The N400 and the fourth grade shift

While behavioral and educational data characterize a fourth grade shift in reading development, neuroscience evidence is relatively lacking. We used the N400 component of the event‐related potential waveform to investigate the development of single word processing across the upper elementary years, in comparison to adult readers. We presented third graders, fourth graders, fifth graders, and college students with a well‐controlled list of real words, pseudowords, letter strings, false font strings, and animal name targets. Words and pseudowords elicited similar N400s across groups. False font strings elicited N400s similar to words and letter strings in the three groups of children, but not in college students. The pattern of findings suggests relatively adult‐like semantic and phonological processing by third grade, but a long developmental time course, beyond fifth grade, for orthographic processing in this context. Thus, the amplitude of the N400 elicited by various word‐like stimuli does not reflect some sort of shift or discontinuity in word processing around the fourth grade. However, the results do suggest different developmental time courses for the processes that contribute to automatic single word reading and the integrative N400.     

Developmental changes in neural letter‐selectivity: A 1‐year follow‐up of beginning readers

The developmental course of neural tuning to visual letter strings is unclear. Here we tested 39 children longitudinally, at the beginning of grade 1 (6.45 ± 0.33 years old) and 1 year after, with fast periodic visual stimulation in electroencephalography to assess the evolution of selective neural responses to letter strings and their relationship with emerging reading abilities. At both grades, frequency‐tagged letter strings were discriminated from pseudofont strings (i.e. letter‐selectivity) over the left occipito‐temporal cortex, with effects observed at the individual level in 62% of children. However, visual words were not discriminated from pseudowords (lexical access) at either grade. Following 1 year of schooling, letter‐selective responses showed a specific increase in amplitude, a more complex pattern of harmonics, and were located more anteriorly over the left occipito‐temporal cortex. Remarkably, at both grades, neural responses were highly significant at the individual level and correlated with individual reading scores. The amplitude increase in letter‐selective responses between grades was not found for discrimination responses of familiar keyboard symbols from pseudosymbols, and was not related to a general increase in visual stimulation responses. These findings demonstrate a rapid onset of left hemispheric letter selectivity, with 1 year of reading instruction resulting in increased emerging reading abilities and a clear quantitative and qualitative evolution within left hemispheric neural circuits for reading.     

A developmental, interactive activation model of the word superiority effect

Parallel distributed processing (PDP) models of reading developed out of an appreciation of the role that context plays in letter and word perception. Adult readers can more accurately identify letters in a word than alone or in other random display contexts, a phenomenon known as the Word Superiority Effect (WSE). We examined the effects of orthographic context on the letter recognition skills of dyslexic children, comparing their performance to adults, and chronological- and reading-age matched groups. Consistent with previous studies, results showed adults better able to identify letters in the context of words and pseudowords than in random letter strings. Young normal readers demonstrated the WSE, but their pseudoword advantage was less than adults. The dyslexic children showed no WSE at all. PDP computer simulations for the experimental data using the Interactive Activation model (IA) suggested that the orthographic components of the lexical system of normal children are interactive and distributed as they are in adults but provide less bottom-up activation. In addition, top-down processing increases with age and reading skill, but may be absent for dyslexic readers.     

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.     

Behavioral and brain wave evidence for automatic processing of orthographically regular letter strings

Evidence for the automatic processing of nonword letter strings was sought in subjects who performed two different perceptual tasks. Twelve subjects detected valid words. Twelve other subjects detected Gestalt patterns that contained no letters. The targets and two types of nonword letter strings were interspersed in a stream of nonletter images. Behavioral data showed significant effects of orthographic regularity of letter strings in the group that detected words, but not in the group that detected Gestalt patterns. Brain-wave responses showed the effect of orthographic regularity in both groups. The responses were significantly larger for regular than for irregular strings. This showed that brain waves can be used to study the operation of reading processes in subjects who are performing a task that does not require reading ability.     

Orthographic contributions to perceived word center

We have a surprising tendency to misperceive the center of visually presented words (). To understand the origin of this bias, four experiments assessed the impact of letter font, letter size, and grapheme-phoneme convergences on perceived stimulus center. Fourteen observers indicated the perceived centers of words, pseudowords, consonant strings, and lines with a mouse cursor. Visual orthographic factors had no effect on perceived word center but grapheme-phoneme convergence did: Observers compensated for strong grapheme-phoneme asymmetries in the letter strings. These findings support the idea that the cognitive representation of words is spatially distorted as a result of lexical access mechanisms.     

Zeading and reazing: which is faster? The position of the diverging letter in a pseudoword determines reading time

We present evidence that (a) at least some components of the reading process are serial and (b) pseudoword reading is affected by lexical knowledge, even in a transparent orthographic system like Italian. Pseudowords deriving from five-letter words by changing either the first or the fourth letter were presented for reading aloud. Results showed an effect of the position of the diverging letter: Early diverging pseudowords were read more slowly than late diverging pseudowords. The dual-route cascaded (DRC) model (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001) successfully simulated the behavioural data.     

Levels of representation in word processing

Abstract

Four experiments are described examining the effects of words frequency, orthographic structure, and letter spacing on a range of tasks designed to tap different levels of representation in word processing. In Experiment 1, the task was lexical decision. Effects of both frequency (high-frequency words were recognized faster than low-frequency words) and orthographic regularity (illegal non-words were rejected faster than legal non-words) were found. In Experiment 2 subjects had to detect a rotated letter within the letter strings. Effects of orthographic structure emerged, with a marked disadvantage for illegal non-words with respect to the other types of string. No difference was found among high-frequency words, lowfrequency words and legal non-words. In Experiment 3, subjects had to detect a letter elevated above the horizontal plan with respect to the rest of the string. Effects of both spatial arrangement of letters and number of letters were found (spaced strings were responded to less accurately than non-spaced strings and seven-letter extra-spaced strings were responded to slower than the other strings). Neither lexical nor orthograpic variables affected this task. In Experiment 4 subjects had to detect the presence of a bold segment contained in one of the letters in the strings. Performance was unaffected by both lexical and spatial variables. The pattern of results is discussed with reference to a multi-stage model of word recognition in which lexical and spatial variables affect processing at different stages. At a feature map level, in which features are extracted from the discontinuities of light intensities, processing is independent of both spatial and lexical factors. At a letter-shape map level, in which spatial relationships between features are coded, spacing between letters affects encoding. At a graphemic map level, in which letter identities and their relative positions within strings are coded, orthographic variables have an effect. Lexicality and frequency affect only subsequent stages of processing, when stored lexical information is retrieved (e.g. for lexical decision).     

The role of visual spatial attention in adult developmental dyslexia

The present study investigated the nature of visual spatial attention deficits in adults with developmental dyslexia, using a partial report task with five-letter, digit, and symbol strings. Participants responded by a manual key press to one of nine alternatives, which included other characters in the string, allowing an assessment of position errors as well as intrusion errors. The results showed that the dyslexic adults performed significantly worse than age-matched controls with letter and digit strings but not with symbol strings. Both groups produced W-shaped serial position functions with letter and digit strings. The dyslexics' deficits with letter string stimuli were limited to position errors, specifically at the string-interior positions 2 and 4. These errors correlated with letter transposition reading errors (e.g., reading slat as “salt”), but not with the Rapid Automatized Naming (RAN) task. Overall, these results suggest that the dyslexic adults have a visual spatial attention deficit; however, the deficit does not reflect a reduced span in visual–spatial attention, but a deficit in processing a string of letters in parallel, probably due to difficulty in the coding of letter position.     

Dissociation of mechanisms of reading in Alzheimer's disease.

The role of spelling-to-sound correspondence rules in oral word reading was investigated by asking patients with Alzheimer's Disease (AD) and normal controls to read aloud pronounceable letter strings that do not happen to be real words. These pseudowords were of two types: those that have orthographically similar "neighbors," and those that have no neighbors. The patients with AD were mildly impaired relative to the normal controls in reading pseudowords with neighbors, but were markedly impaired in reading pseudowords with no neighbors. The results are interpreted as favoring a model of reading in which words and pseudowords are normally read via the same lexical mechanism. An ancillary route involving the conscious application of spelling-to-sound rules is available only to cognitively intact readers.     

Isolating visual units in the perception of words and nonwords

In three experiments, reaction times for same-different judgments were obtained for pairs of words, pronounceable nonwords (pseudowords), and unpronounceable nonwords. The stimulus strings were printed either in a single letter case or in one of several mixtures of upper- and lowercase letters. In Experiment 1, the stimuli were common one- and two-syllable words; in Experiment 2, the stimuli included both words and pseudowords; and in Experiment 3, words, pseudowords, and nonwords were used. The functional visual units for each string type were inferred from the effects that the number and placement of letter case transitions had onsame reaction time judgments. The evidence indicated a preference to encode strings in terms of multiletter perceptual units if they are present in the string. The data .also suggested that whole words can be used as functional visual units, although the extent of their use depends on contextual parameters such as knowledge that a word will be presented.     

The primacyof visual information inthe analysis of letter strings

In Experiment 1, orthographic and phonetic information were separated by using artificial letters to represent English pseudowords and random letter strings. Subjects could learn to distinguish combinations of artificial letters on the basis of (1) orthographic, but not phonetic, information, (2) orthographic and phonetic information, (3) paired-associate verbal labels without orthographic information, and (4) neither orthographic nor phonetic information. By imposing a variety of response deadlines it appeared that subjects quickly exploited orthographic information without any contribution from phonetic correspondences. The only suggestion of a phonetic effect occurred in the absence of orthographic information and at longer latencies. Experiment 3 (using English letters) also suggested that phonetic information influenced the analysis of letter string pairs at only longer latencies, after visual analysis. Experiment 2 provided a demonstration that orthographic rules similar to those exploited in Experiment 1 were useful in visual discriminations regardless of the particular letter position affected by those rules. The results strain phonetic mediation models of performance in word-related tasks (e. g., Spoehr & Smith, 1975)and support models that emphasize visual analysis(Barron & Baron, 1977; Massaro, 1975; Pollatsek, Well, & Schindler, 1975).     

The acronym superiority effect

The visual world is replete with noisy, continuous, perceptually variant linguistic information, which fluent readers rapidly translate from percept to meaning. What are the properties the language comprehension system uses as cues to initiate lexical/semantic access in response to some, but not all, orthographic strings? In the behavioral, electromagnetic, and neuropsychological literatures, orthographic regularity and familiarity have been identified as critical factors. Here, we present a study in the Reicher—Wheeler tradition that manipulates these two properties independently through the use of four stimulus categories: familiar and orthographically regular words, unfamiliar but regular pseudowords, unfamiliar illegal strings, and familiar but orthographically illegal acronyms. We find that, like letters in words and pseudowords, letters in acronyms enjoy an identification benefit relative to similarly illegal, but unfamiliar strings. This supports theories of visual word recognition in which familiarity, rather than orthographic regularity, plays a critical role in gating processing.     

Rapid processing of letters,digits and symbols: what purely visual‐attentional deficit in developmental dyslexia?

Visual‐attentional theories of dyslexia predict deficits for dyslexic children not only for the perception of letter strings but also for non‐alphanumeric symbol strings. This prediction was tested in a two‐alternative forced‐choice paradigm with letters, digits, and symbols. Children with dyslexia showed significant deficits for letter and digit strings but not for symbol strings. This finding is difficult to explain for visual‐attentional theories of dyslexia which postulate identical deficits for letters, digits and symbols. Moreover, dyslexics showed normal W‐shaped serial position functions for letter and digit strings, which suggests that their deficit is not due to an abnormally small attentional window. Finally, the size of the deficit was identical for letters and digits, which suggests that poor letter perception is not just a consequence of the lack of reading. Together then, our results show that symbols that map onto phonological codes are impaired (i.e. letters and digits), whereas symbols that do not map onto phonological codes are not impaired. This dissociation suggests that impaired symbol‐sound mapping rather than impaired visual‐attentional processing is the key to understanding dyslexia.     

The neurobiology of adaptive learning in reading: A contrast of different training conditions

fMRI was used to investigate the separate influences of orthographic, phonological, and semantic processing on the ability to learn new words and the cortical circuitry recruited to subsequently read those words. In a behavioral session, subjects acquired familiarity for three sets of pseudowords, attending to orthographic, phonological, or (learned) semantic features. Transfer effects were measured in an event-related fMRI session as the subjects named trained pseudowords, untrained pseudowords, and real words. Behaviorally, phonological and semantic training resulted in better learning than did orthographic training. Neurobiologically, orthographic training did not modulate activation in the main reading regions. Phonological and semantic training yielded equivalent behavioral facilitation but distinct functional activation patterns, suggesting that the learning resulting from these two training conditions was driven by different underlying processes. The findings indicate that the putative ventral visual word form area is sensitive to the phonological structure of words, with phonologically analytic processing contributing to the specialization of this region.     

Better the DVL you know: acronyms reveal the contribution of familiarity to single-word reading

Current theories of reading are divided between dual-route accounts, which propose that separable processes subserve word recognition for orthographically regular and irregular strings, and connectionist models, which propose a single mechanism mapping form to meaning. These theories make distinct predictions about the processing of acronyms, which can be orthographically illegal and yet familiar, as compared with the processing of pseudowords, which are regular but unfamiliar. This study examined whether acronyms are processed like pseudowords and words. Event-related potentials (ERPs) were recorded as subjects viewed familiar and unfamiliar acronyms, words, pseudowords, illegal strings, and--as the targets of the substantive behavioral task--proper names. Familiar acronyms elicited repetition effects on the N400 component, a functionally specific index of semantic activation processes; repetition effects for familiar acronyms were similar in magnitude, timing, and scalp distribution to those for words and pseudowords. The similarity of the brain response to familiar--but--illegal and unfamiliar--but--legal classes of stimuli is inconsistent with predictions of dual-route models of reading.     

Preliminary letter identification in the perception of words and nonwords.

Words with mixed uppercase and lowercase letters (e.g. fAdE) were perceived more accurately than mixed-case pseudowords (e.g. gAdE), and mixed-case pseudowords were perceived more accurately than mixed-case unrelated letter strings (e.g. eFdT). In addition, same-case words were perceived more accurately than their mixed-case counterparts. The same held true for pseudowords but not for unrelated letter strings. The results are compatible with the view that both letter identify and visual form information are used in word perception.     

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.