Lexical recognition of embedded unattended words: Some implications for reading processes

Acts Psychologica 47 (1981) 267-283 0 North-Holland Publishing Company

LEXICAL RECOGNITION OF EMBEDDED UNATTENDED WORDS: SOME IMPLICATIONS FOR READING PROCESSES *

Geoffrey UNDERWOOD Dept. of Psychology, University of Nottingham, England

Accepted August 1980

Two questions were addressed by these experiments. Firstly, do unattended words influence attended words only when they appear in isolation and thereby may attract attention, or are they influential even when embedded amongst ineffective material? Secondly, can the influence of an unattended display be increased by increasing the number of potentially effective words. By having observers give category names to attended words at the same time as masked unattended words appeared in a column to the right of fiiation, experiment 1 found that a single word was effective even when embedded, and that an increasing effect was not observed with a display with a 50 msec duration. There was some evidence of a linear increase in the size of the effect with a 200 msec display, but evidence from experiment 2 suggests that subjects may have been aware of the unattended words when they were exposed for this duration. The results were discussed in relation to a model of eye-fixation control during reading which postulates that unattended words gain lexical recognition when they are semantically related to the attended activity. This lexical recognition may then serve to mark interesting locations in the text and attract future eye-fixations.

It may now be concluded with some confidence that words may be recognized in the absence of their being attended. By observing the effects of unattended words upon the processing of attended messages, Corteen and Wood (1972), Lewis (1970), and MacKay (1973) have demonstrated that the meanings of individual spoken words can be recognized when those words are in unattended messages. Semantic variations in the unattended words are sufficient to produce changes

* These experiments were performed whilst the author was on leave of absence, and were gener- ously supported by the Department of Psychology, University of Guelph, Ontario, Canada. Thanks are due to Holly Cole for preparing the stimuli and running the experiments. Among those who have made useful comments on the experiments, I should particularly like to thank D.A. Allport, E.C. Dalrymple-Alford, P.O’B. Holt, and M.L. Matthews. Summaries of the experiments were described at the meeting of the Experimental Psychology Society, Oxford, July 1979, and preparation was supported by Medical Research Council grant G978/1173/N.

Correspondence should be addressed to Geoffrey Underwood, Department of Psychology, University of Nottingham, Nottingham NG7 2RD, England.

267

268 G. C~ruierwwxl / L~~sicol rcco,yrlitim of‘ embedded urratterlded uords

in the listeners’ performances. A similar case can be made for printed words from the evidence of Bradshaw (1974) and Underwood (1976, 1977a, 1980), suggesting that the effect is one involving the central organization of lexical access, and not restricted to a particular modal- ity of access.

Although many of our conclusions about the relationship between attention and language comprehension are derived from dichotic listening tasks, there is some evidence to suggest that they may be general- ized to the task of language comprehension through reading. Experi- ments reported by Bradshaw (1974) and Underwood (1976, 1977a, 1980) have demonstrated that the meanings of individual printed words may be effective even though these words were unattended, and Marcel (in press) has shown that words presented under subliminal conditions may still give an indication of their semantic processing. In a similar study reported by Allport (1977), subjects denied having seen an unattended word which had previously influenced their success at report- ing a briefly presented word. The ‘selective reading’ experiments by Wil- lows and MacKinnon ( 1973) and Willows ( 1974) go further, and suggest that unattended words may influence comprehension when reading prose. In a more exact study, Kennedy (1978) demonstrated that the meaning of an individual word could be appreciated before being fixated by the reader’s eye, again during the reading of sentences.

If the effect of a single word, upon an attended word, is of any general significance during reading, then it is perhaps representative of a phenomenon in which the material being fixated is not the only material being read. On the basis of the effects of unattended words we may speculate alternatively that non-fixated words are integrated with the reader’s schema (an hypothesis consistent with the data of Willows and MacKinnon), or perhaps used to guide future eye-movements (an hypothesis consistent with Kennedy’s data). These hypotheses will be discussed later, but both assume that unattended words are recognized during reading, and that once recognized they influence the reader’s behavioy, without the reader necessarily being aware of the recognition process or of its effects.

The justification of the present experiments comes from two sources, one of which relates to the possible use of unattended words during reading, and one of which relates to the possibility of increasing the extent of the effect by increasing the number of effective words.

If a single word, some way from the point of fixation, is able to

G. Underwood/Lexical recognition of embedded unattended words 269

influence the reader when that word is embedded spatially in ineffective or non-potent text, then a similar effect should be demonstrable during a single fixation. (The terms ‘potent’ and ‘non-potent’ are used here to refer to stimuli which may, or which may not, influence the processing of another stimulus. Thus, in a Stroop task, a potent word would be a color-related word. In most of these cases, a potent stimulus is one which is semantically related to the attended stimulus, but this is not always so. For instance, in Underwood’s (1976) picture-naming task the potent unattended word was either semantically related to the picture, or was semantically unrelated, depending upon the attentional strategy imposed upon the subject.) The influence of a single unattended word upon an attended word, in a tachistoscope experiment, may have some relation to normal reading. If so, the effect should still be present when the unattended word is embedded spatially, as it would be during normal reading. In the present experiments a single potent unattended word was contained in a display with three non-potent words. In this case, it is assumed that a potent word would be one which is semantically related to the attended word, on the basis of previous experiments in which the subjects were able to fixate the attended word during presentation (Underwood 1976: experiment l? 1977a).

If there is no effect of a potent word when it is embedded amongst non-potent words in the unattended display, then we may have a phenomenon similar to that reported by Mowbray ( 1964) regarding the presence of isolated unattended words. Mowbray had his listeners shadow a list of words, and remember any words presented to the unattended ear. The unattended words were presented to an otherwise silent earphone, and were reported only at the expense of performance on the shadowing task. Subjects were required to listen for words on the second channel, but these words were presented in isolation, and whether they were reported or not, they disrupted performance of the primary task. The disruption could have resulted from a re-orienting of attention to a new input on an otherwise silent channel. If this is the case, then any unattended stimulus which is presented in isolation may lead to a re-orientation and analysis of the stimulusfollowing the redis- tribution of attention. This is a problem to be aware of when inter- preting the results from a large number of investigations of selective attention, including those of Bradshaw (1974), Lewis ( 1970), MacKay (1973), Norman (1969). and Underwood (1976, 1977a). In these

270 G. Underwood /Lexical recognition of embedded utlattended words

studies it remains a possibility that an isolated stimulus resulted in a re-orientation of attention, and that a potent unattended stimulus gained the scrutiny of the attention process at least for a short time. There exist a number of studies which demonstrate an effect of unattended words which are not presented in isolation (Corteen and Wood 1972; Smith and Burrows 1974; Smith and Groen 1974;Traub and Gef- fen 1979; Underwood 1977b; Yates and Thul 1979), and so this criti- cism does not apply universally to studies of attention. Evidence from the semantic priming task used by Fischler and Goodman ( 1978) suggests that the effect of a priming word upon another word is greater when the prime cannot be reported. Although this result is from a task in which the words were presented successively, if we can generalize to the case of the effects of unattended priming words, then we may expect that unattended words will be most effective when there is no re-orientation of attention to them. The present experiment seeks to provide evidence of an effect in circumstances where it is unlikely that re-orientation would occur, by presenting a potent word in an unattended display consisting of a number of non-potent words.

To further reduce this risk, the unattended display was masked in these experiments by a random noise mask which was absent from display only when the stimulus field was displayed. Also, two exposure durations were used during the experiment, 50 msec and 200 msec. Whereas a re-orientation effect may be possible with the longer exposure, it is less likely with a masked presentation of 50 msec duration, and so any differences in effects from these two conditions may be indicative of an attentional change.

A secondary interest of the present study concerns the possibility of increasing the extent of the effect of the unattended display by increasing the number of potent words in the presentation. A single potent word may create a fixed and quantifiable amount of disturbance which is measurable in terms of the time taken to respond to the attended word. Given that, then we may ask whether the disturbance can be increased by the presentation of more than one potent word, and if so, then is the relationship between the number of potent words and the extent of disturbance a linear one?

To summarize the aims of these experiments, the method of investi- gating the relationship between language processing and attention is to assess the influence of unattended stimuli upon an attended activity. Influential, or potent, unattended words are, in general, those with a

G. Underwood /Lexical recognition of embedded unattended words 211

semantic relationship with the attended words. In the present experiments we are asking whether a potent unattended word is effective when it is present amongst a set of non-potent words. If not, then we may be able to ascribe some of the previously reported effects to a prin- ciple of distraction caused by an isolated stimulus, rather than to a prin- ciple of the semantic processing of unattended words. If the effect is robust under this manipulation of embedding, then an argument remains plausible which suggests that non-fixated words may be recognized during the reading of text, and that these ‘unattended’ words influence the comprehension of the text or future patterns of eye fixations. The final aim of the experiments is an investigation of the process responsible for the effects of unattended words. An unattended word may result in a fixed and small change in the response latency to an attended word, but alternatively, the effect may be an incremental phenomenon, and the presentation of an increasing number of unattended stimuli may result in an increasing change in the response latency. This manipulation was achieved in the present experiments by increasing the number of potent words in the unattended display, to observe their effect upon the processing of an attended word.

Experiment 1

Following the tachistoscopic presentation of each fixated word, the Ss were required to perform two tasks, to attend to and give the category name of the fixated word, as quickly as possible, and to then report as many of the non-fixated words as possible. The purpose of the second dependent measure was to distinguish, as far as possible, between those occasions where the observer was aware of an ‘unattended’ word, and those occasions where the unattended word was influential without awareness. To ensure processing of the fixated word a category naming task was used in preference to a word naming response, because the latter may be performed without processing the meaning of the word, possibly by employing grapheme-phoneme correspondence rules stored outside of the semantic lexicon (Coltheart 1978). The effect of unattended words in this experiment is dependent upon semantic processing of the attended word.

Method

Apparatus and materials

Each of the 50 trials of the experiment required the S to respond to a word by giving its category name. Five categories were used, with five instances of each category each tested twice. The five categories were animals, colors, clothing, parts of

272 G. Underwood / Lexical recognition of’ernbedded utzattetlded words

the body, and methods of trunsport, and the five instances of each category were the five most popular responses in Battig and Montague’s (1969) instance-genera- tion task.

The category instances which were to be fixated by the S, were printed to the left of the centre of blank tachistoscope cards using Letraset sheet number 193 (16 pt. Futura Medium), lower case lettering. To the right of the centre were printed four letter-strings, one above the other, using the same lettering method. These letter-strings were words, non-words, or combinations of both. The principal fea- ture of the design was the manipulation of the unattended stimuli, the four letter- strings which were printed to the right of the centre on the tachistoscope cards. To assess the effects of the related words, or potent words, two control conditions were used. In one of these all of the unattended words were unrelated to the fixated word (they were instances of the other categories used in the experiment), and in the other control condition the unattended items were non-words (they were taken from Hirata and Bryden’s (197 1) list of fourth-order approximations to En- glish). It is necessary to employ two control conditions to assess the effect of a related word, in order to assess the direction of the effect. To know whether a difference between related and unrelated words is really a facilitation caused by one, or an interference caused by the other, we need a third set of trials in which neither interference nor facilitation is possible. These neutral trials are provided by the unattended non-words in the present experiment. Thus, one factor was the type of background or control stimuli, and this factor has two levels, unrelated words and non-words. The second factor was the number of related words in each set of four- letter strings. This factor had five levels, as there were 0, 1, 2, 3 or 4 words related to the fixated word. Related words were the other instances of the category being tested on that trial. In those cases where 1, 2 or 3 related words were included in the unattended list, the positions of the words in the list were randomized.

As there were five categories being tested on two factors, one with two levels and one with five levels, this accounts for the 50 tachistoscope cards which were necessary. A further five cards were prepared for use in pre-experimental practice.

The stimuli were displayed using a Scientific Prototype N-900 tachistoscope, in which the visual angle subtended by the nearest letters of the fixated and non-fixated displays was 3”. The vertical visual angle subtended by the column of non-fixated letter-strings was 3;“. The fixation field of the tachistoscope displayed a visual noise masking stimulus which occupied the whole field except for an area slightly larger than that of the fixated word. No part of any fixated word came within 1” of the masking stimulus. All of the non-fixated letter-strings were presented to the same apparent location of the mask. Operation of the tachistoscope terminated the masking stimulus and displayed the test field as well as starting a millisecond timer. Offset of the test field coincided with the re-appearance of the masking stimulus. The timer was terminated by the operation of a voice switch connected to a micro- phone suspended near the Ss throat.

Procedure

TWO equally sized groups of Ss were used in procedures which were identical but for the durations for which the test field of the tachistoscope was exposed. The two


exposure durations were 50 msec and 200 msec, and each S saw all 50 trials at a constant exposure duration according to whichever group he or she had been ran- domly allocated. The 50 trials were presented to each S in a different randomized order. To reduce the possibility of repetition effects, categories were not re-tested unless the testing of two other categories had intervened.

Each S was informed that on each trial of the experiment they would see a single word printed in the white area of the fixation field. Upon exposure of this word they were to give the category name of the word as quickly as possible, for their response time was measured. Ss were told of the five category names used in the experiment, and a list of the five names was taped to the side of the tachistoscope hood. They were also informed that on some occasions ‘distracters’ would be printed to the side of the fixated word. Ss were instructed to ignore these words, but to report any which they could remember, after giving the category response. After each trial they were informed of their response latency. The intertrial interval lasted for the few seconds which it took for the response latency to be recorded and for the stimulus to be changed.

Subjects

The volunteers for the experiment were 28 undergraduate students enrolled for introductory psychology courses at the University of Guelph. All were right-handed and 18 were female.

Results

Ss presented with 50 msec exposures made fewer than 4% errors on the category naming task, and those with 200 msec exposures made fewer than 3% errors.

Analyses were performed on two forms of data, the response latencies in the category naming task, and the numbers of unattended words which were reported. Following the criticisms of Wike and Church (1976) concerning Clark’s (1973) argument for the consideration of linguistic stimuli as random effects, the present analyses do not employ the min F’ statistic.

Each S contributed 10 scores to the analysis of variance matrix for the analysis of category naming latencies. These were the scores from the 5 X 2 design, with five levels of the ‘number related words’ factor, and two levels of the ‘type of background letter-string’ factor. Each S produced five latencies for each of these ten cells, but errors were excluded from the means, and so were latencies from those trials on which the S was able to report an unattended word. Thus, the analysis was concerned only with error-free responses from trials where the unattended words were unavailable for later report. The means from this analysis are presented for the two groups of Ss in fig. 1. The analysis of variance indicated that the only main effect to produce reliable differences was type of background item, with non- words being associated with faster responses than unrelated words (F( l/26) = 4.29, p < 0.05). Neither exposure duration (F < 1) nor number of related words (F < 1) led to overall differences. The only significant interaction term to emerge from the analysis of variance involved the ‘backgrounds’ and ‘number of related words’ factors (F(4/104) = 11.47, p < 0.001). Inspection of fig. 1 suggests that the source of

214 G. Underwood /Lexical recognition of embedded unattended words

\;_ri:, : I 0’

rc v- :/

Y EXPOSURE DURATION

1

<

--i L I I I I I

0 1 2 3 4

NUMBER OF RELATED WORDS IN THE UNATTENDED DISPLAY

Fig. 1. Mean response times for categorisation of the fixated (attended) words as a function of three factors: exposure duration, type of materials in the unattended display, and number of semantically related words in the unattended background display.

the interaction is the contrast between the effects of few related words and many related words in the unattended display. Whereas no related words, and possibly one related word, are experimental conditions which result in wide differences between the effects of background items, the presence of more related words has the effect of eliminating these differences.

Analyses of trend were performed on the four curves present in fig. 1 using two sets of contrast coefficients for each curve, one of which was a linear contrast, and the other was a dogleg contrast with the break occurring at one related word in the unattended display. Thus, the coefficients for the linear contrast were +2, +l, 0,


Table 1 Mean numbers (with standard deviations in brackets) of the unattended words reported after

each successful categorisation response to the attended word in experiment 1.

50 msec exposure

Words in Nonwords in background background

200 msec exposure

Words in Nonwords in

background background

Related words reported 0.3 0.0 (1.2) (0.0)

Unrelated words reported 0.0 0.0 3.3 0.3 (0.0) (0.0) (4.21 (1.2)

-1, -2 (for the two curves with unrelated words in the background; signs were reversed for the two curves with non-words), and the coefficients for the dogleg contrast were +4, - 1, - 1, - 1, - 1 (for unrelated words). For unrelated words in the background, at 200 msec exposure, both the dogleg contrast (F(4/52) = 12.84, p < O.OOl), and the linear contrast (F(4/52) = 11.08, p < 0.001) provided acceptable descriptions. For unrelated words in the background, at 50 msec exposure, the only set of contract coefficients to provide a suitable fit were those which matched the dogleg (F(4/52) = 3.85, p < 0.01). For non-words in the background, at 200 msec exposure, the dogleg (F(4/52) = 9.46, p < O.OOl), and the linear contrast (F(4/52) = 14.39, p < 0.001) were acceptable. For non-words in the background, at 50 msec exposure, the dogleg (F(4/52) = 18.74, p < 0.001) and the linear contract (F(4/52) = 9.94, p < 0.001) again were both acceptable.

When the latency data were analyzed from those trials on which Ss were able to report any of the unattended words, no main effects and no interactions proved to be statistically reliable.

The mean numbers of unattended words to be reported, after each categorization response, are presented in table 1. These data were not submitted to an analysis of variance because of high variance between Ss. The only comparison of interest, that between the number of related and unrelated words to be recalled, reveals very similar mean numbers of words recalled x2( 1) < 1.

Discussion

This discussion will be restricted to comment upon the immediate implications of the results of experiment 1, and a general discussion of the wider implications will follow the description of experiment 2, which is a control experiment against which the recall data of experiment 1 may be compared.

The analysis of the latency data represented in fig. 1, indicates that for all four curves reliable dogleg matches could be obtained. These matches confirm the pre- diction that the presence of a single related word is sufficient to affect the proces-

216 (;. Underwood / Lexical recognition of embedded unattended usords

sing of the unattended word. This suggests that the effect is not a result of an isolated stimulus attracting attention before the response to the fixated stimulus has been completed. Two routes of processing may be suggested as being responsible for the effect caused by the unattended words, and these may be termed the !zoh- selective access and contextual facilitation hypotheses.

The non-selective access hypothesis argues that all unattended words non-selectively gain lexical access, and in this sense are recognized. Awareness is not a necessary correlate of recognition, for the result here is reliable for only those trials where awareness was not reported. After lexical recognition of a potent word then interference or facilitation may proceed according to the task demands. By this hypothesis the influence of unattended upon attended words may occur either before or after recognition of the attended word. However, the law of prior entry would lead us to expect that the attended word would already have been recognized by the time the unrelated word was available. After lexical recognition of the attended word, semantic analysis is necessary for the process of categorization prior to the organization of the response.

Interference may occur during categorization or response organization, but the difference between response latencies when the unattended display contained four unrelated words or four non-words provides us with a basis for distinguishing between these suggestions. Fig. 1 indicates that the slowest responses came when four unrelated words were present in the unattended display, and that the fastest responses occurred with four non-words in the display. A display with four related

words as the unattended stimuli results in a categorization latency some way between these two extremes. Why should four unrelated words produce latencies greater than those associated with four non-words? The most likely explanation is that they were not unrelated to the task, and indeed the words chosen as ‘unrelated words’ were all words used on other trials in the experiment. They were words which the observers were required to recognize on other trials. In this sense the ‘unrelated words’ were not entirely unrelated to the task to which the Ss were attend- ing, although the specific words were not semantically related on a normative scale. These short-term task associations may be responsible for the elevated response latencies with ‘unrelated’ words in the unattended display. If this is the case then the locus of interference might be expected to be during a stage of processing during which the catel:ory name was selected from amongst the five names available. At this stage the ‘unrelated’ words would, if recognized, provide conflicting information in a classic Stroop-like relationship. The addition of a single related word would reduce the extent of the interference effect by providing supporting information for the categorization of the attended word. If the foregoing analysis is correct, then we may conclude that unattended words cause their effects after the lexical recognition of the attended word, but prior to the completion of semantic .analysis.

The contextual facilitation hypothesis of the effect of unattended words suggests that not all unattended words are recognized. Following lexical analysis of the attended word its associates would be primed by a ‘spread of activation’ in the lexicon (Collins and Loftus 1975; Fischler and Goodman 1978; Meyer and Schvane- veldt 1971). This activation is seen by Meyer et al. (1975) as having a facilitating


effect upon the encoding of the semantic associates of the activated word, which might then require less stimulus information for recognition. If an attended word produced a spread of activation when it is recognized, and if this activation facih- tates the processing of its associates, then any unattended words which are related to the attended word would gain more activation than would unrelated words. The contextual facilitation of the recognition of related words would then feed back and influence the post-recognition processing of the attended word. By this model, the locus of interference would again have to occur after the lexical recognition of the attended word. The stage of categorization would be the likely locus of interference by the same reasoning as applied with the non-selective access hypothesis.

The selective influence of unattended associates upon attended words in other studies goes some way to suggesting that if we can choose between these two hypotheses of recognition, then it is the contextual facilitation hypothesis which is the more credible. The experiments reported by Corteen and Wood (1972), Lewis (1970), and Underwood (1977a, 1980) indicate effects dependent upon the selective processing of associates. The present experiment, and that of Underwood (1976: experiment 2), both indicate that under some circumstances the non-selective access hypothesis must be considered as viable.

The following experiment, designed as a comparison for experiment 1, is a further investigation of the recognition of the words which were described as being ‘unattended’.

Experiment 2

Whereas in the previous experiment Ss were told to consider as distracters the four words to the right of the fixated word, but to report them if they ever saw them, we cannot be sure with these instructions if the Ss could use the two demands inde- pendently. Once told to ignore some words they may not report them either because they were ignored and therefore unavailable, or because they were expected not to see the words. The unattended words may have been seen, but their report may have been suppressed by the bias in the experimental instructions. Accordingly, the present experiment investigates what the Ss can report in the absence of prior instructions to ignore the unattended words. No categorization instructions were given, but otherwise the experiment is identical to experiment 1. The task was to report all five words in each display, with the single unmasked

word to be reported first.

Method

Apparatus and materials

The 50 trials of the experiment required the same apparatus and materials as were used in experiment 1, except that the timer was not employed.

Procedure

Two groups of Ss were used, and received treatments which were identical but for the durations for which their stimuli were exposed. One group saw the words

278 G. Underwood /Lexical recognition of embedded unattended words

for 50 msec, and the other group for 200 msec. Allocation of the Ss to the two groups was made on a random basis.

Ss were informed that on each trial they would see five words, which they were

to report immediately following offset of the display. They were to report first the word printed in the white area of the fixation field, followed by the other words in any order. Ss were informed that only when they reported the isolated word cor- rectly would the other recall data be scored (as was the case), and so they should be sure to remember that word.

Subjects

The volunteers were 28 undergraduate students enrolled for introductory psychology courses at the University of Guelph. All were right-handed, 15 were female, and none had participated in experiment 1.

Results

The recall data for the masked words from the two groups of Ss contained no errors in the recall of the unmasked word, and are presented in table 2. The treatment by which Ss received a 50 msec presentation of words resulted, effectively, in very few of the masked words being recalled. In none of the four conditions did the rate of recall reach l%, and so no further analysis was performed. The data from the 200

msec treatment were analyzed together with the comparable data from experiment 1 in a three factor analysis of variance (experiments; unattended backgrounds; type of word recalled).

All three main effects proved to be reliable in the analysis of variance. More words were recalled in experiment 2 than in experiment 1 (F(l/26) = 26.72, p < O.OOl), more words were recalled which were related to the fixated word than were those which were unrelated (F( l/26) = 28.55, p < O.OOl), and more items were recalled when the background items were words rather than non-words (F( l/26) = 5.17, p < 0.05). The only interaction to prove reliable was that between the two

Table 2 Mean numbers (with standard deviations in brackets) of the words reported after successful report of the fixated word in experiment 2. These are the words which are described in experiment 1 as being unattended.

50 msec exposure


200 msec exposure


Related words reported 0.3 0.7 35.9 38.6 (1.2) (1.6) (16.5) (17.2)

Unrelated words reported 0.1 0.0 22.5 10.8 (0.8) (0.0) (20.7) (15.6)


factors of experimental instructions and the association of the attended word (F( l/26) = 6.36, p < 0.05), with the improved recall of related words (over unrelated words) being more evident in experiment 2 than in experiment 1.

Discussion

Although more words were recalled in experiment 2 than in experiment 1, we cap- not be certain as to whether this is an effect of instructions to attend selectively in experiment 1 causing a change in the reception of the non-fixated word, or a change in the bias to respond. Moray and O‘Brien (1967) did demonstrate a change of reception, as indicated by a change in d’, when the attentional instructions were manipulated, but our tasks may not be comparable. Experiment 2 does indicate that when Ss are given specific instructions to report the words printed in a column on the right, they are successful only with the prolonged exposure duration. With a 50 msec exposure, recall was of a similar level as that in experiment 1. Thus, even with instructions to report the column of words, Ss were unable to do so, suggesting that the effects of these words in experiment 1 were produced indepen- dently of their availability to awareness.

The substantial level of recall of words with a 200 msec exposure enforces a qualification to any conclusions about their effects in experiment 1. If the words could be recalled, then we cannot know whether they were available to awareness in experiment 1, but their report repressed by instructional bias. Although this may seem unlikely, it remains as a possibility.

The difference in recall rates between words related and unrelated to the fixated word is a replication of an effect reported by Underwood (1977a). Unattended words related to an attended picture were reported more often than words unrelated to the picture, after the picture had been named.

General discussion

The recall data of experiment 2 suggest that, at least for the 50 msec exposure conditions, observers are unable to report words which are influencing them in experiment 1. We have a suggestion of this result from earlier studies (e.g. Bradshaw 1974; Corteen and Wood 1972; Un- derwood 1977a), but in the present case there is evidence that the unattended words could not be reported even when the subjects were instructed to report them as a primary task. Given that the unattended words were having an effect without the volition of the observers it is possible to conclude that the answers to the two queries set out as the justifications for the experiment are as follows.

The first question was whether a single potent word embedded in an unattended display would be effective upon the processing of the

280 G. Underwood / Lexical recognition of’ embedded unattended utords

attended word, or whether previous effects have been due to an isolated stimulus capturing attention momentarily. In experiment 1 the addition of a single potent word to an otherwise non-potent display was indeed sufficient to affect the categorization latency of the attended task. Whereas this conclusion holds for both exposure durations, it is not clear whether the observers were aware of the unattended words with the 200 msec exposure, and so the effects may have been due to the volitional processing of those words. For the 50 msec exposures however, it appears that the effects were a result of a process which was independent of the direction of attention.

The second question concerned the possibility of increasing the influence of unattended words by increasing their number. When contrast coefficients were matched against the number of related (potent) words in the analysis of categorization times, it was found that dogleg contrasts tended to provide the best fits for the 50 msec exposures. The dogleg curve suggests a singular effect which can be elicited by the presence of a potent word, but that additional potent words have no further effect. A linear curve suggests that the effect can be increased by adding to the number of potent words, and linear contrasts were more successful with the data from the 200 msec trials than from the 50 msec trials. We have the possibility that observers were aware of the unattended words in experiment 1 when given exposures of 200 msec, and we have linear effects of potent words for this exposure duration. From these converging sources of evidence the hypothesis emerges that volitional priming may be increased when more stimuli are available, but that automatic priming is not incremental.

Do these and related experiments have any general implications, or are they laboratory demonstrations of unattended words affecting the processing of attended words? There is now a certain amount of evidence to suggest that non-fixated words do influence reading behavior, and that these unattended words may be integrated with the material being read (Willows 1974; Willows and MacKinnon 1973), and may be associated with future patterns of eye-fixations (Kennedy 1978). The influence of unattended words in the present experiments may derive from the usefulness of processing unattended words during reading. Willows (1974) reported that it was the good readers who showed the greatest effects of unattended words, and so it may be that one of the skills of reading which should be acquired is to accept unattended information. The alternative is that unattended words have their influence

G. Underwood / Lex!cal recognition of embedded unattended words 281

upon the skilled reader as a function of some other process, such as adopting a less-focussed strategy of attention whilst reading. If this is the case then unattended words are again causing interference which is not necessarily adaptive with respect to the goal of reading that which is being fixated. The result from experiment 1 provides a comment upon these two interpretations of the Willows result. If we can conclude that the observers were focussing upon the categorization task, and were unaware of the meanings of the unattended words, then the effect was not one which appeared as a consequence of adopting a divided strategy of attention (at least for 50 msec exposures). Accord- ingly, an effect can be observed when observers focus their attention upon the fixated material, and so the explanation of Willows’s result in terms of skilled readers only showing an effect as a result of their divided attention strategy, cannot be supported.

An alternative source of the effect in the skill of reading may be in the guidance of eye-movements, and this hypothesis is supported by Kennedy’s (1978) data. Reader’s eyes alight upon the second member of a pair of associates faster than would be expected, and remain there for longer than would be expected. If the semantic association can be appreciated prior to attention being directed to the two members, then here we have a function for the processing of unattended words which are related to attended words. This hypothesis is consistent with the contextual facilitation hypothesis of the mode of influence described above, and suggests that the associates of words being read are primed by the process of reading, and that it is the priming which facilitates their lexical recognition.

There exists some support for the notion that eye-movements are under the control of cognitive information from the work of Rayner (1977) and Rayner and McConkie (1976), in that fixation durations were influenced by the type of information being processed. Support for the notion that the location of fixations can be influenced by unattended information ahead of fixation, is less abundant. The result reported by Kennedy is valuable in this respect, and lends credibility to the extension of the process-monitoring hypothesis of eye-guidance favored by Rayner. Support may also be derived from another source of visual processing. Mackworth and Morandi (1967) found that whilst inspecting pictures, fixations tended to occur in areas of unpredictable or unusual information. Two explanations are possible. Either the whole picture was first scanned and only then were the interesting loca-

282 G. Underwood / Lexical rccog~~ition of embedded unattended words

tions investigated, or the observers knew that the locations were interesting before investigation. If the latter explanation holds, then we must explain how this information is available prior to fixation. The explanation offered here applies to both verbal and non-verbal visual processing, and considers that information presented to the parafovea of vision can be processed for meaning prior to its being attended. This pre-attentive processing may then attract the attention system which may be necessary for full integrative processing.

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Lexical recognition of embedded unattended words: Some implications for reading processes

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