The effects of forced serial processing on identification of words and random letter strings

Skilled readers identified words and random letter strings displayed one letter at a time on the screen of a computer-controlled oscilloscope. Letters were either displayed in a single position, or painted left-to-right in adjacent positions. Adjacent displays were either unmasked, masked by a letter-like pattern following each letter (backward masking) or masked by a pattern preceding each letter (forward masking). Unmasked words were identified with a high degree of accuracy, and accuracy was independent of the exposure duration of the letters over the range 50–200 msec. Masked adjacent word displays and one-position word displays were identified much less accurately, and accuracy was highly dependent on letter exposure duration. In contrast to these results, identification of random strings, or of letters within random strings, was almost unaffected by the presence of the mask and was dependent on letter exposure duration under all display conditions. The results are interpreted as evidence that (a) masking forces subjects to process serial displays one letter at a time, and (b) words, or large segments of words, are habitually processed in parallel, while random strings are processed as a series of individual letters or small chunks.     

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.     

Effects of concurrent spatial and verbal memory loads on serial position functions of laterally presented letter strings

In this study the influence of visuospatial and verbal memory loads on the identification of laterally presented letter strings was investigated. In the asymmetry task without concurrent loads, a clear right visual field advantage for letter identification was obtained. Hemisphere-specific effects due to concurrent loads were particularly observed when the difficulty of the load tasks was increased. The effects of visuospatial loads were found to be sex related, suggesting that under heavy load conditions mental rotation selectively overloads the processing capacity of the right hemisphere in males, while in females capacity limitations were observed in both hemispheres. Concurrent visuospatial loads produced more facilitation (or less interference) for letters in the outermost positions of each visual field than for letters in the innermost positions of each visual field. The results of the verbal memory load tasks revealed that an easy verbal load task facilitated performance which was particularly manifest for the right-most letter of both the left visual field and the right visual field. A difficult verbal memory load task interfered with recognition accuracy of letters which was most marked for the center letter in the right visual field. Letter position effects obtained in this study were interpreted in terms of various processing mechanisms influencing the serial position curves.     

On coding the position of letters in words: a test of two models

Open-bigram and spatial-coding schemes provide different accounts of how letter position is encoded by the brain during visual word recognition. Open-bigram coding involves an explicit representation of order based on letter pairs, while spatial coding involves a comparison function operating over representations of individual letters. We identify a set of priming conditions (subset primes and reversed interior primes) for which the two types of coding schemes give opposing predictions, hence providing the opportunity for strong scientific inference. Experimental results are consistent with the open-bigram account, and inconsistent with the spatial-coding scheme.     

Episodic effects on the visual comparison of letters in words

In two experiments, subjects compared the identity of either the first letters of displays or all the letters in displays. Words yielded faster decisions than did pseudowords (pronounceable items derived by changing a vowel in a word) only when entire displays were compared. In a training phase run before the comparison task, subjects had written down either the first letters or entire displays. Relative to items that had not appeared in the training phase, prior experience at writing entire displays facilitatedsame decisions about entire displays and interfered withdifferent decisions about entire displays. Prior experiences did not moderate the processing of first-letter identities. It was concluded that episodic effects arise from the interaction of higher order information underlying lexical encoding. Prelexical processing of letters is not sensitive to episodic effects.     

Letter processing in the visual system: different activation patterns for single letters and strings

One would expect that a lifetime of experience recognizing letters would have an important influence on the visual system. Surprisingly, there is limited evidence of a specific neural response to letters over visual control stimuli. We measured brain activation during a sequential matching task using isolated characters (Roman letters, digits, and Chinese characters) and strings of characters. We localized the visual word form area (VWFA) by contrasting the response to pseudowords against that for letter strings, but this region did not show any other sign of visual specialization for letters. In addition, a left fusiform area posterior to the VWFA was selective for letter strings, whereas a more anterior left fusiform region showed selectivity for single letters. The results of different analyses using both large regions of interest and inspections of individual patterns of response reveal a dissociation between selectivity for letter strings and selectivity for single letters. The results suggest that reading experience fine-tunes visual representations at different levels of processing. An important conclusion is that the processing of nonpronounceable letter strings cannot be assumed to be equivalent to single-letter perception.     

Episodic effects on the visual comparison of letters in words.

In two experiments, subjects compared the identity of either the first letters of displays or all the letters in displays. Words yielded faster decisions than did pseudowords (pronounceable items derived by changing a vowel in a word) only when entire displays were compared. In a training phase run before the comparison task, subjects had written down either the first letters or entire displays. Relative to items that had not appeared in the training phase, prior experience at writing entire displays facilitated same decisions about entire displays and interfered with different decisions about entire displays. Prior experiences did not moderate the processing of first-letter identities. It was concluded that episodic effects arise from the interaction of higher order information underlying lexical encoding. Prelexical processing of letters is not sensitive to episodic effects.     

Visual word recognition of three-letter words as derived from the recognition of the constituent letters

Word recognition is one of the basic processes involved in reading. In this connection, a model for word recognition is proposed consisting of a perceptual and a decision stage. It is supposed that, in the perceptual stage, the formation of possible words proceeds by separate identification of each of the letters of the stimulus word in their positions. Letter perception is taken to be conditional on position because of interaction effects from neighboring letters. These effects are dependent on both position in the word and retinal eccentricity, which are of particular relevance in reading. The letter-based approach rests on the strong relationship between the results from single-letter recognition in meaningless strings and in real words. Next, in the decision step, the many alternatives generated in the perceptual stage are matched with a vocabulary of real words. It is supposed that the final choice from among the remaining words is made in accordance with the constant ratio rule; frequency effects are not separately incorporated in the model. All predictions of the model are generated by means of data from earlier experiments. Despite being not optimally suited for this purpose, the predictions compare favorably with responses in word-recognition experiments.     

Multiple number and letter comparison: directionality and accessibility in numeric and alphabetic memories

In 3 experiments, subjects made comparativejudgments on a set of 2 numbers or letters, 3 numbers or letters, or 5 numbers or letters. Numeric and alphabetic serial order memories were contrasted. Three aspects of serial order memory processes were identified: computational complexity, directionality, and accessibility. Computational complexity is the number of algorithmic steps involved in identifying a target. Directional bias is measured as the speed differences in identifying serial targets of equal computational complexity in a stimulus array. Memory accessibility is measured as the numeric and alphabetic serial position effects. Subjects had a slight directional bias favoring backward ordering for single digits but no bias in 2-digit number ordering, in contrast to a strong forward directional advantage in letter ordering. The speed of number access was found to steadily and evenly decrease along the numeric scale, in contrast to a systematic pattern of variations in alphabet access along the alphabetic scale. Finally, the middle item effect (the middle item in a multi-item array is identified most slowly) found in Jou's (1997) multiple-letter comparison study was generalized to numbers.     

Nonsense strings,words, and sentences: Some cross-linguistic comparisons

Summary Three experiments were carried out in which strings of 15 syllables were presented to native German speakers. Each S heard the same string 25 times. In Exp. I, the strings were nonsense stems with no structure, morphological structure, or morphological and syntactic structure characteristic of the English language. In Exp. II, the strings were either a random list of English words or a meaningful sentence. In Exp. III, the strings were either a random list of German words or a meaningful sentence. In all the experiments, the strings were either monotone or intonated. The results of Exp. I confirmed the finding of O'Connell, Turner, and Onuska (1968) that linguistic structure facilitates recall. Facilitation was limited to intonated versions and localized at the high structure level (morphology and syntax). The remaining experiments indicated that, in strings of actual lexical items, the relative facilitative influence of intonation and structure depends on the redundance of the linguistic cues. In all experiments, the rate of speech production by Ss approached that of spontaneous speech as a function of both structure and intonation in the stimulus string.

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Zusammenfassung In 3 Experimenten wurden deutschsprachigen Vpn Ketten aus 15 Silben dargeboten. Jede Vp hörte dieselbe Kette 25mal. Die Ketten im ersten Experiment bestanden entweder aus sinnlosen Silben ohne jede Struktur, mit morphologischer Struktur oder mit morphologischer und syntaktischer Struktur. Alle Strukturmerkmale wurden der englischen Sprache entnommen. Die Ketten im zweiten Experiment stellten entweder eine Zufallsliste englischer Wörter oder einen sinnvollen Satz dar. Im dritten Experiment wurde eine Zufallsliste aus deutschen Wörtern oder ein sinnvoller Satz verwendet. In allen Experimenten wurden die Ketten entweder monoton oder intoniert dargeboten. Die Ergebnisse des ersten Experiments bestätigten den Befund von O'Connell, Turner, und Onuska (1968), daß die sprachliche Struktur zu einer Verbesserung der Wiedergabe führt. Diese Verbesserung trat nur bei der intonierten und hochstrukturierten Bedingung (Morphologie und Syntax) auf. Die übrigen Experimente zeigten, daß der Verbesserungseffekt von Intonation und Struktur in den Wortketten und Sätzen von den sprachlichen Cues abhängig ist. In allen Experimenten näherte sich die Sprechgeschwindigkeit der Vpn der Geschwindigkeit der spontanen Sprache als Funktion der Struktur und Intonation der Stimuluskette.

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The research reported in the following article has been supported by the Alexander von Humboldt Foundation of Bad Godesberg, Germany, and by the Psychological Institute of the Free University of Berlin. It was made possible by the generosity of Saint Louis University in granting the author a leave of absence for purposes of research. The assistance of Miss Sabine Kowal is gratefully acknowledged.     

Illusory words: the roles of attention and of top-down constraints in conjoining letters to form words

When attention is divided among four briefly exposed syllables, subjects mistakenly detect targets whose letters are present in the display but in the wrong combinations. These illusory conjunctions are somewhat more frequent when the target is a word and when the distractors are nonwords, but the effects of lexical status are small, and no longer reach significance in free report of the same displays. Search performance is further impaired if the nonwords are unpronounceable consonant strings rather than consonant-vowel-consonant strings, but the decrement is due to missed targets rather than to increased conjunction errors. The results are discussed in relation to feature-integration theory and to current models of word perception.