Journal of Experimental Psychology: Human Perception and Performance 1978, Vol. 4, No. 4, 674-690

Perceptual Flexibility in Word Recognition: Strategies Affect Orthographic Computation But Not Lexical Access Thomas H. Carr and Brian J. Davidson University of Oregon Harold L. Hawkins University of South Florida Four tachistoscopic forced-choice recognition experiments explored the flexibility of processes underlying word perception. Stimuli were words, orthographically regular but unfamiliar pseudowords, and orthographically irregular nonsense strings. In the first two experiments, subjects knew that several different kinds of stimuli Would occur in each block of trials and that one kind would occur much more often than the others. No matter which stimulus subjects expected to see most often, accuracy on words and pseudowords differed little, and both were identified considerably better than nonsense. In the third and fourth experiments, subjects were led to believe that only one stimulus type would occur but were surreptitiously shown another type on a small number of trials. Words were again identified more accurately than nonsense, and the size of the effect was independent of expectations. However, when either words or nonsense strings were expected exclusively, pseudoword accuracy did not differ from nonsense accuracy. Only when subjects knew that pseudowords would occur did they identify pseudowords more accurately than nonsense. This dissociation between word and pseudoword identification indicates the operation of two independent encoding mechanisms during tachistoscopic recognition, a stimulus-specific or logogenlike system sensitive to particular familiar strings and an orthographic mechanism sensitive to generally applicable constraints on letter sequencing. The stimulus-specific mechanism appears to be utilized automatically, but use of the orthographic mechanism is under strategic control. As shown in the first two experiments, however, rather extraordinary measures were required to demonstrate the flexibility of the orthographic processes used in this task.

When viewing time is severely limited, a word can be perceived more accurately than a random string of letters or even a single

letter presented in isolation (Carr, Lehmkuhle, Kottas, Astor-Stetson, & Arnold, 1975; Reicher, 1969; Spector & Purcell, 1977). Two quite different kinds of process-

This research was supported by National Institutes of Health Postdoctoral Fellowship 1-F32HD05157 from the National Institute of Child Health and Human Development to the first author under the sponsorship of Michael I. Posner, and by National Science Foundation Research Grant BMS75-09574 to the third author. We would like to thank Merton Church, Suzanne de Lemos, and Gayle Belsher for their excellent assistance in collecting data, Gerald M. Reicher and Michael I. Posner for consultation in beginning the project and comments on the manuscript, and the faculty and

in

£ mechanisms have been proposed to

students of the University of Oregon's Experimental Psychology Program for comments and criticisms offered during presentation of these results at two Program seminars. We owe a special debt to Jonathan Baron and an anonymous reviewer for their helpful criticisms. Requests for reprints should be sent to Thomas H. Carr, who is now at the Department of Psychology, University of Nebraska, Omaha, Nebraska 68182.

Copyright 1978 by the American Psychological Association, Inc. 0096-1523/78/0404-0674$00.75

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PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

explain this difference. The first, which can be called an orthographic mechanism, depends on structural regularities associated with patterns of spelling and pronunciation (Baron & Thurston, 1973; Gibson & Levin, 1975; Spoehr & Smith, 1973). Structural regularities are utilized by the perceptual apparatus to increase the efficiency of encoding processes prior to lexical access and semantic identification. In orthographic models, increased efficiency is usually thought to result from using units of analysis larger than the single letter in constructing an internal representation of the letter string (Aderman & Smith, 1971; Gibson & Levin, 1975; E. Smith & Haviland, 1972; Spoehr & Smith, 1973). Although exceptions have occurred in experiments in which a large proportion of the stimuli sound alike but are spelled differently (Baron & Thurston, 1973; Hawkins, Reicher, Rogers, & Peterson, 1976), the representations of words that are functional in tachistoscopic recognition seem to have the characteristics of a phonological or name-based code (Hawkins et al., 1976; Mezrich, 1973; Spoehr & Smith, 1973). Thus the orthographic mechanism considered here is probably concerned, at least in part, with spelling-to-sound translation. The second kind of mechanism depends upon the preexistence of entries for words in long-term memory (Becker, 1976; Keele & Neill, in press; Morton, 1969; F. Smith, 1971; Morton, Note 1). Contact is made between sensory information obtained from the stimulus and criterial information represented in the lexical entry or logogen, speeding the identification of letter strings possessing such entries. Details of the way in which contact is made vary from model to model, as do claims about what kind of code is made available by the entry's activation. All of these models, however, propose that knowledge about specific familiar letter strings rather than a set of generally applicable, rule-based operations facilitates word perception. This alternative to orthographic processing can therefore be called a lexical or stimulus-specific mechanism, bearing in mind that its output may be the same type of name code that is

675

produced in a quite different way by the orthographic mechanism (Baron & Strawson, 1976; Morton, 1969). Since utilizing orthography and utilizing lexicality are not mutually exclusive modes of processing, both may be involved in the word superiority effect. A critical type of evidence for deciding the relative importance of the two kinds of mechanisms is the comparison of processing efficiency for words with processing efficiency for orthographically regular but meaningless and unfamiliar pseudowords. If there were no difference between the two, one would suspect that orthographic or rule-governed mechanisms were entirely responsible for the special character of tachistoscopic word perception, since such mechanisms can be applied to words and pseudowords alike. If, on the other hand, performance on words were superior to performance on pseudowords, one would conclude that the existence of a lexical entry provides an additional advantage to perception. It is unfortunate for simplicity's sake that both empirical outcomes are available in the literature. Baron and Thurston (1973) reported no difference in recognition accuracy between words and pseudowords, while Manelis (1974) reported word advantages ranging from a statistically unreliable 2.9% to a significant 8.5% across three experiments. These studies each employed a version of the tachistoscopic forced-choice procedure developed by Reicher (1969). Two methodological differences, however, could have operated to diminish processing differences between words and pseudowords in Baron and Thurston's experiments relative to the experiments of Manelis. First, Baron and Thurston used words that, on the average, occur less frequently in the language than the words used by Manelis. Scarborough, Cortese, and Scarborough (1977) showed that low-frequency words require longer lexical access times than do high-frequency words, which might make the lexical mechanism less efficient for low-frequency words under demanding perceptual conditions. This could be tested by including a wide range of frequencies within a sample of word stimuli and com-

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paring performance on high- and lowfrequency words. Second, Baron and Thurston presented words, pseudowords, and orthographically irregular nonsense strings in a random mix, while Manelis used only words and pseudowords presented either in pure or in randomly mixed blocks. If there are strategic aspects to the operation of mechanisms used in word perception, this difference in the salience and predictability of words relative to other stimuli might account for the difference in results obtained in the two studies. Since considerable strategic flexibility has been attributed to the word processing system (Aderman & Smith, 1971; Hawkins et al., 1976; James, 1975; LaBerge, Petersen, & Norden, 1977; Neisser, 1967; Shulman & Davison, 1977; Tweedy, Lapinski, & Schvaneveldt, 1977), this seems a likely possibility. Identifying the extent to which orthographic and lexical mechanisms are under strategic control and respond flexibly to expectations generated under specific task demands would place some important constraints on a theory of word processing. The four experiments described in the present article, then, were designed primarily to investigate perceptual flexibility resulting from task-induced expectations and the role that flexibility might play in the identification of letter strings. We hoped as a result of this investigation to be able to say whether one or two encoding mechanisms support tachistoscopic recognition and to discover how much strategic control people have over the operation of the mechanisms. Experiment 1 varied the relative proportions of words and pseudowords in trial blocks consisting of words, pseudowords, and a small number of single letters. The single letters were included as a baseline against which to assess the relative magnitude of effects attributable to orthography, represented by the difference between pseudowords and letters, and any additional effects attributable to the existence of lexical entries, represented by the difference between words and pseudowords. In this experiment, subjects would always have reason to attend to orthography, but the incentive to attend to lexicality would

presumably vary with the proportion of words in the trial block. Therefore Experiment 1 was intended to demonstrate differential reliance on lexical or stimulusspecific information as a function of the likelihood that such information would prove beneficial. Experiment 1 Method Subjects. Eighteen volunteers from the Department of Psychology's paid subject pool participated in the experiment. Each received $2.00 for the 1-hour session. All were native speakers of English, with normal or corrected-to-normal vision. Materials. Three types of stimulus list were used: (a) high-proportion words, (b) high-proportion pseudowords, and (c) equal proportions of words and pseudowords. The high-proportion word list contained 96 pairs of words (48 of which were filler items), 24 pairs of pseudowords, and 24 pairs of single letters. Thus the entire list was 144 pairs long, of which two thirds were words, one sixth were pseudowords, and one sixth were single letters. The high-proportion pseudoword list contained 96 pairs of pseudowords (48 of which were fillers), 24 pairs of words, and 24 pairs of single letters. Two thirds of this list were pseudowords, one sixth were words, and one sixth were single letters. Except for word and pseudoword fillers and the single letters, all stimuli were obtained from Manelis (1974). Two random orders of each type of list were created. Since Manelis employed 48 pairs of words and 48 pairs of pseudowords, all of his word stimuli were used in the high-word and equal-proportion lists. All of his pseudowords were used in the equalproportion and high-pseudoword lists. For the high-word list, half of Manelis's pseudoword pairs were used in one of the random orders and the other half in the remaining order. For the highpseudoword list, half of Manelis's word pairs were used in one random order and the other half in the other order. Subjects were randomly assigned to a particular order, with the constraint that the two orderings of each proportion list were presented equally often across subjects. Three types of practice list corresponded to the three types of experimental list. Each practice list was ISO pairs long. The high-proportion word list contained two thirds words and one third pseudowords. The high-proportion pseudoword list contained two thirds pseudowords and one third words. The third practice list contained half words and half pseudowords. No single letters were presented, and no stimuli from the experimental lists appeared during practice. All words and pseudowords were four letters long. Each pair of stimuli differed by one letter (e.g., BAND-LAND). The critical or distinguishing letter appeared in each of the four letter positions equally often. The position of single letters, when they

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

677

Table 1 Mean Single-Letter Positional Frequencies of Occurrence for Words, Pseudowords, and Nonsense Strings Used as Critical Items, Computed From Tables by Mayzner and Tresselt (1965) Letter position pool

1

2

3

4

total"

520.6 488.0 301.1

2,080.1 2,125.8 1,246.5

519.7 495.8 354.2

2,160.2 2,186.0 1,319.6

b

Words Pseudowords Nonsense

Experiments 1 and 2 394.4 347.6 817.5 848.5 390.9 401.4 292.8 243.0 409.6

Words Pseudowords Nonsense

Experiments 3 and 4C 866.8 376.6 397.1 403.7 903.6 382.9 241.0 434.9 289.5

Note, Digram positional frequencies of occurrence were not computed, given McClelland and Johnston's (1977) report that digram frequencies do not predict performance in tachistoscopic recognition. Analyses of variance showed that for both the whole corpus of stimuli and the subset used in Experiments 3 and 4, words and pseudowords were equal in summed total frequency and in distribution of frequencies across letter positions. Words and pseudowords exceeded nonsense strings in summed total frequency, and both differed from nonsense strings in distribution of frequencies across letter positions. b Stimulus pool consisted of 96 strings of each type. c Stimulus pool consisted of 48 strings of each type drawn randomly from the critical items of Experiments 1 and 2. a

occurred, was also varied, appearing equally often at each of the four display positions defined by the words and pseudowords. For each pair of words differing by a particular letter at a particular position, a pair of pseudowords and a pair of single letters differed in the same way (see Table 1). Presented on a Hewlett-Packard cathode-ray-tube oscilloscope and viewed at a distance of 1.22 m, the four-letter stimuli subtended approximately 1.2° of horizontal visual angle. Procedure. First we will describe the trial-bytrial procedure, and then the organization of the experimental session. Each trial block began with the subject seated before the oscilloscope, which displayed the phrase "Press a key when ready," referring to the two response keys arrayed one above the other on the table between the subject and the oscilloscope. Following the subject's key press, a row of four fixation points was presented, indicating where the target stimulus would appear. The fixation points remained in view for 500 msec. The target stimulus was presented immediately following the fixation points and remained in view for a duration determined in the practice trials. On each trial, one member of a stimulus pair was chosen at random to be the target. The stimulus chosen from each pair was counterbalanced across subjects. A patterned mask and two response alternatives then replaced the stimulus. One alternative appeared above the mask and the other below. The alternatives were whole words, whole pseudowords, or single letters, depending on the target stimulus. The mask consisted of Xs and Os superimposed over each of the four letter positions. This display remained in view

until the subject indicated which alternative had been the target stimulus by pressing the appropriate key. Subjects were instructed to take as much time as they wished in order to give the most accurate response they could. Depending on the response, the word "correct" or "error" was displayed for 500 msec. The next trial then began with the presentation of the four fixation points. The experimental session was organized in the following way. At the beginning of the session, subjects received 150 practice trials. The practice session was used to familiarize subjects with the task and to determine the optimal stimulus duration for each subject, which was the exposure time at which the subject was consistently correct on 75% of the trials. To determine this duration, we gave the subject 15 blocks of 10 trials each. The duration for the first 10 trials was 100 msec. Duration was shortened after each block of trials in which the subject was correct on more than eight trials, and it was lengthened after each block in which the subject was correct on fewer than seven. In this way an asymptotic duration producing about 75% correct responding was established. All subjects reached an asymptote within the 150 trials, and all durations were less than 100 msec. Following the practice session, subjects participated in three experimental blocks of trials, corresponding to the three types of stimulus list. The order in which lists were presented was counterbalanced across subjects, and the first block was always similar to the practice list the subject had seen. For example, a subject who had practiced on the high-proportion word list received the high-

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T. CARR, B. DAVIDSON, AND H. HAWKINS

proportion word list for the first experimental block of trials. Prior to each block, subjects were told which type of stimulus would occur most frequently and that we were especially interested in performance on that type. We hoped that this measure would strengthen the effect of manipulating proportion.

Results All analyses were performed on responses to the stimuli taken from Manelis (1974). Filler items, which were less well controlled on structural characteristics across stimulus types, were not included in the analyses.1 First, a 3 X 3 analysis of variance was performed on percentage of correct response data from each subject's first block of trials only. This analysis provided an uncontaminated between-groups estimate of the effects of proportion-induced expectation. Target type (word, pseudoword, single letter) was varied within subjects, and proportion (high word, equal, high pseudoword) was varied between groups. A main effect occurred for target type, F(2, 30) = 6.63, p < .005, MSe = 99.4. NewmanKeuls multiple comparisons showed that performance on words (80.3%) was significantly better (p < .05) than performance on pseudowords (72.8%) and that performance on both kinds of orthographically regular stimuli was significantly better (p < .05 or beyond) than performance on single letters (67.8%). No other significant effects were found in the first-blocks analysis. Both proportion and the interaction between proportion and target type produced F ratios less than 1. Next, a 3 X 3 X 3 analysis of variance was performed on percentage of correct response data from the experiment as a whole. This analysis allowed a withinsubjects estimate of flexibility in response to changing task demands. Target type and proportion were varied within subjects, and order (high word first, equal first, high pseudoword first) was varied between groups. A main effect occurred for target type, F(2, 24) = 10.34, p < .001, MS, = 210.1. Words (78.1%) were identified most accurately, followed by pseudowords (75.1%) and single letters (65.9%). The difference between words and pseudowords

failed to reach significance according to Newman-Keuls multiple comparisons. Both orthographically regular target types were identified significantly more accurately than single letters (p < .05 or beyond). No other effects even approached significance in this analysis, which indicates that the withinsubjects manipulation of proportionality was no more influential than the betweengroups manipulation had been by the previous analysis. Discussion Our attempt to manipulate reliance on lexicality in a situation in which orthographic mechanisms should always be in operation appears to have failed. Despite large variations in the relative probability of seeing words or pseudowords and the accompanying instructions that emphasized the more likely target type, relative performance on words and pseudowords remained fairly constant. Indeed, it is not clear that lexicality influenced performance at all under the conditions of this experiment. The between-subjects analysis indicates a 7.5% initial advantage for words over pseudowords. However, the overall analysis, conducted within subjects, does not provide much support for the superiority of words. These results are amenable to several interpretations. We could assume that lexicality does not contribute in a substantial way to performance in tachistoscopic recognition. If so, then attempts to manipulate reliance on lexicality would of course be doomed to failure. Consistent with this interpretation, frequency of occurrence in the written language (Kucera & Francis, 1967) did not affect performance significantly in Experiment 1. A t test was used to compare correct responding on a 1 Because of the highly nonrandom nature of stimulus selection and counterbalancing procedures, all the analyses reported in this article treated stimuli as a fixed effect. Tests over stimuli would be a valuable contribution to understanding the generality of these phenomena and should be carried out in future research, with appropriately random stimulus selection.

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

set of 16 high-frequency words (median frequency of 217.0 occurrences per million, mean frequency of 405.6) and a set of 16 low-frequency words (median frequency of 2.0, mean frequency of 3.3) selected from the high-proportion word condition. The difference of 4.6% was in the direction of a high-frequency advantage but was highly unreliable, *(17) = 1.06, p > .25. If lexical status does not influence tachistoscopic recognition, then differences between words and pseudowords, when they occur, would have to be attributed to uncontrolled variations in regularity or pronounceability. However, if we assume that the small indications of a lexicality effect are real rather than illusory, two other possibilities are suggested. First, it may be that at least as long as subjects realize that words can occur, lexicality will play its part in perception independently of any more specific expectations the subject may have. That is, the lexical mechanism may be activated to the same degree whenever a word is presented, irrespective of the frequency with which words occur. Alternatively, it may be that lexical access is more specifically controllable but that this flexibility shows up only when orthography is not attended. To put these speculations to a test, one should manipulate expectancy for orthographic structure as well as lexicality, in hopes of removing attention from both of these word properties rather than from lexicality alone. Experiment 2 The purpose of the second experiment was to pursue these two possibilities by using the relative frequency of nonsense strings in a trial block to manipulate reliance on both the orthographic and the lexical mechanisms simultaneously. A set of critical items consisting of equal numbers of words, pseudowords, and nonsense strings was randomly distributed through blocks of trials consisting mainly of either word fillers or nonsense fillers. As in Experiment 1, each trial block contained a few single letters included to provide a baseline level of performance. The result was two stimulus mixtures, one in which the subject

679

should have considerable incentive to attend to both orthography and lexicality and one in which the subject should have incentive to treat the stimuli as collections of independent letters. Each subject received both proportion conditions, which allowed the same between-groups and within-subjects estimates of flexibility obtained in Experiment 1. Method Subjects, Twenty-four volunteers were selected with the same qualifications and paid in the same way as in the first experiment. Materials. Two types of stimulus list were used: (a) high-proportion regular and (b) high-proportion irregular. The high-proportion regular list contained 72 pairs of words (48 filler pairs), 24 pairs of pseudowords, 24 pairs of nonsense strings or orthographically irregular nonwords, and 24 pairs of single letters. Thus two thirds of the stimuli were regular, of which three quarters were words. The high-proportion irregular list contained 72 pairs of nonsense strings (48 filler pairs), 24 pairs of single letters, 24 pairs of pseudowords, and 24 pairs of words. Only one third of the stimuli in this list were orthographically regular, of which one half were words. Two different versions of each kind of list were constructed, each of which was presented to an1 equal number of subjects. One version of each list contained a randomly selected half of Manelis's (1974) words and pseudowords, with the other version containing the other half of Manelis's stimuli. Nonsense strings were constructed by scrambling the letters of each pseudoword to produce strings that were as irregular and unpronounceable as possible while preserving the location of the pair of letters distinguishing each pair of stimuli (see Table 1). One practice list was used in this experiment, half of which was words and pseudowords and half of which was nonsense strings, drawn in random order. Again, there was no overlap between practice and experimental stimuli. Procedure. The procedure for the practice session was the same as in Experiment 1. Following practice each subject received the two kinds of stimulus list as separate trial blocks, with order of administration counterbalanced across subjects. Instructions emphasized either words or nonsense, depending on the stimulus list. Trial-by-trial procedures were the same as in Experiment 1.

Results First, a 4 X 2 analysis of variance was performed on percentage of correct responses from the data from each subject's first block of trials. Target type (word, pseudoword, nonsense string, single letter)

680

T. CARR, B. DAVIDSON, AND H. HAWKINS

was varied within subjects, and proportion (high regular, high irregular) was varied between groups. A main effect occurred for target type, F(3, 66) = 8.03, p < .001, MSa = 108.4. Newman-Keuls multiple comparisons showed that words (76.4%) and pseudowords (76.0%) did not differ and were identified more accurately than nonsense (68.9%). All three of these were identified more accurately than single letters (63.9%; all ps < .05 or beyond). Both the main effect of proportion and the Target Type X Proportion interaction produced /''ratios less than 1. Next, a 4 X 2 X 2 analysis of variance was performed on percentage of correct responses from the experiment as a whole. Target type and proportion were varied within subjects, and order (high regular first, high irregular first) was varied between groups. A main effect was found for target type, F(3, 84) = 12.86, p < .001, MSe = 126.8. Newman-Keuls multiple comparisons showed that words (75.4%) were not identified significantly better than pseudowords (72.7%). Both of these were identified more accurately than nonsense strings (67.8%), and all three multiletter stimuli were identified more accurately than single letters (63.6%; all ps < .05 or beyond). Though the interaction between target type and proportion was far from significance, inspection of the means revealed an apparent trend in the direction predicted by the existence of flexible orthographic processing: The difference between words and pseudowords seemed to be larger in the

high-irregular condition than the highregular condition, and the difference between pseudowords and nonsense strings appeared to be smaller (see Table 2). We pursued the possibility of this interaction by applying both a t test and Wilcoxon's nonparametric sign test to each of two sets of difference scores, one calculated by subtracting performance on pseudowords from performance on words and the other by subtracting performance on nonsense strings from performance on pseudowords in each proportion condition. Despite the greatly inflated chance of a Type I error, none of these tests approached significance (all ps > .25). The bulk of the evidence emerging from Experiments 1 and 2 argues against the reliability of the small differences in performance observed between words and pseudowords. To gain further evidence on this issue, we performed a 3 X 4 analysis of variance on the data for words, pseudowords, and single letters from the four extreme proportion conditions of the first two experiments combined. The equalproportion condition of Experiment 1 was excluded from this post hoc analysis in hopes of increasing power, since that condition was more variable than either the high-word or the high-pseudoword condition. Only first-trial blocks were included, making proportion a between-subjects factor and equating experimental conditions across its levels. The main effect of target type was significant, F(2, 64) = 12.43, p < .01, MSC = 111.00. Newman-Keuls multiple comparisons revealed that words

Table 2 Percentage of Correct Recognition in Experiment 2 as a Function of Target Type, List Proportion, and Order of Presentation of Proportion Conditions Order 1 Target type Word Pseudoword Nonsense Single letter

Order 2

High regular

High irregular

High irregular

74.6 76.0 70.1 63.5

72.9 64.9 68.0 65.3

78.1 76.0 67.7 64.2

High regular 78.1 76.0 70.5 67.0

Note. Order 1 received the high-proportion regular list first followed by the high-proportion irregular list. Order 2 received the high-proportion irregular list first.

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION (77.7%) and pseudowords (75.3%) did not differ significantly but that both were superior to single letters (66.1%). The interaction between target type and proportion produced an F ratio less than 1, as did the main effect of proportion.

681

cited data should be taken to indicate any substantial degree of perceptual flexibility. Experiment 3

Following Experiment 2, then, we were left in a rather uncomfortable position. Discussion First, the perceptual flexibility we thought we would find quite readily proved instead Contrary to the expectations with which to be elusive. Second, the evidence rewe began the study, the orthographic mained entirely ambiguous as to whether mechanism seemed to be in operation and words are identified with any greater to provide a fairly constant advantage to accuracy than pseudowords under these perception independently of the actual conditions. Thus we could not say whether probabilities of occurrence of regular and one or two mechanisms are involved in irregular strings in Experiment 2. Because tachistoscopic recognition, and we certainly the analytic power of the experiment decould not say how the mechanisms are pended on obtaining variation in sensitivity related to one another if two are involved. to orthographic structure, we cannot draw Accordingly, the third experiment was any firm conclusions about the organization designed to impose a more extreme manipuof the word-processing system. However, lation upon the expectations of our subjects. the outcome of Experiment 2 does force us Three procedural changes were made relato reconsider the role of strategic control tive to Experiments 1 and 2. First, subjects in word recognition. were exposed during practice only to irOur difficulty in producing flexibility regular nonsense strings in order to establish seems to be at odds with Aderman and similar ranges of exposure durations across Smith's (1971) report that differential experimental conditions. Second, once reliance on structural analysis can be practice was completed, an absolute exdemonstrated with relatively modest pectation for stimuli of a single kind was manipulation of subjects' expectations for induced by appropriate instructions. Subpseudowords or nonsense strings. This jects in one group were told they would manipulation consisted of 15 context trials receive a series of trials consisting entirely followed by one unexpected stimulus. A of nonsense strings in order to provide closer inspection of Aderman and Smith's baseline data for another experiment. In a results, however, suggests that this dissecond group subjects were told they would crepancy may be more apparent than real. receive a series of trials consisting entirely In their experiment, t tests were used to of words in order to determine how well assess the difference in performance bepeople can perceive words at exposure tween pseudowords and nonsense. When durations producing a particular level of pseudowords were expected, the difference performance on nonsense strings. The first in favor of pseudowords was significant. three quarters of the experimental trials When nonsense was expected, the difference conformed to this induced expectancy. Un—though in the same direction—was not expected stimuli were introduced only in significant. This is the critical finding on the final quarter of the experimental trials, which Aderman and Smith built their randomly mixed with expected stimuli. argument for flexibility. However, the Finally, single-letter response alternatives overall analysis of variance revealed a main were substituted for the whole-stimulus effect of target type, a main effect of expectancy condition, and no interaction alternatives of the first two experiments. between them. Since one might ordinarily This was done to eliminate the possibility follow the outcome of the analysis of that subjects could somehow make quick variance in such a situation, it is not clear adjustments based on information gained that even Aderman and Smith's widely at the presentation of unexpected response

682

T. CARR, B. DAVIDSON, AND H. HAWKINS

alternatives, thereby overriding the effects of an established strategy. We assumed that these procedures would be sufficient to manipulate expectations in a substantial way. If so, then finding the same pattern of results as occurred in the first two experiments would imply that the mechanism or mechanisms of word processing used in tachistoscopic recognition are in fact not subject to strategic control. Changes in this pattern of results, however, would first demonstrate that control is possible, at least under extreme expectation conditions. Second, the nature of the change could shed some light on the kind of mechanism or mechanisms involved. Most enlightening would be a dissociation between performance on words and performance on pseudowords in response to a particular expectation, since this would clearly indicate that two mechanisms are involved and that they can be independently manipulated. Method Subjects. Seventy-one volunteers were selected as in Experiments 1 and 2 and were paid $2.50 for participating in the 30-minute session. Materials. Four stimulus lists were created for each expectation condition. The first 72 stimulus pairs in each list were all of the same type, either nonsense strings or words. These items could occur in one of two random orders randomly assigned to subjects. For nonsense expectation, the remaining 24 pairs in each list were a mixture of nonsense strings and either words or pseudowords. Order of occurrence of these 24 "critical items" was randomized separately for each individual stimulus list. The critical items for this experiment were drawn from a pool of 24 pairs of word stimuli and their corresponding pseudoword and nonsense stimuli chosen at random from the 48 pairs of each type used as targets in Experiment 2. Two lists with unexpected words were made up by combining 12 of the nonsense pairs with 12 of the word pairs and the remaining 12 nonsense pairs with the remaining 12 word pairs. Two lists with unexpected pseudowords were constructed by replacing the word pairs with pseudoword pairs. Lists for the word expectation condition were constructed by replacing the 72 pairs of context nonsense strings with words. This method of list construction made it possible to obtain an overall performance measure for the 72 context trials as well as measures of performance on expected and unexpected critical items as a function of position of occurrence: first unexpected item, second unexpected item, and so on.

Subjects in both expectation conditions recc'ived only nonsense strings as practice stimuli. Singleletter response alternatives rather than wholestimulus alternatives were used for all stimuli to keep subjects from noticing, because of the response alternatives, that unexpected stimulus types were sometimes being presented. Procedure. Following the practice session each subject received one block of experimental trials. If the subject was induced to expect nonsense, these trials consisted of one of the two versions of either the list containing unexpected words or the list containing unexpected pseudowords. If the subject was induced to expect words, the experimental trials consisted of one of the two versions of either the list containing unexpected pseudowords or the list containing unexpected nonsense. Other than the changes described above, all procedures were the same as in Experiments 1 and 2.

Results Separate 2 X 4 X 3 X 2 analyses of variance were performed for the nonsense expectation and word expectation conditions, from the percentage of correct response data from each subject's last 24 trials (see Table 3). Data from seven subjects in the nonsense expectation group were discarded for failing to perform significantly above chance (which was 59.7% or better) during the 72 context trials. We felt this was necessary in order to assure that subjects were actually getting some usable information from the target display and carrying on with the task at a reasonable level of success and motivation. In each analysis, type of trial (expected target, unexpected target), trial block (first, second, third, fourth group of three critical trials), and serial position (first, second, third trial within a trial block) were varied within subjects. Trial block and serial position were included in order to obtain a more sensitive measure of changing levels of performance on expected and unexpected targets during the course of the critical trials than would be provided by a single serial position factor with 12 levels. Unexpected target type (word or pseudoword for nonsense expectation and pseudoword or nonsense for word expectation) was varied between groups. When nonsense was expected, main effects were found for type of trial, F(\, 30) = 5.69, p < .05, MSe = 1,665.80, and for

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

683

Table 3 Percentage of Correct Recognition in Experiment 3 as a Function of Expectation and Type of Trial Nonsense expectation trial Unexpected Group 1 2

Expected nonsense

Word

69.3 68.6

85.4

Pseudoword 66.7

Word expectation trial Unexpected Expected word

Nonsense

84.9 84.4

69.8

unexpected target type, F ( l , 30) = 6.86, p < .05, MSe = 2,596.40. The interaction between these two variables was also significant, F(l, 30) = 9.57, p < .01, MS, = 1,665.80, reflecting the fact that unexpected words (85.4%) were identified considerably more accurately than expected nonsense (69.3%) but that unexpected pseudowords (66.7%) did not differ at all from expected nonsense (68.6%). Subjects in this condition were asked at the end of their sessions whether they had noticed any changes in the stimuli they were seeing during the course of the experiment. Those who received unexpected pseudowords were uniform in saying they had not, and they expressed surprise when told about the occurrence of the orthographically regular strings. Subjects who received unexpected words were mixed, 3 reporting they had not noticed words and 13 reporting that they had. Those who said they had noticed words were asked whether the realization was abrupt or had developed over trials. Again, reports were mixed. For the group of subjects as a whole, however, there was no apparent relation between reports about awareness of unexpected words and recognition performance. When words were expected, the only significant effect was the main effect of type of trial, F(\, 30) = 16.23, £ < .005, MSe = 2,085.60, in which expected words

Pseudoword 72.9

(84.6%) were identified more accurately than either of the unexpected stimulus types (71.4%). The interaction between type of trial and unexpected target type produced an F ratio less than 1. Unexpected pseudowords were identified with 72.9% accuracy compared with 84.4% accuracy on expected words. Unexpected nonsense strings were identified with 69.8% accuracy compared with 84.9% on expected words. Subjects in this condition uniformly reported not noticing that pseudowords or nonsense strings were occasionally being presented. In addition, a combined 2 X 4 X 3 X 2 analysis of variance was performed on percentage of correct critical trial data from the group of subjects that expected nonsense and were surprised with words and from the group that expected words and were surprised with nonsense, directly comparing relative performance on words and nonsense as a function of opposing expectations. Target type (word, nonsense), trial block (1-4), and serial position (1-3) were varied within subjects, and expectation (word, nonsense) was varied between groups. A main effect was found for target type, F(l, 30) = 28.27, p < .001, MSK = 1,658.0, in which words (85.2%) were recognized more accurately than nonsense (69.5%). Both the main effect of expectation and the interaction between expecta-

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tion and target type produced F ratios less than 1. Finally, a between-groups comparison of pseudoword recognition under nonsense expectation and word expectation was carried out. Though mean recognition accuracy for pseudowords was higher when words were expected (72.9%) than when nonsense was expected (66.7%), the difference was not at all reliable, F(\, 30) < 1.00. Discussion These results are quite surprising, given the patterns of recognition performance observed in Experiments 1 and 2. First, it appears that expectancy had absolutely no effect on the ability to recognize either nonsense strings or words. Accuracies on words and nonsense were identical in the two expectation conditions. While this outcome is consistent with the notion that lexical access is automatic rather than controllable (cf. Fischler, 1977), the accompanying' failure to find evidence for the operation of any kind of orthographic mechanism, either automatic or strategic, is inconsistent with all current conceptions of word processing. There are two possible explanations for the decrement in identification accuracy on pseudowords relative to the previous experiments. First, alteration of response alternatives from whole strings to single letters may differentially interfere with the processing of pseudowords. Though it is a bit difficult to imagine why this should occur, Manelis (1974) did find that the difference between words and pseudowords was somewhat larger with single-letter response alternatives than with wholestring alternatives. Since Manelis did not include nonsense strings or single letters, there is no baseline against which to evaluate this increase in the word-pseudoword difference. The second possibility is that an assumption made implicitly in most wordprocessing models is incorrect. So far we have supposed that because an orthographic mechanism can be applied to the processing of words, it will be applied. How-

ever, it is conceivable that orthographic computation is invoked only when there is reason to believe it might be needed. For words, which already have unified memorial representations at various levels of analysis, such computation may not be required. For pseudowords, some kind of computation would be the only way to achieve a higher order code such as a pronunciation capable of surviving visual masking and unifying single-letter information into a more compact or efficient representational form. 2 Since subjects in Experiments 1 and 2 knew that pseudowords would sometimes occur, but subjects in Experiment 3 were unaware that pseudowords would ever occur, this hypothesis is consistent with all the results so far. If Coltheart (in press) is correct in arguing that lexical access through the visual system is usually faster than orthographic computation as a means of activating an internal representation of a word, then this kind of organization of the wordprocessing apparatus might be plausible as well as possible. Therefore Experiment 4 was designed to investigate the hypothesis that an expectation for pseudowords is necessary in order for tachistoscopic recognition to benefit from their structural regularity. 2 We should point out that the conditions of these experiments are exactly those under which people appear to rely primarily on name codes—whether directly activated for familiar stimuli or computed for unfamiliar stimuli—to support their recognition decisions (Hawkins et al., 1976). Therefore "orthographic computation" should probably refer more specifically to spelling-to-sound translation in this context, as mentioned in the introduction. We feel the present findings are essentially moot with respect to investigations of the role that orthographic structure might play in visual code formation (e.g., Carr, Posner, Pollatsek, & Snyder, in press; Pollatsek & Carr, Note 2). We might note, however, that visual word advantages found in same-different matching, which are probably attributable almost entirely to orthographic regularity (Pollatsek & Carr, Note 2), are subject to manipulation via expectations, at least under certain conditions (Schindler, Well, & Pollatsek, 1974). Whether this effect should be characterized as facilitation for expected regular strings (Schindler et al., 1974) or as inhibition for unexpected nonsense (LaBerge et al., 1977) is not yet clear.

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

Experiment 4 Method Subjects. Subjects were 40 volunteers recruited from two undergraduate psychology courses. Qualifications were the same as in the first three experiments. In addition to receiving $2.50 for participating in the 30-minute session, some subjects received laboratory credit from their instructor. Materials. Four stimulus lists were created by using the same format as in Experiment 3. In these lists, context trials consisted of 72 pairs of pseudowords. Critical trials consisted of 12 pairs of pseudowords and 12 pairs of either words or nonsense strings. Two different random orders of the context trials were used, randomly assigned to subjects. Critical items were the same stimuli used in Experiment 3, except in this experiment pseudowords were the expected targets and words or nonsense the unexpected targets. Procedure. All experimental procedures were the same as in Experiment 3. Subjects were told that after practicing on nonsense strings, they would receive a series of trials consisting entirely of pseudowords in order to determine whether spelling patterns and pronounceability affect perception at exposure durations producing a particular level of performance on nonsense strings.

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Table 4 Percentage of Correct Recognition in Experiment 4 as a Function of Type of Trial and Unexpected Target Type Pseudoword expectation trial Unexpected Group 1 2

Expected pseudoword

Word

74.5 74.0

78.6

Nonsense 63.5

5.00, p < .05, MSe = 2,083.3. In addition, a main effect was found for unexpected target type, ^(1, 30) = 4.91, p < .05, MSe = 2,385.5, which cannot be interpreted without reference to the interaction. It should be noted that although overall levels of performance were lower in this experiment than in Experiment 3, the difference between words and nonsense was identical at 15.1%.

Results

Discussion

A 2 X 4 X 3 X 2 analysis of variance was performed on percentage of correct response data from each subject's last 24 trials (see Table 4). Data from eight subjects were discarded, four for failing to achieve exposure durations under 100 msec and four for failing to perform significantly above chance during the 72 context trials. Type of trial (expected target, unexpected target), trial block (first, second, third, fourth group of three critical trials), and serial position (first, second, third trial within a trial block) were varied within subjects. Unexpected target type (word, nonsense) was varied between groups. The major result of this analysis was an interaction between unexpected target type and type of trial, F(i, 30) = 4.24, p < .05, MSe = 2,402.8. Simple effects analyses showed that performance on expected pseudowords (74.5%) and unexpected words (78.6%) did not differ significantly, F(l, 15) < 1.00 whereas performance on expected pseudowords (74.0%) was significantly better than performance on unexpected nonsense (63.5%), F(l, 15) =

Clearly the hypothesis that expectations affect the ability to recognize pseudowords under demanding perceptual conditions was supported. Taken together, the results of Experiments 3 and 4, summarized in Table 5, indicate that performance on words and nonsense was not influenced by expectations. This implies that memorial representations of both words and letters are automatically activated, at least as long as the usual spatial configuration of letter strings is not disrupted (see Schindler et al., 1974; Purcell, Stanovich, & Spector, Note 3). However, perceiving a pseudoword as something more than a string of independent letters under conditions of tachistoscopic presentation appears to require knowledge of the possibility that pseudowords can occur. To avoid any misleading comparisons across separate analyses in drawing this conclusion, we subjected data from Experiments 3 and 4, collapsed across trial block and serial position, to a combined 2 X 6 analysis of variance. Target type (expected, unexpected) was varied within subjects

T. CARR, B. DAVIDSON, AND H. HAWKINS

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Table 5 Percentage of Correct Recognition in Experiments 3 and 4 Combined as a Function of Expectation and Target Type Expectation Target Word Pseudoword Nonsense

Word

Pseudoword

Nonsense

84.6 72.9 69.8

78.6 74.2 63.5

85.4 66.7 69.0

and expectation condition was varied between groups. The six levels of expectation condition were (a) expected nonsense/unexpected words, (b) expected nonsense/ unexpected pseudowords, (c) expected words/unexpected pseudowords, (d) expected words/unexpected nonsense, (e) expected pseudowords/unexpected words, and (f) expected pseudowords/unexpected nonsense. The interaction between target type and expectation condition was highly significant in this analysis, F(5, 90) = 6.46, p < .001, MSe = 1,711.3. Simple effects analyses with the Newman-Kuels procedure showed the same pattern of differences reported in the results of the individual experiments. In particular, the difference of 10.5% in favor of pseudowords in the expected pseudoword/unexpected nonsense condition was significant (p < .05), and the difference of 2.0% in the expected nonsense/unexpected pseudoword condition was not. Thus, utilizing orthographic structure in the computation of internal codes that will survive masking and support recognition performance is not automatic but is under some degree of strategic control. General Discussion We began these experiments with two goals in mind. The first was to gain some insight into the organization of orthographic and lexical mechanisms involved in the perception of words. The second, necessary to achieve the first, was a more thorough understanding of the nature of strategic flexibility in the operation of these mechanisms. On the basis of work by

Neisser (1967, 1976), Aderman and Smith (1971), James (1975), and Shulman and Davison (1977), we had taken for granted the existence of a facile system of word perception. From this we were led to the hypothesis that the empirical contradiction between Baron and Thurston (1973) and Manelis (1974) could be attributed to differences across studies in the relative proportions of words, pseudowords, and nonsense strings presented as stimulus material. In the end, our results shed little light on the particular disparity between these two studies. This is because we cannot say for certain whether words were ever identified more accurately than pseudowords in our first two experiments conducted within the range of stimulus conditions imposed by Baron and Thurston and by Manelis. However, the results do illuminate the issue of strategic flexibility in several more general ways. First, it is clear from Experiments 1 and 2 that the mechanisms of word perception are not nearly so facile as we had initially believed. We were able to obtain evidence for strategic flexibility under none but the most extreme of expectations. Further, these expectations affected only performance on pseudowords, neither impairing nor enhancing the ability to recognize words. Given the intuitive appeal of the notion of attended adaptation to changing task demands, this is in some ways a regrettable outcome. On the other hand, it seems important to discover that the perceptual capacities of people who spend a great deal of time reading have become so highly specialized for the job. From the results of Experiments 3 and 4, we can also draw some conclusions about the organization of these mechanisms that seem so well adapted to reading. The dissociation between performance on unexpected words and unexpected pseudowords found in Experiment 3 is consistent with a class of models in which lexical information enjoys automatic access to central processing regardless of the perceiver's expectations but orthographic information requires the attended utilization of some computational process. We cannot tell from the data whether attention determines

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

the occurrence of the computation or the transfer of its output to decision mechanisms. Thus it may be that higher order codes for pseudowords are not constructed and therefore are not available unless people expect to need them, or it may be that higher order codes actually do become available for pseudowords but go unaccessed during decision processes unless people expect to need them. In either case, the results of Experiments 3 and 4 show that lexical and orthographic analyses constitute isolable subsystems of the word perception apparatus and that these subsystems differ markedly in their susceptibility to cognitive control. There is, however, an alternative interpretation which would lead to a very different conception of the role of expectations in word perception were it correct. Suppose that all encoding processes, both lexical and orthographic, occur automatically when a string of letters is presented and that all resulting codes are in fact transferred to decision mechanisms. Now consider what might happen when the perceiver expects to see a word but receives a pseudoword instead, for example, MARD. Realizing MARD is not a word, the perceiver assumes that under these demanding conditions in which the stimulus is almost never seen with complete clarity anyway, he or she has simply misread the string. The recognition decision is then changed to the nearest word that comes to mind, perhaps MARK or HARD. When the response alternatives occur, the perceiver is faced with M versus D (for MARD or DARD). If the stimulus had been identified as HARD, a random guess would have to be made, increasing the likelihood of an error. If the perceiver had been luckier and changed the stimulus to MARK, the correct choice would be made even though the stimulus was incorrectly identified. Combining these two kinds of mistaken strategic perturbations of already-recognized, stimulus information in a block of trials, performance on pseudowords would be worse when words are

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expected exclusively than when pseudowords are known to be a possibility.3 However, although this conscious perturbation model can quite parsimoniously explain a drop in accuracy on pseudowords under word expectations, it cannot readily accommodate as large a drop relative to accuracy on nonsense strings as occurred in our data. Each pseudoword conformed to the spelling patterns of English and in fact differed from a real word at only one letter position. Each nonsense string, on the other hand, was made to be as unlike any English word as possible. Therefore perturbing pseudowords into words would on the average require fewer letter changes than perturbing nonsense strings into words. Thus pseudowords perturbed into words would on the average preserve more letters from the originally presented stimulus than would nonsense strings perturbed into words. This means that pseudowords should always have been identified more accurately than nonsense under word expectations, even if they were no longer identified as well as words. We did not find this to be the case. It seems that the conscious perturbation model has even more trouble with the pattern of results obtained under absolute expectations for nonsense strings. First, the assumption must be made that when nonsense is expected, a perturbation in the direction of nonsense is applied only to pseudowords and never to words, since accuracy on words under nonsense expectations did not differ from accuracy on words under word expectations (see Table 2 and the analyses of data from Experiment 3). However, the tendency to read letter strings as words may be a very deeply ingrained habit. Perhaps one could assume that under nonsense expectations, stimuli will be perturbed into nonsense unless they seem particularly wordlike, in which case they will be identified as words. Now undiminished performance on words can be explained, but the perturbation model must face the same objection raised under word expectations. Since pseudowords are more 3 We wish to thank Michael Posner for raising the possibility of this interpretation.

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T. CARR, B. DAVIDSON, AND H. HAWKINS

similar to words than to nonsense, at least some of them should be identified as a similar word instead of a nonsense string. Because fewer changes will be made on those pseudowords identified as words, accuracy on those stimuli should not suffer as badly as accuracy on those identified as nonsense. Therefore the perturbation model again predicts that accuracy on pseudowords should be better than accuracy on nonsense. This was even less the case under nonsense expectation than under word expectation. We must assume for the present, then, that our data reflect some process that prevents higher order codes for pseudowords from reaching decision mechanisms rather than a conscious perturbation applied to such codes after they have been accessed. Therefore, the idea of two independent encoding mechanisms, one automatically utilized and one used only when needed, is the most attractive interpretation of our data. The notion that access to lexical or semantic memory and access to orthographic computation go on in parallel is consistent with most of the existing data from word-processing tasks in which words and pseudowords are mixed together or in which responses must be based on how words sound as well as how they are spelled (Baron & Strawson, 1976; Coltheart, in press; Meyer & Gutschera, Note 4). Models of word processing derived from these data have found it necessary to suppose that contact with meaning is a "horse race" between a visual code representing stimulus information rather directly and a phonetic or name code computed from visual input by the application of spelling-to-sound translation rules. Thus it is assumed that direct visual access to the lexicon occurs in parallel with an orthographic computation that produces phonetic access to the lexicon. The horse-race models predict performance quite well for tasks in which people know that pseudowords can sometimes occur. However, it appears from Experiment 3 that when people strongly expect to see nothing but words, pseudowords are no longer treated as regular and pronounceable but are treated like irregular nonsense strings. If one assumes that during ordinary

reading, people in fact entertain absolute expectations for familiar words, then our finding would seem to impeach the horserace notion as a general model of the word recognition processes involved in reading. Instead, direct access to a stimulus-specific mechanism in the absence of concurrent reliance on spelling-to-sound computation may be the "preferred" mode of operation for the word perception apparatus. Barron and Baron (1977) demonstrated that such a direct access route becomes available quite early in the development of reading skills. In their experiment, it was found that a secondary task, such as saying "double" over and over, interfered with first graders' ability to make rhyming decisions about pairs of familiar words but not with their ability to judge whether the words were semantically related. This indicates that access to stimulus-specific semantic information can occur without phonetic mediation, even in children just completing their first year of formal reading instruction. If direct visual access to the lexicon does develop so early, what purpose could be served by an independent flexible mechanism of orthographic computation? As a route to meaning, this mechanism may be substantially less efficient than visual access (Coltheart, in press), and the information about spelling-to-sound translation embodied in the mechanism is certainly difficult to learn (Rozin & Gleitman, 1977). It must be, then, that orthographic computation is not completely redundant with visual access but performs some important function of its own. Although it is true that poor readers usually have smaller vocabularies than good readers, Perfetti and Hogaboam (1975) reported that the time taken to name a pseudoword distinguishes much better between good and poor readers than the time taken to name a word with which both groups are familiar. These two facts together suggest that perhaps the reason why poor readers have smaller reading vocabularies is their apparent difficulty in using the spelling-to-sound translation rules of the language. On this view, the orthographic mechanism may exist as a means of turning print into

PERCEPTUAL FLEXIBILITY IN WORD RECOGNITION

speech, allowing words not yet in the reader's visually accessible lexicon to contact his or her sometimes larger and almost always different speaking lexicon (see Szumski & Brooks, Note 5). Orthographic computation, then, could serve as a vocabulary builder for the reading process. While this may not be the only interpretation that could be given to these data, it is an interesting one deserving further exploration. Reference Notes 1. Morton, J. Some experiments on facilitation in word and picture recognition and their relevance for the evolution ofti theoretical position. Paper presented at the conference on "Processing Visible Language," Institute for Perception Research, Eindhoven, The Netherlands, September 1977. 2. Pollatsek, A. & Carr, T. H. Rule-governed and wholistic encoding processes in word perception. Paper presented at the conference on "Processing Visible Language," Institute for Perception Research, Eindhoven, The Netherlands, September 1977. 3. Purcell, D. G., Stanovich, K., & Spector, A. Control processes, structural features, and the word superiority effect. Paper presented at the meeting of the Psychonomic Society, Washington, D.C., November 1977. 4. Meyer, D. E., & Gutschera, K. D. Orthographic versus phonemic processing of printed -words. Paper presented at the meeting of the Psychonomic Society, Denver, Colorado, November 1975. 5. Szumski, J., & Brooks, L. R. Word-specific learning in rapid word identification. Manuscript submitted for publication, 1977.

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