Differential backward masking of words and letters by masks of varying orthographic structure

The effects of structural relationships between targets and masks were investigated using a backward-masking paradigm. Specifically, the masking of single letters, common fiveletter words, and five-letter pseudowords masked by a blank flash, strings of overlapped letters, pseudowords, and words was investigated. Target duration was varied from 2 to 32 msec, with mask duration held constant at 25 msec. The dependent measure was the critical interstimulus interval for correct target identification. Letters were more effectively masked than words and pseudowords. A blank mask caused the least amount of masking, followed by the overlapped letter strings, and then the word and pseudoword masks. In addition to the overall greater masking effectiveness for the three patterned masks, overlapped letter strings masked letters more effectively than they did words. The implications of current theories of masking for these results and the implications of these results for theories of word recognition were discussed.     

Word recognition with forced serial processing: Effects of segment size and temporal order variation

Serial processing was forced by displaying words one letter or letter cluster at a time. Letters or clusters appeared in adjacent spatial positions and in rapid sequence, followed immediately by a mask. Under these conditions, there was a sharp increase in the percentage of words correctly identified as the size of the letter clusters presented in series increased. In a control condition without masking, designed to permit parallel processing across clusters, words were identified near-perfectly, regardless of the size of the clusters displayed. Words displayed one letter at a time without masking were identified fairly well even when letters were presented in random order. The results are interpreted as evidence that skilled readers tend to process letters within words in parallel.     

The role of lateral masking and orthographic structure in letter and word recognition.

The present experiments evaluated the contribution of orthographic structure and lateral masking in the perception of letter, word, and nonword test displays. Performance was tested in a backward recognition masking experiment in which a masking stimulus followed the test display after a variable blank interstimulus interval. In agreement with previous findings across different experiments, words were recognized better than single letterd at short interstimulus intervals, but the opposite was the case at long intervals. Performance on the nonwords resembled performance on letters at short masking intervals and performance on words at long masking intervals. The quantitative results were described by a processing model that incorporates the effects of lateral masking and orthographic structure in the dynamic processing of letter strings. Lateral masking tends to lower the potential perceptibility of letters whereas orthographic structure can reduce the uncertainty of the candidate letters in the letter sequence. The present model predicts that the quantitative contribution of each of these processes to performance is critically dependent upon the processing time available before the onset of the masking stimulus.     

Whole-word units are used before orthographic knowledge in perceptual development

A visual search task for target letters in multiletter displays was used to investigate information-processing differences between college students and presecond-grade children (mean age = 7 years, 4 months). The stimulus displays consisted of single words, pronounceable pseudowords, and unpronounceable nonwords varying in length from three to five letters. The mean response times for indicating whether or not a target letter occurred in the display increased with the number of display letters for both groups, although there were apparent differences between groups in the rate of search and type of search strategy used. Pre-second-grade children responded faster to word displays than to pseudoword and nonword displays, indicating that familiar letter strings could be processed faster than unfamiliar strings regardless of whether or not the latter were consistent with rules of English orthography. In contrast, college students processed words and pseudowords about equally well, and both resulted in faster responses than nonwords. As reading skills develop, children apparently come to process familiar words differently from other letter strings. Only after a significant sightword vocabulary is established do children seem to recognize the regularities of standard English orthography and make use of this knowledge to facilitate perceptual processes.     

Forced serial processing of words and letter strings: A reexamination

Words and nonword strings, three and seven letters long, were displayed serially (i.e., one letter at a time) or simultaneously, with or without a backward mask following display of each letter or string. Recognition of words, and of individual letters within words, was markedly impaired in the masked serial condition relative to the unmasked serial, unmasked simultaneous, and masked simultaneous conditions. Analogous differences were smaller or nonexistent for seven-letter nonwords; however, three-letter nonwords produced relatively “wordlike” data. Implications for the issue of spatially serial vs. parallel processing in word recognition are discussed.     

Familiarity affects visual processing of words.

While previous research has demonstrated that words can be processed more rapidly and/or more accurately than random strings of letters, it has not been convincingly demonstrated that the superior processing of words is a visual effect. In the present experiment, the cases of letters were manipulated in letter strings that were to be compared on the basis of physical identity. Mean response time was shorter for words than for nonwords even for pairs of letter strings that differed only in case (e.g., site-site). This finding implies that the advantage of words over nonwords (the familiarity effect) typically observed in the simultaneous matching task is not due solely to comparison of either the word names or the letter names and, thus, that at least part of the familiarity effect must be due to more rapid formation and/or comparison of visual representations of the two letter strings when they are words. Further analysis failed to reveal a significant involvement of phonemic or lexical codes in the comparison judgments.     

Target position and practice in the identification of letters in varying contexts: A word superiority effect

A forced-choice detection paradigm controlling for postperceptual inference was used to investigate letter identification in three-position displays. Letters from a predesignated set of four targets appeared singly, in strings of noise characters, in unpronounceable nonsense strings, and in words. Subjects knew which context would occur, but did not know which of the three display positions would contain the target. Correct detection data were collected at constant exposure duration over five testing sessions. Overall identification accuracy was higher in words than in all other contexts, the first word superiority effect to be found with targets specified in advance since Reicher’s (1969). This effect remained constant over sessions. An interaction between context type and target position showed enhanced accuracy for initial and terminal letters in words, but depressed accuracy at initial and terminal positions in other contexts. This was interpreted to mean that prior knowledge of context is used to alter the dynamics of perceptual analysis.     

Are all letters really processed equally and in parallel? Further evidence of a robust first letter advantage

This present study examined accuracy and response latency of letter processing as a function of position within a horizontal array. In a series of 4 Experiments, target-strings were briefly (33 ms for Experiments 1 to 3, 83 ms for Experiment 4) displayed and both forward and backward masked. Participants then made a two alternative forced choice. The two alternative responses differed just in one element of the string, and position of mismatch was systematically manipulated. In Experiment 1, words of different lengths (from 3 to 6 letters) were presented in separate blocks. Across different lengths, there was a robust advantage in performance when the alternative response was different for the letter occurring at the first position, compared to when the difference occurred at any other position. Experiment 2 replicated this finding with the same materials used in Experiment 1, but with words of different lengths randomly intermixed within blocks. Experiment 3 provided evidence of the first position advantage with legal nonwords and strings of consonants, but did not provide any first position advantage for non-alphabetic symbols. The lack of a first position advantage for symbols was replicated in Experiment 4, where target-strings were displayed for a longer duration (83 ms). Taken together these results suggest that the first position advantage is a phenomenon that occurs specifically and selectively for letters, independent of lexical constraints. We argue that the results are consistent with models that assume a processing advantage for coding letters in the first position, and are inconsistent with the commonly held assumption in visual word recognition models that letters are equally processed in parallel independent of letter position.     

Searching for a pre-specified target letter in briefly displayed words and unpronounceable non-words

Two experiments were designed in which subjects searched briefly displayed and masked arrays of letters for a single pre-specified target. The target was randomly located at one of twelve positions, its identity remained constant throughout, and it was embedded either in the context of words or in a context of unpronounceable strings of letters. In experiment 1 the letters were arranged in two six-item rows, and word and non-waord displays were mixed and presented to a single group of subjects. Accuracy of search was superior when the letters formed words, both for responses scored for correct position and for responses scored for correct row. In experiment 2 word and non-word displays were presented to different groups of subjects, and for both groups the twelve characters were either arranged as before in two rows or were positioned at loci representing the clock positions. Accuracy of search was again superior when the letters formed words and were arranged in rows, but there was no advantage for words when the letters formed a circle. These findings, firstly, indicated that the “word-superiority effect” obtained in experiment 1 was not a result of subjects adopting a word processing strategy for all stimuli, and secondly, they suggested that the word information could not be used to advantage in the absence of spatial cues delineating the words and/or when the letters were not positioned in the usual horizontal arrangement. It was concluded that the results of both studies were consistent with a perceptual account of the word superiority effect.     

Positional uncertainty in lateral masking and the perceptual superiority of words

The possible role of positional uncertainty as a basis for lateral masking and the perceptual superiority of words was examined. The stimuli were five-letter strings, of which the middle three letters were the targets and the end letters were distracting flankers which were positioned either adjacent to the target or separated from it. The trigram targets were of three types (words, pseudowords, and nonwords). The positional uncertainty of individual letters was varied through the use of two response modes, with 18 college students participating in each mode. One group used a response mode which did not allow transpositions of letter sequence, while the other group had no such restriction. The results showed that positional uncertainty affected the magnitude of lateral masking but not that of the word superiority effect, suggesting that different processes underlie these two phenomena. Error analyses within response mode as well as response bias comparisons further confirmed this conclusion.     

Effects of increased letter spacing on word identification and eye guidance during reading

The effect of increasing the space between the letters in words on eye movements during reading was investigated under various word-spacing conditions. Participants read sentences that included a high- or low-frequency target word, letters were displayed normally or with an additional space between adjacent letters, and one, two, or three spaces were present between each word. The spacing manipulations were found to modulate the effect of word frequency on the number and duration of fixations on target words, indicating, more specifically, that letter spacing affected actual word identification under various word-spacing conditions. In addition, whereas initial fixations landed at the preferred viewing position (i.e., to the left of a word’s center) for sentences presented normally, landing positions were nearer the beginnings of words when letter spacing was increased, and even nearer the beginnings of words when word boundary information was lacking. Findings are discussed in terms of the influence of textual spacing on eye movement control.     

The role of familiar units in perception of words and nonwords

This paper investigates the effects of familiarity with whole-word units and letter-cluster units in perceptual encoding of letter strings. Subjects viewed brief, masked presentations of words and pronounceable pseudowords differing in letter cluster frequency. Identification of both display types was compared to control single letters. Perceptual accuracy was indexed by probe forced-choice responses and full verbal reports of the displays. Evidence that familiarity of whole-word units facilitated encoding was mixed but, on balance, favorable. Evidence that familiarity of letter-cluster units facilitated encoding was completely absent. This negative finding is surprising in view of the fact that we did obtain a large advantage of letters in pseudo-words as well as words over single letters. The discussion section considers an alternative to the view that perceivers use detectors for familiar letter-cluster units in the process of forming representations of pronounceable, orthographically regular letter strings.     

A test of the Sophisticated Guessing Theory of word perception

Under difficult viewing conditions, a letter in a familiar word can be perceived more accurately than the same letter alone or in a string of unrelated letters. Sophisticated Guessing Theory asserts that perception is more accurate when a letter appears in a word because its identity is constrained by the identity of neighboring context letters. Experiment 1 tested the following prediction: A letter in a word should be perceived more accurately in strongly constraining word contexts than in weakly constraining word contexts. No such trend was found using a number of different measures of contextual constraint and perceptual accuracy. Experiment 2 verified that, with the same conditions used in Experiment 1 to test Sophisticated Guessing Theory, a strong perceptual advantage could be obtained for letters in words vs. letters alone or in unrelated-letter strings. Several alternative theories of word perception are discussed. The most attractive asserts that for words an additional higher-level perceptual code is formed that is more resistant to degradation than the code formed for letters.     

The interfering effect of word perception on letter identification

Subjects identified a single lowercase letter in a visual display by pressing one of two buttons. Two letters were assigned to each response. Groups received one of three context conditions: word, nonword, or single-letter displays. In words and nonwords, the flanking letters adjacent to the target varied as to whether they were response compatible or incompatible with the target. Single letters produced faster response latencies than either multi-letter condition, and words yielded slower latencies than did nonwords. Items Containing an incompatible-response flanking letter produced longer latencies than items containing a compatible flanking letter. Subgroups of subjects with different characteristic processing patterns were identified with a separate test. These subgroups were differentially affected by the context conditions in the letter-identification task. A greater subgroup difference was found in nonwords than in words.     

Letter identification in relation to linguistic context and masking conditions

With a two-choice detection procedure, identifiability of signal letters was determined in backgrounds of words, nonword letter strings, or homogeneous noise characters. Under high performance conditions of exposure duration and pre- and postmasks, there was a substantial advantage in identifiability of letters presented alone over letters embedded in words; under low performance conditions there were generally no differences between the two types of context, but some interactive effects appeared involving particular letters with serial position and type of background. No differences were obtained between word and nonword contexts. The disparities between these findings and those reported by Reicher (1969) and Wheeler (1970) may be related to the more complete elimination under the present procedures of effects of redundancy on response selection.     

Processing order in visual perception

Initial increases in the availability of items for report following tachistoscopic presentation of centrally-fixated rows of seven random letters were directly evaluated by measuring report accuracy following exposure durations of 10, 20, 40, 80 and 160 ms. A partial-report technique was used, and each presentation of a letter row was immediately followed by the presentation of a masking stimulus. Each of 10 subjects received 840 trials which reflected 24 trials for each exposure-duration by position-probed combination. The letters at both ends of a row became available for report prior to the centre letters. In addition, report of the left-most letter was consistently better than report of the right-most letter, and report of the centre item at fixation improved at a more rapid rate with increased exposure duration than report of the other centre letters. This pattern of results provides support for certain components of several different previous proposals concerning the order in which individual items from multi-element displays become available for report.     

Word superiority over isolated letters: The neglected case of forward masking

Previous research shows that when briefly presented alphabetic stimuli are followed by pattern masks, letters in words are reported more accurately than are isolated letters (the “Word-Letter Phenomenon,” or WLP); however, when these masks are replaced by blank fields, the WLP disappears. These findings have led to the popular notion that the WLP reflects selective masking of ongoing stimulus processing and so critically depends on the use of poststimulus masks. Here we report three experiments which re-examine the role of masking in the WLP by contrasting the effects of postmasked displays with the effects of premasked displays in which words and isolated letters werepreceded by a pattern mask and followedby a completely blank field. Despite the critical role generally assigned to poststimulus pattern masks, similar WLPs were obtained with pre- and postmasked displays. Implications for theories of word and letter recognition are discussed.     

Saccadic eye movements during reading

Exposure duration and sequential redundancy are major determinants of report accuracy for textual displays. Increased emission of left-to-right saccades to both word strings and letter strings are associated with sequential redundancy. Such saccades are more frequent when words rather than pseudowords are viewed. The pattern of scanning is not simply left to right, and certain patterns of eye movements are associated positively with accuracy of report. These are a function of the sequential constraints of the display and are stronger for word strings than for letter strings. Presence of a word elicits more left-to-right saccades than does a pseudoword, even at exposures too short for a second fixation to be useful. In that case, there is no difference between redundant and nonredundant pseudowords. There is no redundancy effect at short exposures of pseudosentences.     

Identification and pronunciation effects in a verbal reaction time task for words,pseudowords, and letters

The question addressed in this investigation was whether faster reading and pronunciation of words than orthographically regular pseudowords is due to faster identification or to faster programming and execution of the motor response. In Experiment I, three different response conditions (naming, threechoice signaled responding, and one-choice signaled responding) were employed to separate the identification and articulation processes in a verbal reaction time task. It was found that, for all intents and purposes, single, isolated letters are processed as if they were very short words. Words are read and pronounced 72 msec faster than pseudowords. Words are also pronounced 30 msec faster than pseudowords even if the reader has longer than 1 sec to identify the stimulus (three-choice condition) or to both identify the stimulus and preprogram the response (one-choice condition). The data indicate that words are identified about 52 msec faster and articulated about 30 msec faster than pseudowords. Since the number of response alternatives (one or three) does not interact with stimulus type (letter, word, or pseudoword) in the signaled response control condition, the 30-msec difference is due to response execution and not to differential response programming. Response programming takes in the neighborhood of 236 msec. Experiment 2 investigated the effect of local orthographic context upon the identification of the first letter of a string of letters. No difference was found in identifying the initial letter of words and pseudowords, but the initial letter of these orthographically regular letter strings was identified and named 10 msec faster than the initial letter of orthographically anomalous strings of letters (anagrams). The data from the two experiments are supportive of theories of reading that assume (1) that the letters of visually presented words are processed simultaneously, in parallel, (2) that there is a relatively direct access and retrieval of the phonological memory codes for the names of words, and (3) that orthographically regular pseudowords having no representation in the phonological lexicon undergo a grapheme-to-phoneme transformation that takes longer to finish than the direct spelling-to-sound process used for words.     

Contrasting Effects of Letter-spacing in Alexia: Further Evidence that Different Strategies Generate Word Length Effects in Reading

The reading behaviour of two alexic patients (SA and WH) is reported. Both patients are severely impaired at reading single words, and both show abnormally strong effects of word length when reading. These two symptoms are characteristic of letter-by-letter reading. Experiment 1 examined the pattern of errors when the patients read large and small words. Further experiments examined the effects of inter-letter spacing on word naming (Experiments 2a and 2b) and the identification of letters in letter strings (Experiment 3). For both patients, letter identification was better for widely spaced letters in letter strings, and this effect was most pronounced for the central letters in the strings. This is consistent with abnormally strong flanker interference in letter identification. However, inter-letter spacing affected word reading behaviour in the two patients in different ways. SA's word reading improved with widely spaced letters; WH's word reading was disrupted. This suggests that these patients adopted different strategies when reading words. We conclude that several reading behaviours can elicit word length effects, and that these different behaviours can reflect strategic adaptation to a common functional deficit in patients. We discuss the implications both for understanding alexia and for models of normal word identification.