Integrating information across eye fixations in reading: the role of letter and word units

Eye movements and eye fixations were recorded to study the integration of letter/word information across interword fixations in reading. Two hypotheses were examined. One hypothesis posits that readers obtain effective information from the beginning two or three letters of a parafoveal word. This information facilitates the recognition of the word when it is being fixated. The alternative posits that effective information is obtained from the complete parafoveal word. The results of the present study showed faster reading rates when parafoveal previews comprised complete words than when they comprised beginning letters alone. Furthermore, the usability of parafoveally available partial word information from beginning and ending letters was not affected by small variations in retinal eccentricity. Both findings were taken as evidence that readers gain useful information from all letters of the parafoveally available word and that whole word information, rather than specific letter information, is integrated across interword fixations in reading.     

Word recognition cues for beginning and skilled readers

Three experiments are reported in which subjects chose from an array the response alternative that most resembled a nonsense stimulus trigram or quingram. Subjects could respond on the basis of individual letter positions or overall word shape. However, word shape was not manipulated independently of the individual letters that comprise the word as has been the case in previous studies. Kindergarten children and first graders who were poor readers showed a more varied pattern of responses than first graders who were good readers. With simple stimuli (trigrams), beginning and skilled readers chose alternatives on the basis of overall shape and the initial letter. With more complex stimuli (quingrams), the skilled readers continued choosing on the basis of word shape and initial letters, but beginning readers only chose on the basis of the first letter.     

Parafoveal letter-position coding in reading

The masked-priming lexical decision task has been the paradigm of choice for investigating how readers code for letter identity and position. Insight into the temporal integration of information between prime and target words has pointed out, among other things, that readers do not code for the absolute position of letters. This conception has spurred various accounts of the word recognition process, but the results at present do not favor one account in particular. Thus, employing a new strategy, the present study moves out of the arena of temporal- and into the arena of spatial information integration. We present two lexical decision experiments that tested how the processing of six-letter target words is influenced by simultaneously presented flanking stimuli (each stimulus was presented for 150 ms). We manipulated the orthographic relatedness between the targets and flankers, in terms of both letter identity (same/different letters based on the target’s outer/inner letters) and letter position (intact/reversed order of letters and of flankers, contiguous/noncontiguous flankers). Target processing was strongly facilitated by same-letter flankers, and this facilitatory effect was modulated by both letter/flanker order and contiguity. However, when the flankers consisted of the target’s inner-positioned letters alone, letter order no longer mattered. These findings suggest that readers may code for the relative position of letters using words’ edges as spatial points of reference. We conclude that the flanker paradigm provides a fruitful means to investigate letter-position coding in the fovea and parafovea.     

Transposed-letter effects in reading: evidence from eye movements and parafoveal preview

Three eye movement experiments were conducted to examine the role of letter identity and letter position during reading. Before fixating on a target word within each sentence, readers were provided with a parafoveal preview that differed in the amount of useful letter identity and letter position information it provided. In Experiments 1 and 2, previews fell into 1 of 5 conditions: (a) identical to the target word, (b) a transposition of 2 internal letters, (c) a substitution of 2 internal letters, (d) a transposition of the 2 final letters, or (e) a substitution of the 2 final letters. In Experiment 3, the authors used a further set of conditions to explore the importance of external letter positions. The findings extend previous work and demonstrate that transposed-letter effects exist in silent reading. These experiments also indicate that letter identity information can be extracted from the parafovea outside of absolute letter position from the first 5 letters of the word to the right of fixation. Finally, the results support the notion that exterior letters play important roles in visual word recognition.     

Taking a bright view of negative priming in the light of dim stimuli: further evidence for memory confusion during episodic retrieval.

A same-different letter-matching task was used to examine the effects of stimulus intensity on negative priming, which is poorer performance when target letters have been presented as distractor letters on the immediately preceding trial. In Experiment 1, stimulus intensity was manipulated between-participants, whereas in Experiment 2, it varied randomly from trial-to-trial within-participants. In Experiment 1, negative priming was equivalent for both stimulus intensities. In Experiment 2, negative priming effects were larger for repeated intensity stimuli than for nonrepeated intensity stimuli, when stimulus intensity was dim. Furthermore, for repeated intensity stimuli, negative priming effects were enhanced when the overt response required to the stimulus was repeated from prime to probe trial. These results are consistent with the hypothesis that negative priming may be due to memory confusion, rather than to inhibition of the distractor stimuli.     

The relative position priming effect depends on whether letters are vowels or consonants

The relative position priming effect is a type of subset priming in which target word recognition is facilitated as a consequence of priming the word with some of its letters, maintaining their relative position (e.g., csn as a prime for casino). Five experiments were conducted to test whether vowel-only and consonant-only subset primes contribute equally to this effect. Experiment 1 revealed that this subset priming effect emerged when primes were composed exclusively of consonants, compared with vowel-only primes (csn-casino vs. aia-animal). Experiment 2 tested the impact of letter frequency in this asymmetry. Subset priming effects were obtained for both high- and low-frequency consonants but not for vowels, which rules out a letter frequency explanation. Experiment 3 tested the role of phonology and its contribution to the priming effects observed, by decreasing the prime duration. The results showed virtually the same effects as in the previous experiments. Finally, Experiments 4 and 5 explored the influence of repeated letters in the primes on the magnitude of the priming effects obtained for consonant and vowel subset primes (iuo-dibujo and aea-madera vs. mgn-imagen and rtr-frutero). Again, the results confirmed the priming asymmetry. We propose that a functional distinction between consonants and vowels, mainly based on the lexical constraints imposed by each of these types of letters, might provide an explanation for the whole set of results.     

Integrating information across eye movements

A series of experiments was conducted in which a word initially appeared in parafoveal vision, followed by the subject's eye movement to the stimulus. During the eye movement, the initially displayed word was replaced by a word which the subject read. Under certain conditions, the prior parafoveal word facilitated naming the foveal word. Three alternative hypotheses were explored concerning the nature of the facilitation. The verbalization hypothesis suggests that information acquired from the parafoveal word permits the subject to begin to form the speech musculature properly for saying the word. The visual features integration hypothesis suggests that visual information obtained from the parafoveal word is integrated with foveal information after the saccade. The preliminary letter identification hypothesis suggests that some abstract code about the letters of the parafoveal word is stored and integrated with information available in the fovea after the saccade. The results of the experiments supported the latter hypothesis in that information about the beginning letters of words was facilitatory in the task. The other two hypotheses were disconfirmed by the results of the experiments.     

Global,component, and serial processing of printed words in beginning reading

Nonreaders (end of kindergarten) and beginning readers (end of first grade) were compared. Both nonreaders and beginning readers imposed integral perceptual structures on shape/terminal letter information and configural perceptual structures on medial letter information: visual attention varied as a function of the unit of visual information but not as a function of learning to read. Nonreaders remembered a word more accurately than a letter in a word, showing visual origins of the word superiority effect. Beginning readers remembered a word faster than a letter in a word, which they remembered faster than a letter sequence in a word, suggesting early origins of the word priority effect. Only gains in memory for a letter sequence correlated with gains in word decoding. Throughout first grade, sentence verification was faster, not more accurate, when sentences were presented normally compared to one word at a time; repeated exposure of a word in parafoveal and foveal vision facilitates speed but not accuracy of comprehension. Results are discussed in reference to a model of global, component, and serial procedures.     

Independent priming of location and color in identification of briefly presented letters

Attention shifts are facilitated if the items to be attended remain the same across trials. Some researchers argue that this priming effect is perceptual, whereas others propose that priming is postperceptual, involving facilitated response selection. The experimental findings have not been consistent regarding the roles of variables such as task difficulty, response repetition, expectancies, and decision-making. Position priming, when repetition of a target position facilitates responses on a subsequent trial, is another source of disagreement among researchers. Experimental results have likewise been inconsistent as to whether position priming is dependent on the repetition of target features or has an independent effect on attention shifts. We attempted to isolate the perceptual components of priming by presenting brief (10–180 ms) search arrays to eight healthy observers. The task was to identify a color-singleton letter among distractors. All stimulus presentation contingencies were randomized, and responses were unspeeded, to avoid effects of observer expectation and postperceptual effects. Repeating target color and/or position strongly improved performance. The effects of color and position repetition were independent of one another and were stable across participants. The results argue for a strong perceptual component in priming, which biases selection toward recent target features and positions, showing that perceptual mechanisms are sufficient to produce priming in visual search and that such effects can be elicited with limited sensory evidence. The results are the first to demonstrate independent priming of color and position in the identification of briefly presented, postmasked stimuli.     

Graded effects of number of inserted letters in superset priming

Three masked priming experiments investigated the effects of target word length and number of inserted letters on superset priming, where irrelevant letters are added to targets to form prime stimuli (e.g., tanble-table). Effects of one, two, three, and four-letter insertions were measured relative to an unrelated prime condition, the identity prime condition, and a condition where the order of letters of the superset primes was reversed. Superset primes facilitated performance compared with unrelated primes and reversed primes, and the overall pattern showed a small cost of letter insertion that was independent of target word length and that increased linearly as a function of the number of inserted letters. A meta-analysis incorporating data from the present study and two other studies investigating superset priming, showed an average estimated processing cost of 11 ms per letter insertion. Models of letter position coding are examined in the light of this result.     

Eye movements when reading: The importance of the word to the left of fixation

In reading, it is well established that word processing can begin in the parafovea while the eyes are fixating the previous word. However, much less is known about the processing of information to the left of fixation. In two experiments, this issue was explored by combining a gaze-contingent display procedure preventing parafoveal preview and a letter detection task. All words were displayed as a series of xs until the reader fixated them, thereby preventing forward parafoveal processing, yet enabling backward parafoveal or postview processing. Results from both experiments revealed that readers were able to detect a target letter embedded in a word that was skipped. In those cases, the letter could only have been identified in postview (to the left of fixation), and detection rate decreased as the distance between the target letter and the eyes' landing position increased. Most importantly, for those skipped words, the typical missing-letter effect was observed with more omissions for target letters embedded in function than in content words. This can be taken as evidence that readers can extract basic prelexical information, such as the presence of a letter, in the parafoveal area to the left of fixation. Implications of these results are discussed in relation to models of eye movement control in reading and also in relation to models of the missing-letter effect.     

Specialization of the cerebral hemispheres in scanning for information in short-term memory

Lateral specialization of function in the cerebral hemispheres was investigated in the context of a memory scanning paradigm. The S first memorized a set of letters (the memory set) and then indicated whether or not a subsequent test stimulus, presented in either the right or left visual field, matched any letter in the set. The test stimulus was either a letter or a picture of some common object; for the picture, S’s response was based on the initial letter of the name of that object. Reaction time was recorded and plotted as a function of the number of letters in the memory set. The results support the hypothesis that in a memory scanning task of this type, letter and picture test stimuli are spatially and verbally represented, respectively, and are processed in different cerebral hemispheres.     

Lexical integration across saccades in reading

Summary Eye movements were recorded during sentence reading to examine the integration of parafoveal text across fixations. Four viewing conditions were used, each affording full view of the directly fixated word: no preview of the spatially adjacent parafoveal word; preview of its beginning trigram; preview of its beginning four letters; or preview of all its constituent letters. The magnitude of parafoveal-preview benefits (the difference between the no-preview condition and the different parafoveal-preview conditions) was examined as a function of the size of the saccade to the parafoveal target and as a function of the subsequent fixation location at the previewed target. The results revealed no effects of saccade size on parafoveal-preview benefits, but large effects of fixation position during the initial target fixation. Furthermore, parafoveal previews were used during the initial target fixation and during subsequent intratarget refixations. The results support a lexical-text-integration hypothesis which posits that lexical information is integrated across interword fixations and intraword refixations.     

On the nature of consonant/vowel differences in letter position coding: Evidence from developing and adult readers

In skilled adult readers, transposed‐letter effects (jugde ‐JUDGE ) are greater for consonant than for vowel transpositions. These differences are often attributed to phonological rather than orthographic processing. To examine this issue, we employed a scenario in which phonological involvement varies as a function of reading experience: A masked priming lexical decision task with 50‐ms primes in adult and developing readers. Indeed, masked phonological priming at this prime duration has been consistently reported in adults, but not in developing readers (Davis, Castles, & Iakovidis, 1998). Thus, if consonant/vowel asymmetries in letter position coding with adults are due to phonological influences, transposed‐letter priming should occur for both consonant and vowel transpositions in developing readers. Results with adults (Experiment 1) replicated the usual consonant/vowel asymmetry in transposed‐letter priming. In contrast, no signs of an asymmetry were found with developing readers (Experiments 2–3). However, Experiments 1–3 did not directly test the existence of phonological involvement. To study this question, Experiment 4 manipulated the phonological prime‐target relationship in developing readers. As expected, we found no signs of masked phonological priming. Thus, the present data favour an interpretation of the consonant/vowel dissociation in letter position coding as due to phonological rather than orthographic processing.     

Masked constituent letter priming in an alphabetic decision task

Abstract

The experiments presented here were designed to test whether the prior presentation of a letter in a word, nonword or a string of Xs facilitates the subsequent identification of this letter. Using briefly presented masked primes, clear facilitatory constituent priming effects were obtained in an alphabetic decision task (letter/non-letter classification) when prime letters were flanked by Xs, but the effects disappeared or were greatly reduced when the prime letter formed part of a consonant array (nonword primes). Evidence for word-letter constituent priming was also obtained but almost only for word-initial letten. These facilitatory constituent priming effects were strongest when the target letter was embedded in a string of hash marks and occupied the same relative position in this string as the prime letter in the prime string. The mediating role of letter representations in word recognition and the position-specific coding of character arrays are discussed in the light of these results.     

Priming and intrusion errors in RSVP streams with two response dimensions

Loach and Marí-Beffa (Vis Cogn, 10:513-526, 2003) observed that a distractor stimulus, presented immediately after a behaviorally relevant target stimulus, negatively primed a related probe stimulus indicating that the distractor had been inhibited. They argued that "post-target inhibition" may be a mechanism for preventing interference from temporally proximal stimuli; interference that could potentially result in a binding/intrusion error. In order to test this hypothesis, the authors carried out two rapid serial visual presentation (RSVP) experiments in which participants had to report either the identity (Experiment 1) or color (Experiment 2) of a target letter surrounded by distractor letters. In Experiment 1, a close relationship between priming and errors was observed. When a distractor stimulus showed evidence of being inhibited the participant was less likely to commit a binding error. The opposite was true when a distractor stimulus showed evidence of being facilitated. The results of Experiment 2 showed limited evidence of the same relationship.     

Letter identification and lateral masking in dyslexic and average readers

Lateral masking and letter identification in dyslexic and average readers were investigated with a methodology that corrected for some of the weaknesses of the Geiger and Lettvin studies (1986, 1987). Target letters were presented alone or embedded within three-letter arrays at retinal locations from 0 degrees to 15 degrees to the right or left of a fixation point. A foveal letter, which was the same as or different from a target letter, appeared as a distractor, and comparisons were made between scaled and unscaled stimuli. Dyslexic readers were found to be better than average readers at detecting scaled letters embedded in an array in some of the peripheral locations tested. Unlike the results of Geiger and Lettvin, however, this finding of better letter detection in the periphery by dyslexics was limited to selected conditions of the study. Reading groups were also found to differ in responding to the foveal distractor in the letter task. Detection of letters by average readers was affected by the type of distractor, but this variable was not found to influence the dyslexic readers. These findings suggest some differences between dyslexic and average readers in attention to stimuli presented at multiple locations in the visual field.     

Letter-position coding in random consonant arrays

The processing of letter-position information in randomly arranged consonant strings was investigated using a masked prime variant of the alphabetic decision (letter/nonletter classification) task. In Experiment 1, primes were uppercase consonant trigrams (e.g., FMH) and targets were two uppercase Xs accompanied by the target letter or a nonletter (e.g., XMX, X%X). Response times were systematically faster when target letters were present in the prime string than when target letters were not present in the prime string. These constituent letter-priming effects were significantly stronger when the target letter appeared in the same position in the prime and target stimuli. This contrast between position-specific and position-independent priming was accentuated when subjects responded only when all the characters in the target string were letters (multiple alphabetic decision) in Experiments 2 and 3. In Experiment 4, when prime exposure duration was varied, it was found that position-specific priming develops earlier than position-independent priming. Finally, Experiment 5 ruled out a perceptual-matching interpretation of these results. An interpretation is offered in terms of position-specific and position-independent letter-detector units in an interactiveactivation framework.     

Effects of prime-target spatial separation and attentional deployment on masked repetition priming

In two masked repetition priming experiments with letter stimuli, the positions of prime and target stimuli were varied horizontally from fixation. Priming effects did not interact with position when prime and target location covaried (Experiment 1A) but diminished with increasing prime eccentricity when targets were always centrally located (Experiment 1B). Two accounts of this pattern of priming effects were proposed that postulate two different mechanisms over and above effects of visual acuity. The integration account postulates degree of separation of prime and target stimuli as the critical factor, and the attentional account postulates spatial attention as the critical factor. The results of Experiment 2, in which prime and target positions were manipulated orthogonally, were in favor of the attentional account. Repetition priming did not vary as a function of whether or not primes and targets appeared at the same location, but target processing was facilitated independently of priming when targets appeared at the same location as primes, especially in the right visual field.     

Reading Ability and the Use of Context in Orthographic Information Processing

Reading ability and context use in orthographic processing during silent reading were investigated. Poor readers and reading-level matched controls were presented target words containing a letter substitution in two contrasting context conditions. The hypothesis was that presenting a word in a highly predictable context would induce readers to proceed through the text without completely processing orthographic units at lower processing levels in the hierarchy (e.g., constituent letters). This general context effect was found. Normal and poor readers did not differ in context dependency. Poor readers more often missed substitutions, regardless of context. Poor readers also processed orthographic information less accurately. Target letters located in final word position were missed most often. Substitutions located in high bigram-frequency letter clusters were more often missed, and this effect was independent of intraword location. The implications of these results for understanding poor readers' basic reading problems are discussed.