On to the Applications
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Transcript of On to the Applications
ON TO THE APPLICATIONS
Mental Workload DEFINITION: The feeling of
mental effort or the level of use of the human operators limited resources.As task demand increases, resources left in
reserve decreases.When attentional resources are exceeded,
further increases in task demand will reduce performance.
New airplanes and military systems are analyzed in terms of mental workload.
Measuring or Predicting Workload
Time-Line Analysis: Measure amount of time spent on task relative to amount of time available. ○ 100% is all time available is being used. ○ Gives estimate of how time use changes during course of
task, e.g. flying.Dual Task Experiments
○ Primary Task measure: Change the nature of the main task and see how performance changes.
○ Secondary Task measure: Give a secondary task. Measure changes in its performance as the primary task is changed in difficulty.
Subjective Measures: self-report of users.These measures do not always correlate well.
Beginning a Task Analysis All designs begin with the goals and
purposes of the overall system.There are different levels of goals:
○ The function: an airplane moves things great distances in a relatively short time.
○ The job of the system: fighter vs. passenger jet.○ The level of technology: mechanical vs. electronic
instruments.○ The cost of the finished system.
These types of questions provide and overview and set up constraints.
Beginning a Task Analysis - 2 Relevant questions to keep in mind
Kantowitz and Sorkin, 1983 What inputs and outputs must be provided to satisfy system
goals? What operations are required to produced system outputs? What functions should the person perform within the system? What are the training and skill requirements for the
operators? Are the tasks compatible with human capabilities? What equipment interfaces does the human need to
perform the job? Does the human help or hurt the machine, vice versa?
Analysis of an Existing Job Process Analysis
Derived from the beginning of industrial engineering from the beginning of century.
Major goal: improve efficiency.○ issues of safety and human need are not important
here.Specifics:
○ Each act, movement of the human, is identified as a therblig.
○ The therbligs necessary for the job are identified.This technique allows for identification of wasted
movements that can be combined or eliminated.
Analysis of an Existing Job - 2 Principles of Motion Economy
A list of principles for job and workspace design to increase movement efficiency.
Examples:○ Use of Human Body:
Eye fixations should be as few as possible.○ Layout of Workplace:
Tools, materials and controls should be located close to the point of use.
Materials and tools should be located for best sequence of movement.
Analysis of and Existing Job - 3 Link Analysis
Analysis of sampling pattern of displays and controlsGoal: to arrange elements to make moving from one
display or control to another display or control more efficient and effective.
Collect Sampling Data:○ List of which elements are used or viewed in which
order○ Frequency Data: how often each display is viewed.○ Conditional Probabilities: given one display is viewed,
what is the probability that another display will be viewed next.
Analysis of an Existing Job - 4 Link Analysis (continued)
The probabilities can assist layout.○ If probability is high and element is important,
the display or control should be centrally placed.○ If a probability is high and importance is low
(that is, the designer wishes to reduce the probability) the element should be moved to the periphery.
○ If two displays or controls are used in sequence, that is their conditional probabilities are high, they should be next to each other.
Analysis of an Existing Job - 5 Critical Incident Technique
Essentially errors or near errors are recorded○ journals or interviews are used.
Since errors are often the result of design flaws, recording the errors can help analysis.
The record must be detailed or it will not be useful.
A large sample is necessary to see if errors are systematic, indicating a design flaw, or random, indicating human inattention.
Analysis of Job in Design Stage Hopkin’s Approach - a general plan
Analyze goals of job in terms of:○ purpose○ assumptions and constraints
Allocate functions○ general refers to assigning tasks to humans and
machines○ not easy.
Too much to human overloadsToo little to human bores and dehumanizes
○ Determine displays and controls
Analysis of Job in Design Stage - 2 Timeline Analysis
same as for determining workload. Failure Task Analysis
Analyze all anticipated failures to ensure that humans will be able to handle.
e.g. MD-11 In many cases, it is advisable to perform
more than one of these analyses.
Analysis of Job in Design Stage - 3 Types of Design Relative to Errors
Exclusion○ Design to make it impossible to commit errors○ Doubt this is really possible
Prevention○ Design to minimize the possibility of errors
Fail Safe○ Design to minimize the effects of errors
You can combine the last two
Anthropometry DEFINITION:
measurement of the human body and its biomechanical characteristics (Adams, 1989). Biomechanical refers to
the mechanical (machine-like) capabilities of the human skeleto-muscular systems.
Thus, this field measures our sizes and how we move and move easily.
Anthropometry - 2 The Need for Anthropometry
We are not all the same size. ○ If systems were designed to fit only one person, the few
if any would be able to use the system.Poor design for mechanical abilities of the human
body can lead to discomfort or injury, e.g., the height of keyboard for a computer.
Sources of Anthropometry DataTextTables in books on reserve
○ McCormick and Sanders○ Kantowitz and Sorkin
Examples of Anthropometric Data Static Measures
Passive measures of the dimensions of the human body.
These measures are used to determine size and spacing requirements of work space.
Example Measures○ height○ weight○ wing span○ seat to elbow height.
Examples of Anthropometric Data - 2 Dynamic Measures
Measures of the dynamic properties of the human body, such as strength and endurance.
These measures are used to match the dynamic characteristics of controls to user.
Measures○ range of motion for various joints○ force of leg pushes○ strength of fingers
How to Use Anthropometric Data Know your population
If your measures are from a different group than your users are from problems could result.○ Women are different from men.○ Asians are different from Americans.
Use Recent DataChanges in diet and habit lead to changes in size
and fitness of population○ Try on old suit of armor
Most size measures are done on nudes.clothes change our sizes
○ think of seat belts in summer vs. winter.
How to Use Anthropometric Data - 2 Techniques of Design
Design for extremes○ A standard is to design to fit 5th to 95th percentiles of the
population○ The chair is a common example.
Make the design adjustable○ Ideally this is optimal, especially if adjustment only needs to
be done once.○ If the adjustment is hard or must be done frequently, the
user may not do them.○ Airline pilots are require to do this for cockpit.
The techniques can be combined Always test the design
Requirements for Task Analysis Background Research
Determine GoalsInterview potential users to gain insight into their
needsLibrary Research on Design Issues
Structure of Task AnalysisDetermine flow of activityDetermine Possible Sources of Error/Frustration
PaperBackground and Task AnalysisGive Citations
Human Computer Interaction Issues to Cover
The WorkstationThe DialogueThe User Environment
The Workstation Perceptual Issues (The Visual Display Unit or
VDU)Luminance (Foreground - 35 cd/m2)Refresh Rate (Flicker)Contrast (Minimum ratio of 3/1)Legibility (Size, height/width ratio, and stroke
width)Polarity (Dark on Light is recognized easier, Bauer
and Cavonius, 1980)Chromatic DiscriminationVisual Fatigue (e.g., due to blurry letters)
The Workstation Antrhopometric issues
Display level○ We like to look down a little○ If we don’t, we can get neck strain and back strain.
Keyboard layout, level, and shape○ Stuck with QWERTY○ Angle of hands can cause problems. It is worse if the
keyboard is too high○ Split can help. Angle each of the hands out.
Mouse (and other related pointing devices○ Gain (movement of mouse relative to movement on screen)
Work area (e.g., place for papers books)
The Dialogue Mental representation of action of computer
from rules to modelsfrom specific steps to general expectations of
behavior User Interface
commands vs. menusrecall vs. recognitionMenus
○ Chunking and organization○ More organization vs. fewer substeps○ Flexability of use
The Dialogue - 2 Help and aiding interaction
Help vs. tutorials During use vs. before Online analysis of use with hints
Skill of User Menus, help, etc. are slow and relatively inflexible but easy to
learn○ Menus vs Ribbons vs Breadcrumbs○ Image (Icon) vs. Text
Commands (shortcut keys) are faster and more flexible but harder to learn
Thus skill level interacts with interface Hypertext - Embedded Commands Icons
The User Environment Lighting (internal and external)
Glare, and contrast and saturation reductionAdaptation related problems
Noise (from computer and others)Loss of concentration or disruption o f othersMasking of computer sounds
Support of useTraining and innovation
Unwilling usersAssuming the environment is dependent on computer
skill and use
Influence of the Web Factors to consider
Similar to All programs○ Distance
How provide help?○ Variation of environment
Room and other conditions veryUnique to Web
○ Variation of Setup, e.g. different browsers○ Limitations in Interface○ Loss of standardization