Possible reasons for this are: The information concerning the adjustment of Balance, which exists of two procedural steps, is divided over two pages. On the other hand, the information concerning Fader exists of only one procedural step.

The section "Balans" is followed by two pictures of the radio that can easily be replaced with one picture, since (nearly) identical information is presented in both pictures.

It is interesting to see (Table 4.13 - 4.17; marked text) that none of the subjecte read information with regard to "BALANS", although all subjecte successfully adjusted it. Apparently, once ~t is known how to adjust Treble and Baas, it is easy to adjust Balance. This does not mean that it is satisfactory to explain only one of the sound functions e.g. as an example. Readers differ concerning the questions they have regarding the subsequent functions. one reader might want to know how to operate Balance, and will therefore start reading the information concerning Balance. Another reader might want to know how to adjust Treble or Baas and will therefore start reading all information concerning Treble and Bass. An implication of these facta is that these sections should be redesigned in a more structured way using the current, adequate, information. The information can be presented in such a way, that each function is fully explained and all functions are explained in the same manner. This way, readers do nothave to return-to an earlier section in order to find the wanted information.

44

LOUDNESS

0 goJr llOrn 0

0 c ;=oor !

,;, ... .-...-...... , ~:sas;. - mor .............. ;;

• Druk. indien gewenst, op de toets LOUD. Het display toont LOUD.

!

• Druk nogmaals op toets LOUD als u de loudntlSS functie wilt uitschakelen. Als de loudness-functie is ingeschakeld worden de hoge en lage tonen meer versterkt Het effectvan de loudness is afhankelijk van de instelling van de toonregelaars.

AUTOMATISCH AFSTEMMEN omhoog - of omlaag

• Druk even op één van de afstemtoetsen omhoog (-} of omlaag (-) en u ontvangt na korte tijd een station. • Druk nogmaals op dezelfde toets en u ontvangt even later het volgende station in de richting van·de zoekafstemming. - De frequenties op het display veranderen in stappen van 50 kHz voor FM en 9 kHz voor MG en 1 kHz voor LG. -Als de hoogste freQuentie is bereikt (b.v. voor FM: 108 MHz) gaat het afstemmen verder vanaf de laagste freQuentie (voor FM: 87,5 MHz) en omgekeerd. - Het automatisch zoeken naar zenders gebeurt in alle frequentiebanden op drie zoekniveaus. Eerst zoekt de radio naar sterke zenders. Worden geen sterke en geschikte zenders gevonden. dan schakelt het afstem· systeem over op een lager z.oekniveau. Nu worden minder sterk'!! zenders afgestemd, enz.

Als. na enige tijd (mëer dan 80 seconden) weer een ván de afstemtoetsen wordt bediend, begint het automatisch afstemsysteem opnieuw naar sterke zenders te zoeken. - Stemt het zenderzoeksysteem af op een zender die, voor het gekozen golfgebied, reeds onder één van de voorkeuzetoetsen is geprogrammeerd, dan toont het display ook het nummervan de desbetreffende voorkeu­ze toets. Opmerking: Het automatisch afstemmen kunt u met behulp van een schakelaar ook op afstand bedienen, echter alleen in de opwaartse richting. (Zie INBOUWVOORSCHRIFl).

5.3.5 The section "Loudness"

Three subjecte asked the experimenter during the experiment what the effect of this function was. Information regarding the effect of the loudness function is given at the end of the section Loudness. In order to understand more about the function, this information should be located in the beginning of the section, directly following the section heading.

5.3.6 The section "Automatisch afstemmen"

The text (small letters) following "automatisch afstemmen" contains a ? printing error: 50 ~z should be 50 HHz. o

Four subjecte read information regarding the function Automatisch afstemmen. The remaining two subjecte managed to tune to stations without reading. Table 4.19 shows that 2 subjecte uttered remarke regarding Automatic tuning (assumptions 1 and 4). These remarke were made while using Automatic tuning. These subjecte more or less thought that the function Automatic tuning could be used for listening to preselected stations. Appa­rently, for these subjecte Automatic Tuning bears little resemblance with tuning functions that are familiar to the subjecte (i.e, tuning knobs that have to be rotated).

In Fig. 4.2 (progression graph) it can be seen that in the FM part all subjecte wrongly used Automatic tuning (more than three times) while Manual tuning should be used in order to tune to a specific frequency. As the subjecte came to realize that Automatic tuning was an inappropriate function to use they started reading the adequate information in the section "Handafstemming".

In the AM part of Fig. 4.4 it can be seen that four subjecte used Automatic tuning instead of Manual tuning. This time, Automatic tuning was used to tune to a station (frequency) near the frequency that had to be tuned to. This deviation should therefore be explained as a shortcut: an attempt to tune to the wanted frequency in a quicker way. This observation shows that these subjecte formed a mental model of the working principles of both functions since they deliberately used an "inappropriate" function as a means to reach the intended goal.-

Since Automatic tuning is used more often than Manual Tuning (Winters, 1988), some information, directly following the section heading, concerning the working principles of this function can enhance the understanding.

It is very important to phrase the information in such a way that there is a better fit between the text (words) and the concept (the idea) than there is now. In this section ("Automatisch afstemmen"), however, the expressions •afstemmen• (tuning) and 'zoeken• (selecting) are used as synonyms. Even the contamination "zoekafstemming" is used in the text (page 56). A conse­quent use of the term "afstemmen" (tuning) is to be preferred.

45

HANDAFSTEMMING -en-

00 00

0 Opmerking: De handafstemming wordt hóofdzakelijk gebruikt om stations te programmeren waarvan de frequentie bekend is.

• Druk kort op beide afstemtoetsen - en -tegelijkertijd. De functie van de toetsen verandert van 'automatische afstemming' in 'handafstemming'.

Stap voor stap handafstemmen • Druk nu kort op één van de toetsen- of-. De frequentie verandert met één stap omhoog of omlaag. Eén stap is 50 kHz voor FM en 1 kHz voor MG en LG.

Snel handafstemmen • Houd één van de afstemtoetsen - of -ingedrukt. Na 1 seconde wordt de frequentieband snel afgetast totdat u de toets loslaat. De radio is tijdens deze handeling stil. - Na de hoogste frequentie volgt de laagste frequentie en omgekeerd De afstemtoetsen krijgen weer hun functie 'automatisch zenderzoeken' terug wanneer u: 1. niet binnen 50 seconde op de afstemtoetsen drukt. 2. de radio uit- en daarna weer aanzet. 3. kort op BAND-keuzetoets. op één van de voorkeuze­

toetsen (1- 5) of op de AUTO STORE-toets drukt Opmerking: Als u de handafstemming kiest wordt de INFO-stand uitgeschakeld.

5. 3. 7 The sectien ''Handafstemming"

Some information about the working principles directly following the section heading should be included.

In the text, the expression "programmeren" Handafstemming wordt hoofdzakelijk gebruikt meren •••••• "). This expression is confusing for information concerning programming yet, since;

(programming) is used ("de om stations te program­

the reader who has not read

- The user does not, in fact, program a station, but is tuning to a station.

- Confusion with the former section "Automatisch programmeren" is likely, since the reader is not capable yet of differentlating the concepts "Programming of presets" and "Programming with Autostore".

Readers often find it difficult to understand expressions as: "not longer than" etc. Line 23 of this section says: "De afstemtoetsen krijgen hun functie •automatisch zenderzoeken• terug wanneer U niet binnen 50 seconden op de afstemtoetsen drukt". ( ••• back if you do not operate them within 50 seconde). This sentence bacomes much easier if it is actively repbraeed as: " De afstemtoetsen krijgen hun functie •automatisch afstemmen' terug wan­neer U 50 seconden wacht" ( ••• wait for 50 seconde ••• ).

46

VOORKEUZETOETSEN (1 - 5)

Programmeren van de voorkeuzetoetsen

•c )1 a. Kies het gewenste golfgebied (LG, MG,

FM1 of FM2) met de BAND-keuzetoets. b.Stem nauwkeurig af op een gewenste

zender met behulp van: . SEARCH (Automatische afstemming) of HANDAFSTEMMING.

c. Programmeer de gevonden zender als volgt: Druk zó lang op de gewenste voorkeuze­toets (b.v. toets 1) tot u een tweetonige piep ~ hoort als teken dat de zender­frequentie in bet geheugen is opgenomen. Op het display verschijnen: Het golfgebied, de freQuentie en het toetsnummer waaronder u de zender hebt geprogrammeerd. Opmerking: Als u korter dan 2 seconde ·op de .voorkeuzetoets drukt wordt de frequentie opgeroe­pen die de vorige keer was geprogrammeerd.

• P~ogrammeer op dezelfde wijze de volgen­de voorkeuzetoets.

• Herhaal bovengenoemde handelingen voor de overige golfgebieden.

Opmeri<ing: De INFO-stand kan tegelijk worden meegeprogrammeerd. Zie hoofdstuk: VERKEERS­INFORMA TIE - I"!,FO-stand meeprogrammeren.

Bediening van de voorkeuzetoetsen

Nadat de radio is geprogrammeerd behoeft u slechts: a. Op de BAND-toets te drukken om het

·gewenste golfgebied in te stellen. b.Op één van de voorkeuzetoetsen (b.v.

toets 4) te drukken.

Opmerking _ U kunt een zender van de ene voorkeuzetoets op een andere programmeren (b.v. van toets 1 op toets 3) met behulp van 'handafstemming' en wel als volgt: 1. Kies de gewenste zender door op één van de

voorkeuzetoetsen (b.v. toets 1) te drukken. 2. Druk kort op beide afstemtoetsen (-en-) tegelijker­

tijd voor het instellen van de handafstemming. De voorkeuze-indicatie verdwijnt uit het display.

3. Druk zó lang op de gewenste voorkeuzetoets (b.v. toets 3) totdat u een tweetonige piep JJ hoort. Deze zender is nu onder deze toets geprogrammeerd.

De tussenstap met de stand 'Handafstemming' is nodig om ongewenst programmeren te voorkomen wanneer u per ongeluk te lang op éénvan de voorkeuzetoetsen zou drukken.

5.3.8 The section "Voorkeuzetoetsen"

some inform•tion about the working principles directly following the section heading should be included. Table 4.19 contains a number of assumptions regarding the preset buttons. Apparently, it is not clear that each preset can contain one station on each of the four wave bands and that programming an FM station on preset 1 does not delete the MW an LW stations that were already stored on preset 1. Consequently, this section has to be rewritten and should contain introduc­tory information regarding the fact that on all 4 wave bands, five stations can be programmed on the preset buttons. The rest of this section shoul.d be presented in a more structured form, in which each of the oparating steps is shortly explained and all subsequent sequence steps are placed near to each other.

47

AUTOMATISCH PROGRAMMEREN (AUTO STORE)

AUTO STORE werkt zowel op de FM-band als op de MG-band. Het is een uitgebreid zenderzoeksysteem, waarmee u met èén druk op de AUTO STORE-toets vijf extra zenders op FM en MG automatisch kunt selec­teren en direct onder de voorkeuzetoetsen program­meren. AUTO STORE is uitermate nuttig als u zich in een gebied bevindt, waarvan u de zenderfreQuenties niet kent. bijvoorbeeld tijdens uw vakantie. of zakenreis. Met AUTO STORE kunt u dan de vijf sterkste zenders van dat gebied automatisch selecteren zonder hun frequenties te kennen.

Programmeren met AUTO STORE

00 00

0 a. Kies eerst de FM-band of de MG- met de

BANO-keuzetoets. b. Druk langer dan 2 seconden op de AUTO

STORE-toets om in de AUTO STORE­programmeerstand te komen van het gekozen golfgebied. U hoort een twee­tonige piep Jj.

- In het display knippert de indicatie AST en de frequentie-aanduiding verdwijnt eruit.

Als de autoradio in de AUTO STORE- program­meerstand staat valt het geluid van de radio weg, het galtgebied wordt snel afgetast en de vijf sterkste zenders worden automatisch onder de vijf voorkeuze-toetsen geprogrammeerd. . Telkens als een zender wordt geprogrammeerd, toont het display het nummer van de vijf voorkeuzetoets en de frequentie van het station. Als alle zenders geprogram­meerd zijn schakelt de radio terug naar de AUTO STORE- bedieningsstand, wat aangeduid wordt door een twee-tonige piep Jj_ Vervolgens hoort u de sterkste zender in dit gebied, die

op voorkeuzetoets 1 met AUTOSTORE is geprogram­meerd. Hebt u de LG-band gekozen, dan hoort u een fouttoon. • Druk nu één maal (voor MG) of twee maai (voor FM) op de BAND-toets.

• Kies de andere band (MG of FM) met de BAND-keuzetoets. • Druk opnieuw op de AUTO STORE-toets totdat de AST-indicatie gaat knipperen. Nu worden vijf stations .Yan het andere golfgebied geprogrammeerd.

Opmerkingen - Als onder bepaalde omstandigheden geen vijf zenders worden gevonden, dan worden de overgebleven voorkeuzetoetsen (b.v. 4 en 5) geprogrammeerd met ·ooo·. Als u later èén van deze toetsen met '00' kiest dan valt de radio stil. -Wanneer een ongewenste zender is geprogrammeerd {b.v. als een zender op toets 4 hetzelfde programma heeft als die op toets 2), kunt u op toets 4 opnieuw een andere zender programmeren door zo lang op toets 4 te drukken dat de AST-indicatie gaat knipperen. U hoort een tweetonige piep Jj. ·- . . - Als een zender met verkeersinformatie is gevonden, wordt de INFQ-stand automatisch meegeprogram­meerd. (Zie hoofdstuk: VERKEERSINFORMA TlE).

Bedienen van AUTO STORE

·· Na het programmeren behoeft u slechts: a.De FM- of de MG-band te kiezen met

BANO.:keuzetoets. b. Kort op AUTO $TORE-toets te drukken; het

display toont de indicatie AST. c.Op één van de voorkeuzetoetsen (b.v.

toets 4} te drukken; U ziet op het display de frequentie en het nummer van de ingedruk: te voorkeuzetoets.

U kunt de AUTO STORE-bedieningsstand opheffen door op de BAND-toets te drukken.

Opmerkingen - Wilt u echter een zender programmeren, waarop u met automatisch zenderzoeken of met de hand hebt af­gestemd. druk dan langer op èén van de voorkeuze­toetsen tot u een tweetonige piep hoort .Q; de radiO verlaat dan de AUTO STORE-stand. De zenderwordt nu

onder een van d~ voorkeuz~toetsen 1n het gekozen golfgebied geprogrammeerd. - AUTO STORE zenders kunnen als volgt worden overgezet op de normale MG- en FM-band: • Kies een 'AUTO STORE'-zender. • Druk kort en tegelijkertijd op beide voorkeuzetoet­sen tegelijk. Het voorkeuzetoets-nummer verdwijnt, maar de frequentie in het display verandert niet • Druk op een voorkeuzetoets (b.v. toets 1) totdat u een tweetonige pieptoon hoort Jj, De radio schakelt nu over van de z.g. 'onderbroken­

. AUTO STORE' -stand over naar de normale MG- of FM 1-en FM2-band en de zender wordt onder de gekozen voorkeuzetoets geprogrammeerd.

5.3.9 The sectien "Automatisch programmeren"

The introductory text is too long. A·new, shorter, text should contain the following information:

Short explanation of the effect and working principles of the function Autostore.

- Autostore can not be used at the LW-Band (this formulation is easier to comprehend than the current sentence of this section).

5.3.10 The sectien "Programmeren met Autostore"

The experiment clearly shows that this section was the most difficult one to understand. The marked text (copy of the instructions), in chapter 4 indicates that nearly all the text is read. Three subjecte managed to program Autostore correctly after reading the instructions. The remaining three subjecte did not succeed, although an extensive amount of information was read. As Table 4.19 and 4.20 indicate, the concept bebind Autostore is difficult to understand. one subject thought that Autostore is merely a function that "fellows" a station over a long distance by switching to another frequency once the field strength reduces. Two subjecte thought that once the Auto­store stations are found they remain on the presets permanently, displacing the stations that were programmed aarlier by the user. One subject thought that programming an FM station on preset 1 would delete the AM station on preset l. In other words, the five preset buttons can only contain five stations. These, wrong, assumptions will interfere with understanding the concept of Autostore.

In the sectien "Programmeren met Autostore" the concepts "programming mode" and "operation mode" are introduced. Since the exact meaning and prin­ciple& of these concepts are not further explained, their meaning and relevanee for the reader probably remain unclear and, consequently, can reduce the understandability. Since a thorough explanation of these concepts would become too elaborate, they better be left out.

The text contains some errors and indistinct passages that make the operatien more difficult:

Page 56: line 38 of the right column should be supplemented: "De sterkste zender wordt nu onder voorkeuzetoets l geprogrammeerd, de volgende (sterkste) zender onder voorkeuzetoets 2 enz".

- Page 57: line 6 of the right column contains an error: "Druk kort en tegelijkertijd op beide voorkeuzetoetsen tegelijk". The word "Voorkeuzetoetsen" has to be replaced with "afstemtoetsen".

In order to reach more "transparency", the oparation steps for programming and oparating Autostore should be presented in a short form and should be placed near to each other. The eperating steps should be presented in a clear and structured format. Due to the vague text, all the subjects omitted pressing the Autostore knob briefly in order to listen to the found Autostore stations (Fig. 4.6: Pro­graasion Graph 6). Consequently, all they heard was noise, coming from the. radio. As a reaction to this, four subjecte preseed the Autostore button again for more than 2 seconde and thus started the programming cycle.

48

GEB R UIKSAANWJJZING

Sla tijdens het lezen van de gebruiksaan­wijzing ook pagina 3 uit.

OVERZICHT VAN BEOIENINGSORGANEN

GELUIDSREGELING

CD Aan/uit-schakelaar (ON) ® Keuzetoets voor voor/àchter-regeling

(FAD) 0 Keuzetoets voor balansregeling (BAL) 0 Keuzetoets voor lage tonenregeling

(BASS- LO) ® Keuzetoets voor hoge to!îenregeling

(TREBLE- Hl) ® Volumeregelaar, ook regelaar van fader,

balans, hoge en lage tonen (LEVEL-VqL) 0 Loudness-toets (LOUD)

RADIO

® Digitale schaal (display) Beschadig het display niet door erop te drukken of te wrijven

® Toetsen voor automatisch zenderzoeken en handafstemming - = frequentie omhoog .... = frequentie omlaag Ook gebruikt voor intoetsen van de bevei­ligingscode

@ Voorkeuze/programmeenoetsen (1 - 5} -® INFO-toets voor verkeersinformatie @ OK-toets voor verkeersberichten-identifi-

catie @ AUTO STORE op MG en FM @ Golfgebiedschakelaar (BAND) @ Keuzetoets voor radio of casse~espeler

(MODE)

CASSErrESPELER

@Toets voor Music Sensor System (MSS) om het vorige of het lopende stuk muziek te herhalen als toets « wordt ingedrukt, of om het volgende stuk muziek af te spelen als toets » wordt ingedrukt

@ Aan/uit schakeiaar voor Dolby(g 8 NR systeem (DO)

@ Keuzeschakelaarvoor 'Metai/Chromium'­en 'Ferro'-cassettes (ME/CA)

@ Cassette-opening @ Toets voor omkeren afspeelrichting (C >)en

uitwerpen van de cassette :::: @ en @ Toetsen voor snelspoelen ( « en »)

De richting van het snel vooruit- en , terugspoelen hangt af van de momentele afspeelrichting zoals het display aangeeft.

® Ruisonderdrukkingssysteem gefabriceerd onder li­centie van Dolby Laboratorles Ucensing Corporation. Het woord 'Dolby' en het symbool van de dubbele D zijn handelsmerken van Dolby Laboratories Ucensing Corporation.

5.4 Names of knobs and functions

Table 4. 23 contains the different names of the knobs and functions. The "unambiguity" demand also applies to the names given to knobs and functions. Differing names wil! slow down the learning proces of the reader. Although the names that are used in the instructions more or lees look alike, it should be prevented that a tunetion is referred to with another name.

Especially in complex appliances, differing names might cause the reader to think that a different name refers to a related, but slightly differing function or knob of the appliance. Moreover, it is not unthinkable that a function name which differs from the name in, for instanee the index, might not be recognized as such by the reader. All mentioned effects could also annoy the reader and thus lower the interest of reading the instructions at all.

Name in "Overzicht Name in the instructions van de bedienings-organen"

Toetsen voor automa- Search tisch zenderzoeken Afstemtoets •

Afstemtoets ,. Afstemtoets omhoog Afstemtoets omlaag Toets • Toets " omhoog omlaag

Volumeregelaar Grote knop (in the section "AAN/UIT -Volume" as wel! as in the sectien "Instellen van de geluidsfuncties"

Golfgebiedschakelaar BAND-keuzetoets BAND-toets

Keuzetoets voor Balanstoets balansregeling Balans

Keuzetoets

Keuzetoets voor Fadertoets voor/achter Toets fl:lder regeling (FAO)

Loudnesstoets Toets loud

Keuzetoets voor hoge- Toonregelaar en lage tonen rege-ling

-Table 4.23: The left column contains the names of knobs and functions

from the sectien "overzicht van de bedieningsorganen" (page 53). The right column contains the names of these knobs and functions from the text.

49

EXPERIMENT II

6. Summary of Experiment II

In Experiment II the ease of use of the DC685 cassette receiver was evaluated under an experimental simulation of traffic conditions.

Six trained subjecte were assigned to three experimental conditions. In the first condition, subjecte concentrated on the performance of a number of radio control tasks on the cassette receiver. In the second condition, subjecte concentrated on the performance of a visual reaction time task which was presentedon a computer screen. In the third and final condition, subjecte concentrated on the reaction time task as well as on the performance of the radio control tasks on the cassette receiver. In this final condition, the correct and adequate reaction to the reaction time stimuli had priority.

To a certain extent this experiment bears resemblance with driving a car. As in driving a car, the attention of the subjecte was primarily focuseed on a visual task. Moreover, as in driving a car the subjecte had to react quickly and adequately to a visual task.

The t3me needed to perform the radio control tasks was measured in the first as well as in the final experimental condition. In both conditions, the subjecte performed the same radio control tasks. By comparing the time measures of these radio control tasks in both experimental conditions it became possible to investigate to which extent the performance of the various operatien sequences was affected in the Dual Task condition.

It can be concluded that the extent to which the operatien sequences were affected by the Dual Task condition is depending on the necessity of obtaining visual feedback from the car radio. In othe~ words, the eperation sequences in which the subjecte had to look at the display of the car radio for visual feedback were affected most by the Dual Task condition.

Next to the presence or absence of a visual component in an operatien sequence the number of eperation steps that constitute an operatien sequence bas an effect on the speed with which the sequence is performed: the more eperation steps the sequence contains, the more the operatien speed is slowed down.

Finally, it seems that the increase of the time needed to perferm the eperation sequences in the Dual Task condition is non-linear. In other words, it is well possible that doubling the number of operatien steps in an eperation sequence results in an eperation time that is more than doubled. This finding might be explained by an altered strategy of the subjecte in the more lengthy eperation sequences.

51

7. Metbod of research

7.1 Introduetion

In the following experiment (EXPERIMENT II) it will be investigated how the oparation of various functions of the Philips DC 685 car radio is affected, while the attention of the user is primarily focuseed on another, visual, task.

In one of the three experimental conditions of this experiment the subjecte were asked to perform two tasks simultaneously: a primary task as well as a secondary task. The primary task consisted of a reaction time task, visually presented on a computer screen. The secondary task consisted of a number of radio control tasks.

In order to reapond quickly and correctly to the stimuli (the primary task) that were presented on the computer screen, the subjecte had to be constantly alert. Especially since the subjecte were asked to regard the primary task as their most important task.

The mental demands that were placed upon the subjecte in the primary task bear some resemblance with the mental demands that are placed upon the driver of a car with regard to the following aspect:

As in driving a car, where the driver has to be constantly alert in order to reepond quickly and adequately to traffic lights, traffic tables, etc., the subjecte had to be constantly alert as well in order to reapond quickly and adequately to the stimuli that were presented on the computer screen.

In other words: the driver of a car, as well as the subjecte in the current experiment, focus part of their attention on a visual task. This permanent alertness that is required hinders the operatien of the car radio.

Since the car radio has to be operated under circumstances that are cited above, it is crucial that the various functions can be operated relatively easy. As stated earlier, by introducing the radio control tasks as a secondary task, it is possible to investigate, in an experimental setting, in what way the operatien of the various functions of the car radio is affected.

This does ~ mean that in this experimental setting it can be investigated how the oparation of the car radio functions is affected while driving a car. It is merely possible to investigate what functions or oparation sequences are affected most or least, while the subjecte focus part of their attention on a visual task.

7.2 The secondary task technique

Normally, the secondary task technique is used for different reasons than in the current experiment. By measuring how successful a secondary task is performed it is possible to estimate the workload of the primary task. Mental workload can, more or less, be described as the mental demands or the amount of mental effort that is placed upon someone performing a certain task.

52

For instance, an operator of a machine bas a limited capacity to perform bis (primary) task. The mental demands that are placed upon him should not exceed his capacities. If bis capacities are exceeded, breakdowns in his performance will occur. Even if the demands are not exceedinq bis capacities it is important that the machine is desiqned in such a way that there is a sufficient marqin of residual capacity or resources. otherwise, unexpected failures of the machine can not be handled satisfactory by the operator. By measurinq the performance in the secondary task, the residual capacity or resources can be determined. Throuqhout the years a number of secondary tasks have been proposed and employed to assess the residual capacity left while performinq primary tasks. Some of these tasks will be briefly described here (see Wickens, 1984 for a more detailed overview.).

Rhythmic tapping or interval-production task. The subject is asked to maintain a constant rate of finqer tappinq. It is assumed that primary task demands will disrupt the ability of constant finqer tappinq. The primary task workl.oad is reflected by increased variability of the intertap interval.

Random number generation. Subjecte are asked to qenerate a stream of random diqits. The deqree of randomness deelinas if the workload of the primary task is increased. As the workload increases, subjecte beqin to qenerate repeatinq sequences such as "123 123 123".

Probe reaction time. Subjecte are asked to react to an unpredictable stimulus. As the primary task demands more resources, subjecte react slower to the probe taak.

7.3 The experimental conditions

As stated in section 7.1, the current experiment consisted of three experimental conditions. Precedinq these three experimental conditions subjecte were trained reqardinq the oparation procedures of the car radio (see section 7.4). The three experimental conditions were:

1) the Radio Sinqle Task condition (RST), in which subjecte only concentrated on the performance of a number of control tasks on the cassette receiver (see section 7.5),

2) the Reaction Time Sinqle Task condition (RTST), in which subjecte only concentrated on the performance of a reaction time task ( see section 7. 6) ,

3) the Radio Dual Task condition (ROT), in which subjecte concentrated on the reaction time task as well as on the performance of the control tasks on the cassette receiver. In this condition, the correct performance of the reaction time tasks had priority (see section 7.7).

The subjecte were assiqned to all three conditions, which makes this an experiment with a repeated maasurement deaiqn. First, subjecte repeived the training-. Next, they were assiqned to the Radio Sinqle Task (RST) condition, to the Reaction Time Sinqle Taak (RTST) condition and finally to the Radio Dual Taak (ROT) condition. The control taaks that had to be performed in the Radio Sinqle Taak (RST) condition and Radio Dual Task (ROT) condition are summed in Tables 7.1, 7.2, 7.3 and 7.4.

53

\

7.4 The training, given to the subjects

All subjecte received a training at the beginning of this experiment. The goal of this training was twofold.

1) To train the subjecte in such a way that they all had comparable experience regarding the oe 685 cassette receiver at the offset of this experiment. The subjecte were expected to be able to perferm the control tasks below a fixed time criterion (5 seconde) after completion of the training.

2) To train the subjecte with regard to percaiving and remembering the control tasks. Since short presentation of these, rather complex, control tasks was an important factor, the subjecte had to be trained in quickly reading and remembering the one- two- or three-word sentences within the exposure time of 3 seconde.

Fig. 7.1 illustrates how these tasks were presented on the computer screen. The right column of Table 7.5 contains some examples of the abbreviated form in which these control tasks were represented.

.A.AN' Fl.U

ZENDE:S.

During the training, the subjecte received an explanation in which the experimenter explained the working principles of the cassette receiver. In this explanation, all functions of the car radio were explained and shortly demonstrated. This explanation lasted about fifteen minutes and the subjecte were allowed to ask questions.

Fig. 7.1: Presentation of FM task nr.1.

Next, the control tasks (as stated in the left columns of Tables 7.1 - 7.4) were demonstrated on the radio by the experimenter. Additionally, the abbreviated representation of the control tasks (Table 7.5) was demonstrated and explained to the subjecte. Finally, the subjecte were trained in reading and performing the abbreviated control tasks. The subjecte started the training with the FM control tasks, one by one, three times in a row

(Table 7.1).

Next, the AM control tasks (Table 7.2) were trained (one by one, three times in a row) follÖwed by the [FM/AM]1 and [FM/AM}2 control tasks (Tables 7.3 and 7. 4). Next, in the final stage of the training session the subjecte performed the FM control tasks, followed by the AM control tasks, the [FM/AM J 1 control tasks and the {FM/AM)2 control tasks. Table 7.1 illustrates the sequence of the substages in the training session.

1. FM control tasks ( three times in a row) 2. AM control tasks (three times in a row) 3. (FM/AM]1 control tasks (three times in a row) 4. [FM/AM}2 control tasks (three times in a row) s. FM control tasks (once and directly followed by)

AM control tasks (once and directly followed by) [FM/AM)l control tasks (once and directly followed by) [FM/AM)2 control tasks (once)

Table 7.1: Sequence of the substages in the training session.

54

Directly following the final substage of the training session the experimenter checked if the subjecte performed the tasks below the time criteria that were set. These time criteria were based on the performance of two "test subjecte" during pilot tests of this experiment. During these pilot tests, the "test subjecte" performed the FM and AM control tasks, on the average, within 4 seconde. The [FM/ AM J 1 and [FM/AM] 2 control tasks we re, on the average, performed within 7 seconde.

The purpose of setting and verifying these time criteria was mainly to see if reasonably could be expected that the subjects were able to perform the control tasks under time pressure.

55

Control tasks on the FM Band

1. Switch on the radio tune to a station on the FM Band (The wave range was set to the AM Band by the experimenter at the onset of this control task)

ON /BAND /SEARCH

2. Tune to a station SEARCH /VOLUME change the volume level

3. Tune to a station SEARCH /LOUDNESS push the Loudness button

4. Push the Autostore button briefly AUTOSTORE /PRESET 4 listen to the found station on preset 4

5. Tune to a station change the Bass level (subjecte were asked to turn the large knob to the left)

6. Tune to a station change the Treble level (subjecte were asked to turn the large knob to the left)

7. Tune to a station change the Balance level (subjecte were asked to turn the large knob to the left)

SEARCH /BASS /LARGE KNOB 4--

SEARCH /TREBLE /LARGE KNOB 4--

SEARCH /BALANCE /LARGE KNOB 4--

8. Tune to a station SEARCH /BASS /LARGE KNOB -0-adjust the Bass level back to neutral

9. Tune to a station SEARCH /TREBLE /LARGE KNOB -0-adjust the Treble level back to neutral

10. TUne to a station adjust the Balance level back to neutral

ll. Tune to a station programme with Autostore

12. Tune to a station switch off the radio

SEARCH /BALANCE /LARGE KNOB -0-

SEARCH /AUTOSTORE l

SEARCH /OFF

Xable 7.2: Control tasks that had to be performed on the FM Band (left column). The right column contains the correct functions that had to be used.

56

Control tasks on the AM Band

l. Switch on the radio Listen to the station on preset l

2. Listen to the station on preset 2 change the volume level

3. Listen to the station on preset 3 push the Loudness button

4. Push the Autostore button briefly listen to the previously stored station on preset 4

5. Listen to the station on preset 1 change the Bass level (subjecte were asked to turn the large knob to the left)

6. Listen to the station on preset 2 change the Treble level (subjecte were asked to turn the large knob to the left)

7. Listen to the station on preset 3 change the Balance level (subjecte were asked to turn the large knob to the left)

8. Listen to the station on preset l adjust the Bass level back to neutral

9. Listen to the station on preset 2 adju9t the Treble level back to neutral

10. Listen to the station on preset 3 adjust the Balance level back to neutral

11. Listen to the station on preset 4 programme with Autostore

12. Listen to the station on preset 5 switch off the radio

ON /BAND /PRESET l

PRESET 2 /VOLUME

PRESET 3 /LOUDNESS

AUTOSTORE /PRESET 4

PRESET l /BASS /LARGE KNOB 4--

PRESET 2 /TREBLE /LARGE KNOB 4--

PRESET 3 /BALANCE /LARGE KNOB 4--

PRESET 1 /BASS /LARGE KNOB -0-

PRESET 2 /TREBLE /LARGE KNOB -o-

PRESET 3 /BALANCE /LARGE KNOB -o-

PRESET 4 /AUTOSTORE l

PRESET 5 /OFF

Table 7.3: Control tasks that had to be performed on the AM Band (left column). The right column contains the correct functions that had to be used.

57

control tasks on the FM and AM Band [FM/AM]l

1. Switch on the radio and tune to a station on the FM l Band

2. Listen to the AM station on preset 1

3. Tune to a station on the FM 1 Band change the volume level

4. Listen to the AM station on preset 2 change the volume level

5. Listen to the AUTOSTORE station on preset 1 on the FM l Band

6. Listen to the AUTOSTORE station on preset 3 on the AM Band

7. Listen to the FM 1 station on preset 2 push the Loudness button

8. Listen to the AM station on preset 4 push the Loudness button

9. Tune to a station on the FMl Band change the Balance level (subjecte were asked to turn the large knob to the left)

10. Listen to the AM station on preset 1 change the Balance level (subjecte were asked to turn the large knob to the left)

11. Tune to a station on the FMl Band and change the Treble level (subjects were asked to turn the large knob to the left)

ON /BAND /SEARCH

BAND /PRESET 1

BAND /SEARCH /VOLUME

BAND /PRESET /VOLUME

BAND /AUTOSTORE /PRESET 1

BAND /AUTOSTORE /PRESET 3

BAND /PRESET 2 /LOUDNESS

BAND /PRESET 4 /LOUDNESS

BAND /SEARCH /BALANCE I LARGE KNOB 4--

BAND /PRESET 1 /BALANCE I LARGE KNOB 4--

BAND /SEARCH /TREBLE /LARGE KNOB 4--

Table 7.4: Control tasks that had to be performed on the FM and AM Band (left column). The right column contains the correct functions that had to be used.

58

control tasks on the FM and AM Band (FM/AM]2

12. Listen to the AM station on preset 2 change the Treble level (subjecte were asked to turn the large knob to the left)

13. Tune to a station on the FM1 Band change the Bass level (subjecte were asked to turn the large knob to the left)

14. Listen to the AM station on preset 3 change the Bass level •

. (subjecte were asked to turn the large knob to the left)

15. Tune to a station on the FM1 Band and adjust Balance back to neutral

16. Listen to the AM station on preset 1 and adjust Balance back to neutral

17. Tune to a station on the FMl Band and adjust Treble back to neutral

18. Listen to the AM station on preset 2 and adjust Treble back to neutral

19. Tune to a station on the FM1 Band and adjust Bass back to neutral

20. Listen to the AM station on preset 3 and adjust Bass back to neutral

21. Tune to a station on the FM1 Band and switch off the radio

BAND /PRESET 2 /TREBLE I LARGE KNOB 4--

BAND /SEARCH /BASS /LARGE KNOB 4--

BAND /PRESET 3 /BASS I LARGE KNOB 4--

BAND /SEARCH /BALANCE I LARGE KNOB -0-

BAND /PRESET l /BALANCE I LARGE KNOB -0-

BAND /SEARCH /TREBLE /LARGE KNOB -a-

BAND /PRESET 2 /TREBLE I LARGE KNOB -a-

BAND /SEARCH /BASS /LARGE KNOB -0-

BAND /PRESET 3 /BASS /LARGE KNOB -0-

BAND /SEARCH /OFF

'Table 7 .-5: Control tasks that had to be performed on the FM and AM Band ( left column). The right column contains the correct functions that had to be used.

59

Control task

Switch on the radio and tune to a station on the FMl Band.

Listen to the AM station on preset 4 and push the Loudness button.

Tune to a station on the FMl Band and adjust Balance back to neutral.

Abbreviated representation

ON FM 1 STATION

AM PRESET 4 LOUDNESS

FM 1 BALANCE NEUTRAL

Ta.ble 7.6: The left column contains some examples of control tasks that had to be performed by the subjecte. The right column contains the a.bbreviated form in which the control tasks were presented to the subjecte on the computer screen.

7.5 The radio single task condition

Directly following the training, the subjecte performed the control tasks on the radio in the Radio Single Task condition (RST). There was no secondary task they had to attend to. The subjecte only concentrated on the performance of the control tasks. The goal of the Radio Single Task condition (RST) was to obtain time measures from the performance of the control tasks while no other tasks had to be performed.

As in EXPERIMENT I, the cassette receiver was mounted in an adjusta.ble frame, at knee level, under a table. The subjecte were seated behind the table, on the left side of the cassette receiver. The control tasks were presented to the subjecte on a computer screen as follows:

l) The experimenter instigated the presentation of each control task by oparating a button that was connected with the computer.

2) After reading the control task, the subjects had to move their (right) arm to the right, in order to perform the control task on the cassette ~receiver. As the subject moved the right arm over a fixed point to perform the control task, the experimenter operated another button, electronically connected with the Metal selecter switch of the cassette receiver. The oparation of this button resulted in the recording of a "Metal" code in the remote computer. This "Metal" code indicated that the subject started the performance of the control taak (onset).

3) Shortly following this "Metal" code, the remote computer recorded the eperation of the functions that were used by the subject.

4) Directly following the final function, used by the subject, the experimenter operated the Metal button again. This way the offset of the control task was marked.

Table 7.7 contains an example of control task 3 in Table 7.4. The left column contains the time recordinga (hours: minutes: seconde: milliseconde), the middle column contains the recordinga of the used functions and the right

60

column contains a short explanation regarding the status of the cassette receiver. The onset as well as the end of the control task is indicated by the recording of a "Metal" code (see middle column).

Time Function Explanation

01.16:51:900 Metal ~of the control task 01.16:52:235 Band The Band knob is used ( from AM to LW) 01.16:52:750 Band The Band knob is used again (from LW to FM1) 01.16:54:300 S+ Th a Search button is used (upward direction) 01.16:55:135 ++ The volume level is changed (increased) 01.16:56:500 The volume level is changed (decreased) 01.16~ 57:400 Met al Qffset of the control task

Table 7.7: Example of a remote computer racerding in which a subject tunes te a FM1 station (starting on the AM Band) and changes the volume level.

In the Radio Single Task condition, all subjecte performed the control tasks (FM, AM, [FM/AM]l and [FM/AM]2) once and without a pause.

7.6 The reaction time single task condition

Following the Radio Single Task condition (RST), subjecte were assigned to the Reaction Time Single Task (RTST) condition. The goal of this condition was te obtain reaction time measures of the subjecte while they focuseed their attention only to the reaction time stimuli that were presented on a computer screen (Fig. 7.2). In the center of the computer screen, one out of two target stimuli appeared in random order for 0.5 seconde. This target stimulus was followed by one out of three response stimuli, randomly presented in one of the four corners of the screen.

Target stimuli y u

y Response stimuli u

V

Fig. 7.2: The target and response letter stimuli.

Figures 7.3 and 7.4 illustrate how the target stimulus and response stimulus was presented on the screen of a Macintosh computer.

In case the response stimulus was equal to the target stimulus the subjecte were expected to react by hitting a "yes"-button as quickly as possible. In case the response stimulus was not equal to the target stimulus the subjecte had to react by hitting a "no"-button as quickly as possible. The response buttons were placed on the left-hand side, in front of the subjecte. The subjecte, therefore, had to use their left hand to operate the response buttons.

61

r ""'\,

'Jl

' _;

I

Fig. 7. 3: Presentation of the target stimulus.

Fig. 7. 4: Presentation of the response stimulus.

In this condition, the right hand of the subjecte rested in front of them, on the surface of the table. The presented combinations of target and response stimuli are summed in Table 7.8.

Target stimulus

y y y u u u

Table 7.8:

Response Correct reaction stimulus

y yes u no V no u yes y no V no

The presented combinations of target and response stimuli.

It can be seen in Table 7. 8 that the number of "no re­sponses" is larger than that of the "yes responses". There­fore, the number of presented "target and response hits" (y­y, u-u) was made equal to that of the "target and response misses" (y-u, u-y, y-v, u-v). In other words, identical target and response stimuli were equally often presented as "not identical" target and

response stimuli. This way, the probability of occurrence of "yes-responses" was equal to that of the "no-responses". Each of the three response stimuli was equally often presented in either of the four corners of the screen. Therefore, the target responses had equal probability of occurrence in each of the four corners. This way, no response tendency would influence the results.

Each target stimulus, as well as each response stimulus was presented for 500 milliseconde. The interval between the presentation of the target stimuli and the response stimuli was either 1, 3 or 6 seconde. All three pause­durations ( 1, 3 or 6 seconde) had equal probability of occurrence. The subjecte had 2.5 seconde time to react to the response stimulus. Whenever a subject exceeded this response period, a sound was generated by the computer

62

to ~nform the subject that he either gave his reaction out of time, or had for~otten to react. Subsequently, 2 seconde after the subject reacted to a response stimulus or the response period had been exceeded (2.5 seconde), the next target stimulus was presented. The interval between the presentation of the response stimulus and the presentation of the next target stimulus is called the inter-trial interval. Table 7.9 depiets the five stages in each trial.

Stage

1. presentation of the target stimulus 2. interval 3. presentation of the response stimulus 4. response period 5. inter-trial interval

Duration

0.5 seconde 1, 3 or 6 seconde 0.5 seconde pause of 2.5 seconde 2 seconde

Table 7.9:The five stages that constituted each trial in the Reaction Time Single Taak condition.

7.7 The Radio Dual Task (RDT) condition

The third and final condition the subjecte were assigned to was the Radio Dual Task (RDT) condition. In the RDT condition the subjecte had to:

l) perferm thesetof control tasks on the radio (Table 7.2 - 7.5), 2) react (correctly and as quickly as possible) to the reaction time stimuli

presented on the computer screen.

The reaction time taak was, however, the subjecte• most important task. They were therefore asked to try to react correctly, and as quickly as possible to the reaction time stimuli that were presented on the computer screen. However, the control tasks also had to be performed correctly. As in the Reaction Time Single Taak condition, the subjecte operated the "yes" and "no" button with their left hand and used their right hand to operate the car radio. The subjecte focuseed their eyes on a computer screen on which the reaction time stimuli were presented. Following every 6th-9th target stimulus, a radio control task was presented to the subjecte on the computer screen for 3 seconds (see Table 7.10). The subjecte were expected to perferm the presented radio control task correctly. They a lso had to be alert for the response

.stimulus that would follow the control taak after a pause of either 1 or 3 seconde.

By presenting the control tasks visually instead of, for example audibly, the music coming from the cassette receiver did not interfere with the perception of the presented control tasks. Moreover, by presenting the control tasks on the ·computer screen, each of the subjecte received the control tasks in a standardized form, with the same duration and in the same order. Table 7.9 depiets the seven stages in each trial.

63

Staqe

1. presentation of a tarqet stimulus 2. pa u se 3. presentation of a control task 4. pause s. presentation of the response stimulus 6. response period 7. inter-trial interval

Dur at ion

0.5 seconde 1, 3 or 6 seconde 3 seconde 1 or 3 seconde 0.5 seconde 2.5 seconde 2 seconde

Table 7.10: The seven staqes that constituted each trial in the Radio Dual Task condition.

The dual task condition consisted of four sessions, each session containinq 85 trials. The total duration of one session was approximately ten minutes dependinÇJ on the reaction speed of the subjecte.

7.8 Subjects

The six subjecte (three male and three female) ranqed in aqe from 23 to 34 years. All subjecte were right handed. The subjecte were paid for their cooperation in the current experiment which lasted about 3 hours. Three of the subjecte in this experiment had cooperated in EXPERIMENT I as well.

It is not impossible that the subjecte who cooperated in the former experiment (EXPERIMENT I) as well, had an advantaqe in learninq or performinq the various radio control tasks. This miqht be a problem if, in the current experiment, each condition was formed by different qroups of subjecte. In such a situation, the qroup containing the more experienced subjecte would be favoured above others regarding their performance. Since, in the current experiment, each subject was exposed to all three experimental conditions (repeated measures design) a possible advantage due to prior learninq of these subjecte has, theoretically, been minimized. Therefore, the time measures of the more experienced subjecte were not compared with those of the less experienced subjecte.

7.9 Material

In the current experiment the same Philips cassette receiver was used as in EXPERIMENT I. This also holde for the remote computer that was used. The computer that was used for the presentation of the RTST stimuli, time measurement in the RST condition, and the presentation of the control tasks in the RST and RDT condition was a Macintosh MacPlus computer. For the creation and the presentation of the stimuli Psychlab (TM) was used, a computer proqram desiqned for creatinÇJ reaction time experiments.

64

a. Results and Discussion

8.1 General

In thie chapter, the focus will be on two different eorts of data namely:

1) The reaction time measuree that were obtained in the Reaction Time Single Taek condition as well as the reaction time measures that were obtained in the Radio Dual Task condition. In both conditione, subjecte responded to a number of reaction stimuli that were presented on the computer screen.

2) The time meaeures of the radio control tasks in the Radio Single Taek condition as well as the time measures of the radio control tasks in the Radio Dual Taek condition. In both conditions, subjecte performed a number of control tasks on the car radio.

Section 8.1 will focus on the first kind of time measurements. The rest of this chapter (section 8.2 and further) will focus on the time measures of the radio control tasks.

8.2 The reaction time measures

The subjecte responded to reaction time stimuli in the Reaction Time Single Task condition as wel! as in the Radio Dual task condition. In the Radio Dual Task condition, the subjecte were asked to perform the radio control tasks as their secondary task (i.e., the Reaction Time Taskwastheir most important task). This means that each subject should try to perform equally well on the reaction time tasks in both experimental conditions. If the subjecte succeeded in treating the Reaction Time Task as their most important task, the reaction time measures in the Reaction Time Single Task condition should not differ significantly from those in the Radio Dual task condition. However, if the subjecte focuseed part of their attention on the performance of the radio control tasks, a significant difference between the reaction time measures in the Reaction Time Single Task condition and those in the Radio Dual task condition is to be expected.

The right column of Table 8.1 contains the average Mediane (reaction times in milliseconde) of the Reaction Time Single Task condition and the Radio Dual Task condition. The Radio Dual Task condition consisted of four series of radio control tasks namely: control tasks on the FM Band, The AM Band and two series of control tasks on the FM as well as the AM Band. From now on these series will be referred to as task series (FM task series, AM task series, [FM/AM]l task series, and [FM/AM]2 task series).

Condition Average Median

Reaction Time Single Task (RTST) 978.0

Radio Dual Task (RDT) FM task series 1017.0 AM task series 956.0 [FM/AM}l task series 982.0 [FM/AM]2 task series 986.0

Table 8.1: Average mediane in milliseconde of the Reaction Time Task in the RTST condition and in the four task series of the RDT condition.

65

At first sight, the average Medians in both conditions hardly differ from each other. In order to check if the subjecte actually succeeded to perferm the Reaction Time Task as their most important task, the average Mediane of the Reaction Time Single Task cond.i.tien will be compared with those in the Radio Dual Task condition by means of an analysis of varianee (ANOVA). As stated earlier, it is expected that the reaction time measures in both conditions do not differ significantly from each other.

Table 8.2 contains the results of the ANOVA. The final column (p) indicates the level of significance. A significanee level of 0.05 or lower would indicate a significant difference between the time measures in both experimental conditions. The level of significanee in this ANOVA is 0.5797. Thus, the reaction time measures in the Radio Dual Task condition do not differ significantly from those in the Reaction Time Single Task condition.

Souree of df sum of Mean F p variatien squares square

Subjecte 5 179012.167 35802.433 Tasks 4 11392.633 2848.158 .734 .5797 Error 20 77636.667 3881.833

Table 8.2: ANOVA of the Reaction Times in the Reaction Time Single Task Condition and the Radio Dual Task condition.

From the results of this ANOVA we can conclude that the subjecte responded equally well to the reaction time stimuli in the reaction time single task condition and the radio dual task condition. If the subjecte in the radio dual task condition had focuaaed their attention more on the radio control tasks than on the reaction time stimuli, the reaction time measures would probably be significantly higher in the Radio Dual Task condition than these in the Reaction Time Single Taak condition. This finding is quite important. There are no significant differences found between the time meaaures of the Reaction Time Task in both experimental conditions. Therefore, it is possible that the performance of the radio control tasks in the Radio Dual Task condition is significantly slowed down by the fact that the subjecte treated the Reaction Time Task as their first and most important task. In sectien 8.2 the results of the Radio Single and Radio Dual Task condition will be compared with each other.

8.3 The results of the Radio Single Task and Radio Dual Task condition

This sectien will focus on the time measures of the radio control tasks in the Radio Single Task as well as in the Radio Dual Taak condition.

8.3.1 The Medians of the control tasks in the Radio Single Task and Radio Dual Task condition

Based on the results of the ANOVA in sectien 8.1 it is expected here, that the time needed to perferm the radio control tasks in the Radio Single Task condition will be shorter than in the Radio Dual Task condition. For all radio control tasks in the RST and ROT condition the Median has been calculated.

66

Table 8.3 contains the Mediane of all subjecte per experimental condition. At first glance, the time needed to perferm the radio control tasks in the Radio Single Task condition (RST) is indeed shorter than in the Radio Dual Task condition (RDT).

RST RDT

Mean 3.5 sec. 6.7 sec.

Table 8.3: Average medians of the RST and RDT condition.

Table 8.4, as well as Fig. 8.1 gives a more detailed overview of the time (Mediane), needed to perform the radio control tasks in all four task series in the Radio Single Task (RST) condition anci the Radio Dual Task (RDT) condit ion.

COntrol Tasks Condition RST RDT MEAN

FM 2.8 4.1 3.5 AM 2.1 3.6 2.9 [FM/AM]1 3.7 7.4 5.6 [FM/AM]2 5.2 11.7 8.5

MEAN 3.5 6.7

Table 8.4: Average.medians of the four task series in seconde in both experimental c~nditions.

In order to determine whether the differences regarding the time, needed to perform the radio control tasks in both conditions are significant, an Analysis of Varianee (ANOVA) was computed. Table 8.5 contains the summary of the results of this ANOVA.

Souree of df Sum of Mean F p variatien squares square

Subjecte 5 51.247 10.249 condition 1 127.694 127.694 22.231 .0053 Error 5 28.720 5.744 Task series 3 234.149 78.050 36.317 .0000 Error 15 32.237 2.149 Interaction 3 53.002 17.667 6.456 .0051 Error 15 41.051 2.737

Table 8.5: ANOVA summary table for all four Task Series.

67

The final column in Table 8.5 (p) indicates that there are three significant effects.

1) The first significant effect is that of the experimental conditions (p=0.0053). The overall mean in the Radio Dual Task condition (Table 8.4) is significantly higher than in the Radio Single Task condition.

2) The second significant effect is that of the task series (p= 0.0000). The task series contributed differentially to the overall effect.

3) The third significant effect is an interaction effect. This means that one (or more) of the task series (FM, AM, [FM/AM]l, (FM/AM]2) was affected more in one of the experimental conditions than the other task series.

In order to specify which of the task series (FM, AM, [FM/AM]l, [FM/AM]2) contributed to the interaction effect, a Tukey post hoc comparison was computed. The results of this comparison are given in Table 8.6. The upper triangle indicates significant differences at 0.05 level, the lower triangle indicates significant differences at 0.01 level.

A. B. c. D. E. F. G. H.

A. AM (RST) x si s B. FM (RST) x s s c. AM (RDT) x s si D. [FM/AM]l (RST) - x s s E. FM (RDT) x si F. [FM/AM]2 (RST) - x s G. [FM/AM]l (RDT) s s x si H. [FM/AM]2 (RDT) s s sii s sii s sii x

Table 8.6: Summary table of the T~key post hoc comparison (upper t~~angle: 0.05 level ( 1

), lower triangle: 0.01 level (11) ).

The Tukey post hoc comparison reveals an interesting result. The [FM/AM]2 (RDT) task series differs significantly w.ith the FM (RDT), AM .(RDT) and [FM/AM]l (RDT) task series at 0.05 level ( 1

) as well as at 0.01 ( 11) level.

Apparently, the [FM/AM]2 task series were more affected in the Dual Task condition as compared with the FM, AM and [FM/AM]l task series. This finding is illustrated in Fig. 8.1. It can be seen that the [FM/AM]l and [FM/AM]2 task series are relatively more affected in the Dual Task condition than the FM and AM task series. The [FM/AMJ2 tasks series, however, is more affected in the Dual Task condition than the [FM/AM}l task series. This finding is illustrated by the significant interaction effect (Tables 8.5 and 8.6).

68

Average Medians of the four Task Series

13

12 11 7

11

10

~ 9 0 V Ql (I) 8 c ·-@

7

«l

'0 6

~ Ql

5 0'1 «l

liJ 4

> < 3

2

1

0 Single Task condition Oual Task condition

f2:Zl FM !SSJ AM fZ::Zj FM/AM1 ~ FM/AM2

Fig. 8.1: Average mediane of the four task series in both experimental eonditions.

8.4 Task-parts

Although the Taak Series consist of various differing radio eontrol tasks, a number of them do share similar operatien steps. For instance: control task number 5 of the FM task series contains two operatien steps that are similar to the control task number 5 of the AM task series namely:

FM control task 5: STATION > BASS > LARGE KNOB (4--)

AM control task 5: PRESET > BASS > LARGE KNOB (4--)

The two final eperation steps (BASS > LARGE KNOB) are present in both control tasks. Although the original control tasks are not identical it is possible to divide them up into smaller and therefore identical parts namely:

BASS > LARGE KNOB (4--)

From now on, the smaller parts that make up the control tasks will be referred to as so-called task-parts. A task-part always consiste of two or more operatien steps.

69

Thus, by dividing the control tasks into smaller task-parts it is possible to perform a detailed post hoc analysis regarding the operatien time of the various operatien steps. This means that the time analysis is not limited anymore to that of identical control tasks, but is also possible regarding the various similar eperation steps and operatien sequences, that constituted the various control tasks in the four taak series. This way, the average time needed to perferm the various operatien steps can be calculated more accurately since the total number of observations is increased.

8.5 Task-part analyses

This section will contain the results of a number of task-part analyses. In the task-part analyses, the differences that may exist regarding the performance of a number of operatien steps in both experimental conditions will be analyzed. The task-parts in the Single and Dual task conditions that will be analyzed are summed in Table 8.7. The first four task-parts contain two operatien steps. The fifth and sixth task-part contain three eperation steps. The final two task-parts contain four eperation steps.

The Preset>Loudness sequence will be analyzed in section 8.6.1 and will be referred to as the P-Loud task-part.

The Autostore>Preset sequence will be analyzed in sectien 8.6.2 and will be referred to as the Ast-P task-part.

The Sound Functions>Large knob (4--) sequence will be analyzed in section 8.6.3 and will be referred to as the S.Functions-Large knOb 4-- taak-part.

The Sound Functions>Large knob (-0-) sequence will be analyzed in section 8.6.4 and will be referred to as the S.functions-Large knOb -0- task-part.

The Preset>Sound Functions>Large knob (4--) sequence will be analyzed in section 8.6.5 and will be referred to as the P-S.fynctions-Large knOb 4-­task-part.

The Preset>Sound Functions>Large knob (-0-} sequence will be analyzed in sectien 8.6.6 and will be referred to as the P-S.FUnctions-Large knOb -a­taak-part.

The Band>Preset>Sound Functions>Large knob (4--) sequence will be analyzed insection 8.6.7 and will be referred to as the Band-P-S.Functions-Large knOb 4-- task-part.

The Band>Preset>Sound Functions>Large knob (-0-) sequence will be analyzed in section 8.6.8 and will be referred to as the Band-P-S.Functions-Large knob -o- taak-part.

70

r---·

Task-parts Number of steps

Preset > Loudness 2

Autostore > Preset 2

Sound Functions > Large knob (4--) 2 Sound Functions > Large knob (-0-) 2

Preset > Sound Functions > Large knob (4--) 3 Preset > Sound Functions >Large knob (-0-) 3

Band > Preset > Sound Functions > Large knob (4--) 4 Band > Preset > Sound Functions > Large knob (-0-) 4

Table 8.7: The left column contains the task-parts that will be analyzed in this section. The right column contains the number of operatien steps of the task-part involved.

8.5.1 Remote box recording problems, due to varying search times of Automatic Tuning

During the experiment it was noted that the time the radio needed to tune to stations was varying from moment to moment. Once a station was found by using Automatic Tuning and the function was used again in order to tune to another station, the search time was either shorter or langer. It even happened repeatedly that subjecte operated Automatic Tuning and shortly after it, while the radio was still busy searching for the next station, operated a next function button (e.g. Base). As a result, the internal processor of the radio

·· did notpiek up the operatien of the Baas button. Consequently, the remote box was not able to make proper time recordinga of the button eperation during the search process of Automatic Tuning. Due to this system characteristic, no task-part analysis is performed of the tasks containing Automatic Tuning. The differences in search time are considered to be an uncontrolled factor in this experiment.

8.5.2 Assumptions regarding the operatien of the sound function and the preset function

It is assumed here that the operatien of the Treble, the Base and the Balance -buttons do not differ substantially from each other, regarding their ease of use. Put another way, the time needed to reach for and operate each of the sound function buttons is aseumed to be the same. The same assumption is held for the operatien of the five Preset buttons. The sound function buttons, as well as the Preset buttons are physically grouped tagether at the front of the car radio. Differences intheir so called "access time" (i.e., time needed to reach for and operate a button) of the Sound function buttons and the Preset buttons will be marginal. Moreover, the possible differences in access time of bath functions at micro level are beyend the scope of this experiment. Since it is assumed that the ease of use of these sound functions is equal, the various sound functions (Treble, Bass and Balance) will be treated as one and the same. Therefore, instead of computing the average time needed to operate the Baas button, the Treble button or the Balance button, all Sound function buttons are treated as one, namely a sound function. With regard to the preset buttons, the same procedure is followed.

71

8.6 The task-part analyses

8.6.1 Analysis ·of the task-part P-Loud

In the P-Loud task-part the subjecte operated a Preset button directly followed by the Loudness button. This sequence was performed once in the AM taak series and twice in the [FM/AM]l taak series by all six subjecte in the Radio Single Task condition as well as in the Radio Dual Taak condition. From these time measures the median was calculated. Finally, the mediane from all subjecte was averaged. The two right columns of Table 8.8 contain the average Mediane in both experimental conditions of the task-part P-Loud in the AM and {FM/AM]l taak series.

Task-part Taak series ST DT MEAN

P-Loud AM 1.0 1.4 1.2 [FM/AM]l 1.5 3.1 2.3

MEAN 1.3 2.3

Table 8.8: Average Mediane of the task-part P-Loud in the AM and [FM/AM]1 task series.

As can be seen in Table 8.8, the mediane of the P-Loud task-part in the AM and [FM/AM]l task series in the Dual Taak condition are higher than those in the Single Task condition. In order to see whether the differences between the mediane in the Single Task and Dual Task condition are significant, an Analysis of Varianee was computed. Table 8.9 contains a summary of the results of this ANOVA.

The level of significanee regarding the effect of the experimental condition is 0.1012. This means that there is no significant difference regarding the overall performance of the P-Loud task-part in the experimental conditions. The significant effect of the tasks parts (p • 0.0027) indicatea that there is a significant difference regarding the performance of the P-Loud taak­part in the FM task series and the performance of the P-Loud task-part in the [FM/AM]1 task series. The mean of the [FM/AM]1 taak-part in both experimental conditions (M=2.3) is significantly higher than the mean of the AM task-part in both experimental conditions (M=1.2).

Souree of df Sum of Mean F p variation squares square

Subjecte 5 13.099 2.620 Experimental condition 1 5.794 5.794 4.022 0.1012 Error 5 7.203 1.441 Task-parts 1 6.899 6.899 30.146 0.0027 Error 5 1.144 0.229 Interaction 1 2.067 2.067 2.936 0.1473 Error 5 3.519 0.704

Table 8.9: Anova summary table for the task-part P-Loud.

72

Task part P- Loud

3.5

3.1

3

UI '0 2.5 c 0 u Cll Ul

t: 2 -!':! «l

'0 1.5 ~ Ql en «l

àJ >

1 <(

0 5

0

Single Task condition Dual Task condition

!ZZJ AM l:s:SJ [ FM/ AM] 1

Fig. 8.2:Average mediane of the task part P-Loud in the AM and [FM/AM]1 Task series.

During the analysis of the remote box recordings, it became clear that the Loudness function was not recorded a number of times. Although the subjecte in these cases touched the loudness button in the task series, it then did not result in switching on or off the loudness function. Table 8.10 contains the number of these activation errors in the FM, AM and [FM/AM]1 and [FM/AM]2 task series in both experiméntal conditions.

Task Series ST OT

FM 0 3 AM 1 2 [FM/AM]1 0 2 [FM/AM]2 1 3

Table 8.10: Number of activation errors con­cerning the Loudness button in both experimental conditions.

73

8.6.2 Analysis of the task-part: Ast-P

In the Ast-P taak-part, the subjecte operated the Autostore button directly followed by a Preset button. Each subject performed the Autostore > Preset sequence three times (once in the AM taak series and twice in the [FM/AM]1 taak series) in the Single Taak condition as well as in the Dual Taak condition. The two right columns of Table 8.11 contain the average Mediane of the Ast-P task-part in both experimental conditions. The mediane of the FM and AM taak series in the Dual Task (DT) condition are somewhat higher than in the Single Taak (ST) condition. The median of the Ast-P task-part in the [FM/AM]1 taak series is doubled, however.

Task-part Task series ST DT MEAN

Ast-P FM 0.9 1.0 1.0 AM 0.9 1.1 1.0 [FM/AM]1 1.1 2.2 1.7

MEAN 1.0 1.4

Table 8.11: Average Mediane of the task-part Ast-P in the FM, AM and [FM/AM]1 task series.

In order to see whether the mediane in the Dual Task condition are significantly higher than in the Single Taak condition, an Analysis of Varianee was calculated. The results of this ANOVA, which are summed in Table 8.12, reveal significant effects regarding the experimental cond~tion

(p=0.0281) and the task-parts (p=0.0065).

Souree of df Sum of Mean F p variation squares square

Subjecte 5 5.446 1.089 Experimental condition 1 1.916 1.916 9.371 0.0281 Error 5 1.022 0.201 Task-parts 2 3.805 1.903 8.679 0.0065 Error 10 2.192 0.219 Interaction 2 1.629 0.815 2.466 0.1347 Error 10 3.304 0.330

Table 8.12: Anova summary table for the task-part Ast-P

The significant effect of the experimental condition shows, that the time needed to perform the Ast-P task-part is significantly higher in the Dual Taak condition (M=1.4) than in the Single Taak condition (M=1.0).

The significant effect of the task-parts means that the task-parts contributed differentially to the overall effects of the experimental conditions. In other words, the task-parts in the FM, AM, [FM/AM]1 and the [FM/AM]2 taak series were not equally affected by the Dual Taak condition. In order to aee which of the task-parts was affected significantly more by the Dual Task condition, a Tukey post hoc analysis was calculated. The results of this analysis are summed in Table 8.13.

74

According to the results of the Tukey post hoc comparison, the Ast-P task­part in the [FM/AM]l task series differs significantly with the Ast-P task­parts in the FM and AM task series. This means that the Dual Task condition had significantly more effect on the Ast-P task-part in the [FM/AM]l task series than in the FM and AM task series. This finding is also illustrated in Fig. 8.3. In this bar graph it can be seen that the average mediane of the Ast-P task-part in the FM task series as well as in the AM task series are raised marginally, whereas the Ast-P task-part in the [FM/AM]l task-part is raised substantially in the Dual Task condition.

A. B. c.

A. FM Task Series x si

B. AM Task Series x s c. [FM/AM]l Task Series sii x

Table 8.13: Summary table of the Tukey post hoc comparison (upper triangfe: 0.05 level ( 1

), lower triangle: 0.01 level ( 11 > ).

Task part Ast-P

2.6 .---------------------------------------------------------~

2.4

2.2 2.2

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

Single Task condition Dual Task condition

[22} FM [SSj AM ~ [FMIAMJ1

Fig. 8.3:Average mediane of the task part Ast-P in the FM, AM and [FM/AM]l task series.

75

8.6.3 Analysis of the task-part: s.Functions-Large knob 4--

In this taak-part, subjects operated and adjusted the sound functions Treble, Baas and Balance nine times; three times in the FM taak series, three times in the AM taak series and three times in the [FM/AM]l task series. All subject a were asked to turn the Large knob swiftly to the left, without looking at the display. In order to adjust the Treble level it is sufficient to listen to the changing Treble level. In other words, the level of the Sound functions can, in most cases, be adjusted by making use of the auditive feedback, i.e. the change in the color or direction of the sound. Thus, while driving a car it is not necessary to look at the display of the car radio. In this task-part, the subjecte adjusted the sound functions without making use of the visual feedback from the display. The adjuetment was made by making u se of auditive feedback, so the setting 4-- was only approximated.

As stated earlier, the Baas, Treble and Balance button operations are assumed not to differ concerning their ease of use. Therefore, the Base, Treble and Balance functions are treated as if they were the same, e.g. as sound functions. Table 8.14 contains the average Mediane of the operatien of the task-part Sound functiena-Large knob 4-- per taak series in both experimental conditions.

Task-part Taak series ST DT MEAN

S.Functions-Large knob 4-- FM 0.9 1.0 1.0 AM 0.8 1.4 1.1 [FM/AM]l 0.9 1.6 1.3

MEAN 0.9 1.3 .

Table 8.14:Average Mediane for the task-part S.Functions-Large knob 4-- in the FM, AM and [FM/AM]1 taak series.

An Analysis of Varianee was computed to see what the effects of the experimental condition and the task-parts were concerning the ease of use of the adjustment of the Sound functions. Table 8.15 contains the results of this ANOVA.

Souree of df Sum of Mean F p ~

variatien squares square

Subject a 5 .235 .047 Condition 1 2.103 2.103 29.462 .0029 Error 5 .357 .071 Task-parts 2 .501 .250 1.882 .2024 Error 10 1.330 .133 Interaction 2 .672 .336 2.071 .1768 Error 10 1.623 .162

Table 8.15: Anova summary table for the task-part S.Functions-Large knob 4--.

The only significant effect is that of the experimental condition (p = 0.0029). This means that the overall mean in the Dual Taak condition (M=1.3)

76

is significantly higher than in the Single Task condition (M=0.9). Fig. 8.4 contains a bar graph with the average medians of the task-part s.Functions-Large knob 4-- in all three task series. Although the average median is raised most in the [FM/AM]l task series, the difference with the remaining two taak series is not significant.

Task part: S.Functions Large knob 4--

2 1.9

1.8

1.7 1.6

1.6

UI 1.5 g 1.4 0

á:: 1.3 (J)

t: 1.2

1.1 ~ 1 tO

~ a 9

0.8

~ 0.7 tO 1.. 0.6 ~ >

0.5 <t

0.4

0.3

0.2

0.1

0

Single Task condition Dual Task condition

l22l FM [SSJ AM !?LZ1 (FM/AM] 1

Fig. 8.4:Average mediane of the task part S.Functions-Large knob 4-- in the FM, AM and [FM/AM]l task series.

77

8.6.4 Analysis of the task-part: s.Functions-Large knob -o-

In this taak-part, subjecte operated and adjusted the sound functions Treble, Baas and Balance nine times7 three times in the FM taak series, three times in the AM taak series and three times in the [FM/AM]2 taak series. The subjecte were asked to adjust the sound functions back to neutral. In order to do so, visual feedback from the display of the car radio was essential. The sound functions ware properly adjusted back to neutral if the display showed (-0-). The goal of this task-part was to investigate how easy it is to adjust the sound functions back to neutral.

Table 8.16 contains the average Mediane of the task-parts in which the Sound functions ware adjusted back to neutral (-0-).

Task-part Task series ST DT MEAN

S.Functions-Large knob -o- FM 1.9 4.5 3.2 AM 2.5 4.2 3.4 [FM/AM]2 1.9 4.9 3.4

MEAN 2.1 4.5

Tabla 8.16: Average Mediane for the task-part S.Functions-Large knob -o-

It can be seen in Table 8.16 that the average mediane in the Dual Taak condition are substantially raised. In order to see whether the differences between the Single and Dual task condition are significant, an Analysis of Varianee was computed. Table 8.17 contains the results of this ANOVA. As in the former task-part analysis, only the effect of the experimental condition is significant (p=0.0124). This means that the overall mean in the Dual Taak condition (M=4.5) is significantly higher than in the Single Taak condition (M=2.1).

Souree of df Sum of Mean F p variation squares square

Subjecte 5 20.892 4.178 Condition 1 53.641 53.641 14.568 .0124 Error 5 18.410 3.682 Task-parts 2 .244 .122 .132 .8775 Error 10 9.198 .920 Interaction 2 2.898 1.449 1.035 .3903 Error 10 13.996 1.400

Tabla 8.17: Anova summary table for the task-part S.Functions-Large knob -o-

Fig. 8.5 contains a bar graph containing the average mediane of the task­part s.Functions-Large knob -o- in the FM, AM and [FM/AM]2 taak series. The median in the (FM/AM]2 taak series is the highest one.

78

Task part S.Functions Large knob -0-

6 ,----------------------------------------------------------;

5 4.9

Ë 0 4 u ~ m c -m c 3 ~

0

~ ~ 0 2 ~

~ > ~

1

Single Task condition Dual Task condition

~ AM ~ [FM/AM]2

Fig. 8.5:Average Mediane of the task part S.Functions-Large knob -0- in the FM, AM and [FM/AM]2 task series.

79

8.6.5 Analysis of the task-part: P-S.FUnctions-Large knob 4--

In this task-part, subjecte operated a preset button and adjusted the sound functions Treble, Bass and Balance six times; three times in the AM task series and three times in the [FM/AM)1 task series. Table 8.18 contains the average Mediane of the operatien of the task-part P-Sound functions-Large knob 4-- per task series in both experimental conditions.

Task-part Task series ST DT MEAN

P-S.Functions-Large knob 4-- AM 2.5 3.5 3.0 [FM/AM]1 2.4 5.0 3.7

MEAN 2.5 4.3

Table 8.18: Average Mediane of the task-part P-S.Functions-Large knob 4--

It can be seen that the overall mean in the Dual Task condition (M=4.3) is higher than in the Single Task condition (M=2.5). In order to see whether this difference is significant an Analysis of Varianee was computed. Table 8.19 contains the results of this ANOVA.

Souree of df Sum of Mean p variatien squares square

Subjecte 5 5.483 1.097 eondition 1 19.874 19.874 38.580 0.0016 Error 5 2.576 0.515 Task 1 3.103 3.103 3.328 0.1277 Error 5 4.662 0.932 Interaction 1 3.219 3.219 3.751 0.1105 Error 5 4.291 0.858

Table 8.19: Anova summary table of the task-part P-S.Functions-Large knob 4--

Table 8.19 reveals that the only significant effect is that of the experimen­tal~condition (p = 0.0016). In other words, the overall mean in the Dual Task condition (M=4.3) is significantly higher than in the Single Task condition (M=2.5).

Fig. 8.6 contains a bar graph of the average mediane of the current task­part in the AM and (FM/AM]l taak series. As in all fermer task-part analyses, the average median of the task-part in the [FM/AM]l task series is highest as compared with the task-parts in the FM and AM task series.

80

Task part: P-S.Functions-Large knob 4--

6 ,-------------------------------------------------------~

5.0 5

4

(J)

~ 3

2

1

Single Task condition Dual Task condition

IZ2J AM !SSJ [FM! AM] 1

Fig. 8.6:Average medians of the task part P-S.Functions-Large knob 4-- in the AM and [FM/AM]l task series.

81

8.6.6 Analysis of the task-part: P-S.Functions-Large knob -o-

Table 8.20 contains the average Mediane of the P-S.Functions-Large knob -o­task-part. In this task-part, a Preset button, a sound function button and the large knob was operated. Subjecte were asked to adjust the sound functions back to neutral.

Task-part Task series ST DT MEAN

Preset-S.Functions-Large knob -o- AM 3.7 6.3 s.o [FM/AM)2 3.3 8.7 6.0

MEAN 3.5 7.5

Table 8.20: Average Mediane for the task-part P-S.Functions-Large knob -0-

The overall mean in the Dual Task condition is doubled, compared to the Single Task condition. In order to see whether this increase is significant, an Analysis of Varianee was computed. The results of this ANOVA are summed in Table 8.21.

Souree of df Sum of Mean F p variatien squares square

Subjecte 5 33.658 6.732 Condition 1 94.784 94.784 13.568 0.0142 Error 5 34.929 6.986 Taak 1 6.186 6.186 1.188 0.3254 Error 5 26.029 5.206 Interaction 1 11.655 11.655 1.906 0.2259 Error 5 30.57 6.114

Tabla 8.21: Anova summary table for the task-part P-S.Functions-Large knob -o-

The only significant effect is that of the experimental condition (p • 0.0142). The increase of the overall mean in the Dual Taak condition is thus significant.

Fig. 8.7 contains a bargraphof the task-part P-S.Functions-Large knob -a­in the AM and [FM/AM]2 taak series. The increase of the performance time is

highest in the [FM/AM)2 task series.

82

Task par-t P-S.Functions-Lar-ge knob -0-10

9 8.7

8

E 7 0 V Cl) 111

6 c: -111 c 5 10

~ 4 Cl) OI ltl

iv 3

~ 2

1

0 Single Task condition Dual Task condition

IZZJ AM !SSJ [ FM/ AM] 2

Fig. 8.7:Averaqe medians of the task part P-S.Functions-Larqe knob -0- in the AM and [FM/AM]2 task series.

83

8.6.7 Analysis of the task-part: Band-P-S.Functions-Large knob 4--

Table 8.22 contains the average Mediane of the task-part Band-P-S.Punctions­Large knob 4--. In this task-part, subjecte operated the Band button, a Preset button and adjusted the Sound functions with the large knob. The subjecte performed this task-part three times in the [FM/AM]l task series.

Task-part Task series ST DT MEAN

Band-Preset-s.Functions- (FM/AM]l 4.4 8.8 - 6.6 Large knob 4--

Mean 4.4 8.8

Table 8.22: Average Mediane for the task-part Band-P-S.Functions-Large knob 4--

The overall mean in the Dual task condition is doubled, as compared with the Single task condition. An Analysis of Varianee was computed to see whether this increase was significant. The results of this ANOVA are summed in Table 8.23.

Souree of df Sum of Mean F p variatien squares square

Subjecte 5 20.316 4.063 COndition 1 59.363 59.363 9.870 0.0256 Error 5 30.072 6.014

Table 8.23: Anova summary table for the task-part Band-P-S.Functions-Large knob 4--

The significanee level of 0.0256 in the final column of Table 8.23 indicates that the increase of the overall mean in the Dual Task condition is indeed significant. Fig. 8.8 contains a bar graph of the task-part Band-P­S.Functions-Large kriob 4--.

84

Task part Band-P-S.Funct-L.knob 4--10

9 8.8

8

(J)

g 7 0 á! (J)

c:: 6 -(J) c:: 5 11:1

'0

~ <4 Q) 0> 11:1

bi 3 > <

2

1

0 Single Task condition Oual Task condition

IZ:ZJ [ FM/ AMJ 1

Fig. 8.8:Average medians of the Taak part Band-Preaet-S.Functiona-Large knob 4-- in the [FM/AM]l taak series.

85

8.6.8 Analysis of the task-part: Band-P-S.Functions-Large knob -o-

Table 8.24 contains the average Mediane of the task-part Band-P-S.Functiena­Large knob -0-. In this task-part, subjecte operated the Band button, a Preset button and adjusted the Sound functions back to neutral with the large knob. The subjecte performed this task-part three times in the [FM/AM]2 task series.

Task-part Task series I ST DT MEAN

Band-Preset-S.Functions- [FM/AM]2 5.6 11.5 8.6 Large knob -o-

Mean 5.6 11.5

Table 8.24: Average Medians for the task-part Band-P-S.Functions-Large knob -o-

As in the farmer task-part, the overall mean is doubled in the Dual Task condition. The results of the Analysis of Varianee that was computed are summed in Table 8.25.

Souree of df Sum of Mean F p variatien squares square

Subjects 5 48.607 9.721 condition 1 105.045 105.045 15.276 0.0113 Error 5 34.383 6.877

Table 8.25: Anova summary table for the task-part Band-P-S.Functions-Large knob -o-

The final column in Table 8.25 indicates a significant effect of the experimental condition (p=0.0113). In ether words, the increase of the overall mean is significant. Fig. 8.9 contains a bar graph of the task-part Band-P­S.Functions-Large knob -o-.

86

Task par-t Band-P-S.Funct-L.knob -0-13

12 11.5

11

10 (IJ

'E 9 0 ~ !11 8 c -~

7

«<

~ 6

5 ()) OI «<

4 ài ~

3

2

1

0 Single Task condition Dual Task conaltion

IZZl [FM/ AM] 2

Fig. 8.9:Average medians of the Task Part Band-P-S.Functions-Large knob--0-in the FM/AM task series.

87

8.7 Unexpected system characteristics of the oe 685 car radio

8.7.1 Differential search time of the function Automatic Tuning

In the radio control tasks in the FM Task series, subjecte frequently had to use the Automatic tuning function. In a number of cases, the subjecte experienced difficulties during the oparation of it (see also section 8.4.1.). The subjecte performed the various radio control tasks quite rapidly. A sequence of three oparation steps was, on the average, performed relatively fast. But, whenever the subjecte attempted to operate a function, directly following Automatic tuning they, now and then, experienced difficulties. After pressing the Automatic tuning button, the radio started a search process, in order to find a (new) station. The amount of time, needed to find a new station, differed substantially from station to station. In a number of cases the new station was quickly found. However, in a number of other cases the search time was quite long. Consequently, the internal processor of the car radio did not piek up a button oparation attempted during such long search times.

Duè to these differentlal search times, subjecte therefore experienced great difficulties in performing oparation sequences following Automatic Tuning. Whenever, for instance, Bass had to be adjusted, directly following the oparation of Automatic Tuning, the internal processor of the radio did not piek up the subsequent oparation of the Bass button. As a result, the processor only picked up the oparation of the Large knob and the volume level was, thus, increased or decreaeed unexpectedly. Proper (re)adjustment of the Bass level took quite some time after such an unexpected interrupt.

This system characteristic: a differentlal search time of Automatic tuning, was not anticipated, prior to the experiment. Therefore, all radio control tasks containing Automatic Tuning were not analyzed, for two reasons:

1) During the analysis of these events, the Remote box recordinga proved to be invalid. In a substantial number of cases the button operation, immediately following Automatic tuning, was not recorded since the processor was still busy tuning to another station. As a result, it was not pousible to deduce whether the delay in the performance of the radio control taak was either an effect of this system characteristic or an effect of the Dual Task condition.

2} The inferences, drawn from the time measures of these radio control tasks would be confounded due to the differentlal search times of the Automatic tuning function.

8.7.2 Difficulties in the Autostore operation mode

Another characteristic of the DC 685 that was not anticipated is related to the effect of the operatien of the Band button in the Autostore oparation mode. During the experiment it became clear that subjecte were able to switch from the AM band to the FM band quite easily. In order to do so, the subjecte had to push the Band button more than once. If they started the radio control taak on the AM Band, they had to push the Band button twice. After pushing it once, they changed the wave range from AM to LW, and after pushing the Band button twice they reached the FM! band. In order to change from the FMl to the

88

AM band, aubjects had to push the Band button twice again. The aequence then was: from FMl to FM2 and from FM2 to the AM Band. After having performed a number of radio control taska containing the eperation of the Band button, subjects knew by heart how many times they had to push the Band button to switch from the AM to the FM band or vice versa.

Bowever, if subjecte had to switch to another wave range in the Autostore operatien mode, problems arose. When in the Autostore eperation mode, the Band button had to be operated one extra time. The first time the subjecte operated the Band button caused the radio to switch from the Autostore eperation mode back to the normal eperation mode. once the radio was in the normal operatien mode, the Band button had to be operated the uaual number of times. Although the subjecte were trained with regard to this system characteristic, problems arose, aince they did not know by heart in what mode the radio was all the time. Repeatedly, subjects therefore operated the Band button incorrectly while the radio was in the Autostore operatien mode. Once they noticed their error, either by themselves or helped by the experimenter, they began the operatien of the Band button from the start.

The analysis of the radio control tasks in which these errors were made was, however, still possible. By the time the subject reached the proper Band wave, the performance of the rest of the radio control task could be continued.

Table 8.26 contains a summary of these Band wave errors in the [FM/AM)l and [FM/AM}2 taak series. Bere a Band wave error is defined as: the number of occasions in which the subjects pressed the Band button either too often or not often enough. For instance: if a subject fails to select the FMl Band, he or she makes a Band Wave error. No matter how many times the subject has to press the Band button in order to reach the proper Band wave, such a failure is defined as one Band wave error.

One subject had to operate the Band button 14 times in a row in order to select the proper wave range in·the Dual Taak condition. She had to operate the Band button three times in order to reach the AM Band (once, to leave the Autostore operatien mode, once to change from FMl to FM2 and once to change from FM2 to AM). However, she kept on pushing the Band button twice in stead of three times. As a result, she did not succeed in reaching the AM Band. It was not until her last trial that she discovered she had to push the Band button only one extra time. Although she had to prees the Band button 14 times, she only made one Band wave error according to our counting system: she forgot to push the Band button one extra time at the onset of her trial.

The left column of Table 8.26 contains the number of errors in the Single Taak Condition: none. The right column contains the Band wave errors that were made in the Dual Taak condition. Only the [FM/AM] 1 and [FM/AM] 2 task-parts contained radio control tasks in which the Band button had to be operated.

Taak Series Condition ST OT

[FM/AM]l 0 5 [FM/AM]2 0 4

Table 8.26: Number of Band wave errors in both experimental conditions.

89

It should be noted that the total number of Band wave errors might be larger than denoted here. It is not possible to define exaetly on how many occasions subjecte preseed the Band button not often enough, but correeted their error by pushing the Band button again onee they became aware of their error. Therefore, the number of Band wave errors in Table 8.26 is an underestimation of the actual number of Band wave errors.

8.8 The performance of the radio control tasks

During the performance of the task series in the Radio Dual Task eondition, I some of the subjecte had diffieulties in remembering the visually presented radio eontrol tasks. For example, a radio eontrol task was presented briefly on the computer sereen. The subject started with the performanee of the radio eontrol task. During his or her performance, .a target stimulus was presented on the computer screen. Since the subjecte were told to reaet eorreetly and as quickly as possible to the reaetion time stimuli, the subject immediately concentrated on the computer screen in order to reaet to the response stimulus that was about to be presented. By the time the response stimulus was presented and reacted upon, the subject eontinued with the performance of the radio control task again. Now and then, subjecte indicated they had forgotten what the complete radio eontrol task was. Table 8.27 shows how often these problems arose in the Radio Dual Task eondition. If the subject indicated to have forgotten what the radio eontrol task was, the experimenter helped the subject by telling him or her what oparation steps still had to be performed.

Task series Experimental condition Subject RST RDT number

FM 0 2 3 AM 0 1 6 [FM/AM]l 0 2 2,4 [FM/AM]2 0 4 2,4,6

Table 8.27:Number of times subjecte indieated to have forgotten a part of the radio control task. The final column indieates how many different subjecte suffered diffi­eulties remembering a part of a radio eontrol task in the task series eoncerned.

The final column of table 8.27 shows whieh subjecte suffered-difficulties in remembering parts of the radio control task. It can be seen that one subject (subject nr. 3) suffered diffieulties on two occasions in the FM task series. Three subjecte suffered difficulties remembering parts of a radio eontrol task in the (FM/AM]2 task series on four occasions. In other words, one of these subjecte suffered diffieulties on two occasions. It is important to note hare, that the subjecte had no difficulties in performing the radio eontrol tasks. Although their performanee slowed down in the Radio Dual task eondition, they had no diffieulties in either finding or oparating the correct functions.

90

9. Conclusions

9.1 The performance of the Reaction Time task

As stated in section 8.1, there are no significant differences found between the time measures of the Reaction Time Task in the Reaction Time Single Task condition and the Radio Dual Task condition. In other words, the subjecte responded equally wel! to the reaction time stimuli in both conditions. There­fore, it is quite well possible that the performance of the radio control tasks in the Radio Dual Task condition is significantly slowed down due to the fact that the subjects treated the Reaction Time Task as their first and most important task. Bere, it is assumed that the subjects treated the Reaction Tiae Single Task indeed as their aost iaportant task. Therefore, the parallel that is mentioned in section 7.1 is assumed to be present: as in driving a car, the subjecte focuseed part of their attention on a visual task.

9.2 Performance of the Task-parts

The task-part P-Loud is the only task-part in which the Dual Task condition had no significant effect on the performance of the task-parts.It can thus be concluded that the subjecte operated the P-Loud task-part equally wel! in both experimental conditions. In the remaining task-parts, however, the subjecte performed the oparation sequences significantly slower in the Dual Task condition than in the Single Task condition. In other words, except for the task-part P-Loud, the increase of the mediane in the Dual Task condition was a significant increase.

9.2.1 The extent to which the Task-parts were affected by the Dual Task condition

Table 9.1 contains the means in seconde of the experimental conditions per task-part. The task-parts are sorted by the increase in the Ou al Task condition. As stated earlier, the increase of the P-Loud task-part is the only increase that was not significant.

Single Task Dual Task Increase

Sound F. Large Knob 4-- 0.9 sec. 1. 3 sec. 11 0. 4 sec.

Ast-P 1.0 sec. 1.4 sec. 0.4 sec.

P-Loud 1.3 sec. 2.3 sec. 1.0 sec.

Preset Sound F. Large Knob 4-- 2.5 sec. 4.3 sec. 1.8 sec.

Sound F. Large Knob -0- 2.1 sec. 4.5 sec. 2.4 sec.

Preset Sound F. Large Knob -o- 3.5 sec. 7.5 sec. 4.0 sec.

Band Preset Sound F. Large Knob 4-- 4.4 sec. 8.8 sec. 4.4 sec.

i Band Preset Sound F. Large Knob -o- 5.6 sec. I 11.5 sec. 5.9 sec.

Table 9.1: Means of the experimental conditions in seconde, sorted by the increase in seconde due to the Dual Task condition.

91

T.he order in which the task-parts were affected by the Dual Taak condition, from least to most, is depicted in Table 9.2

1. P-Loud 2. S.Functions L.knob 4--3. Ast-P 4. P.S.Functions L.knob 4--s. s.Functions L.knob -0-6. P.S.Functions L.knob -0-7. Band.P.S.Functions L.knob 4--8. Band.P.S.Functións L.knob -o-

Table 9.2: The order in which the task-parts were affected by the Dual Task condition (from least to most) •

It can be seen in Table 9.2 that in the Dual Taak condition, the performance of the task-part Band.P.S.Functions L.knob -0- was slowed down most. This effect was to be expected, sine~ this task-part contained a visual component: the subjecte were asked to adjust the sound functions back to neutra!. In order to do so, the subjecte had to look at the display of the car radio. This "visual component" was present in three of the four most affected task-parts namely:

• s.Functions L.knob -o-• P.S.Functions L.knob -o-• Band.P.S.Functions L.knob -0-

As stated in section 8.2.1, within the Dual Task condition the [FM/AM]2 task series differs significantly from the FM, AM and [FM/AM]1 task series at 0.05 level as well as at 0.01 level. This means that the [FM/AM]2 task series in the Dual Task condition were especially affected, compared to the FM, AM and (FM/AM]1 task-series. The [FM/AM]l as well as the [FM/AM]2 task series contained a larger number of eperation steps than the FM and AM task series. The [FM/AM]2 task series, however, differed from the [FM/AM]l task series regarding the fact that it consistedof radio çontrol tasks that contained the visual component. In other words, the presence of the visual component in a radio control task resulted in a significantly slower performance in the Dual Task condition oempared to the task series in the Dual Task condition where the visual component was absent.

It, thus, seems that the s;esence of a visual component in an operatien sequence bas an important effect on the speed with which the sequence is performed. The performance of the sequence is slowed down as a result of the visual component.

92

9.2.2 Number of operatien steps of the Task-parts

In Table 9.3 the numbers of operatien steps that constituted each task-part are added to the relevant task-parts.

Task-part Number of eperation steps

1. P-Loud 2 2. S.Functions L.knob 4-- 2 3. Ast-P 2 4. P.S.Functions L.knob 4-- 3 s. S.Functions L.knob -0- 2 6. P.S.Functions L.knob -0- 3 7. Band.P.S.Functions L.knob 4-- 4 8. Band.P.S.Functions L.knob -o- 4

Table 9.3: The number of eperation steps that constituted each task-part.

It can be seen in Table 9. 3 that the order in which the task-parts were affected by the Dual Task condition is reflected in the number of eperation steps that constitute each task-part: the least affected task-parts contain the lowest number of eperation steps, the most affected task-parts contain the highest number of operation steps. The only exception to this rule is the task-part s. Functions L. knob -0- which has been affected more than the preceding task-part, but contains less operation steps. However, this task­part contains the, earlier mentioned, visual component which forced the subjecte to look at the display of the car radio.

Thus, it seems that next to the presence of a visual component in an eperation sequence, the number of eperation steps in an operatien sequence has an effect on the speed with which the sequence is performed: the more operation steps the sequence contains, the more the operation speed is slowed down.

9.2.3 Possible effect of the lengthof the original radio control task on the performance of the task-parts

Table 9.4 contains the average increase in seconde of the mediane of the FM, AM and FM/AM task-parts in the Dual Taak condition. From now on, the [FM/AM]l and [FM/AM)2 task-parts will be referred to as [FM/AM]l+2.

FM AM [FM/AM]l+2

I Average increase 0.9 sec. 1.1 sec. 3.1 sec.

Table 9.4: Average increase in seconde of the median of the FM, AM and [FM/AM)l+2 task-parts in the Dual Task condition.

According to Table 9.4 the FM task-parts were, on the average, least affected in the Dual Task condition (average increase is 0.9 seconde), whereas the [FM/AM]l+2 task-parts were affected most (average increase is 3.1 seconde).

93

This finding is also illustrated in the final row of Table 9.5 in which the · average increases of the mediane of the FM, AM and [FM/AM]1+2 task-parts due to the Dual Task are depicted in percents. According to these data the mediane of the (FM/AMJ1+2 task-parts are, on the average, increased with 115%, whereas the mediane of the FM task-parts as well as the AM task-parts are increased, on the average, with 52%.

Task-part Increase of the mediane in \

FM AM [FM/AM)1+2

P-Loud 40\ 107%

S.Functions L.knob 4-- 10\ 75% 78%

Ast-P 10\ 20% 100\

P.S.Functions L.knob 4-- 40\ 108\

S.Functions L.knob -0- 137% 68% 158%

P.S.Functions L.knob -0- 70% 164%

Band.P.S.Functions L.knob 4-- 100%

Band.P.S.Functions L knob -o- 105%

Average increase in % 52% 52% 115%

Table 9.5: Increase of the mediane of the FM, AM and [FM/AM]1+2 task-parts in percents, in the Dual Task condition.

Thus, although the [FM/AM]l+2 task-parts were identical to the FM and AM task­parts, the average increase in the Dual Ta.sk condition is twice as high. Bowever, the [FM/AM]1+2 task-parts did differ from the FM and AM task-parts regarding the following fact. The [FM/AM]1+2 task-parts were taken from radio control tasks that took, on the average, longer than the radio control tasks in the FM and AM task series (see Tables 7.2- 7.5). In other words, in the {FM/AMJ1+2 task series subjecte performed radio control tasks that took longer than in the FM and AM task series. For instance, the [FM/AM]1+2 task series contained sequences consisting of four eperation steps. The maximum number of operatien steps in the FM and AM task series was three (see section 8.3: Task­parts).

This might suggest that the length of the original radio control task bas an effect on the speed with which the subsequent oparation steps constituting that radio control task are performed.

It is possible that the subjecte applied a different strategy with regard to the performance of the subsequent oparation steps that constituted the [FM/AM] 1+2 task series, as opposed to the performance of the subsequent eperation steps that constituted the FM and AM task series. It is not unthinkable that the subjecte performed the lengthier radio control tasks in the [FM/AM] 1+2 task series in chunks consisting of, for instance, two eperation steps in order to be able to cope with the dual task situation.

94

In other words, after having performed one chunk subjecte might have concen­trated on the computer screen again and continued the performance of the radio control task after having reacted to the response stimulus. Perhaps, by performing the radio control tasks in the [FM/AM]l+2 task series in chunks, instead of performing the radio control task as a whole, the subjecte felt they were more able to react adequately to the reaction time task as well as performing the radio control tasks correctly. As a result of this, hypotheti­cal, strategy the time needed to operate the radio control tasks in the [FM/AM]l+2 task series increased as opposed to the performance of the radio eontrol tasks in the FM and AM task series.

Since no statistica! tests were executed in order to verify this theory, further investigation is suggested bere.

9.3 The operatien of the function Automatic Tuning

As stated in section 8.6.1 the subjecte suffered difficulties during the eperation of the function Automatic Tuning. Now and then it took quite some time before the radio had tuned to a new station. Whenever, for instance, Bass level had to be adjusted, directly following the eperation of Automatic Tuning, the internal processor of the radio did not piek up the operatien of the Bass button. As a result, the processor only picked up the operatien of the Large knob. As a result, the yolume level was increased or decreaeed unexpectedly.

To overcoma this problem, two solutions are suggested bere:

1.) A buffer function that can store two or three button operations.

2.) Modification of the internal processor: while the processor is busy with the execution of function "A", parallel processing can facilitate the execution of function "B".

9.4 The eperation of the Loudness function

As stated in section 8. 5.1, subjecte experienced difficulties with the operatien of the Loudness function. In the Single Task condition, two activation errors occurred, whereas in the Dual Task condition, ten activatien errors occurred. It seems that in a situation where the Loudness button has to be operated relatively quickly, activatien errors are more likely to occur.

95

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