Orthographic neighborhood effects in the right but not in the left cerebral hemisphere

Lateralized displays reveal the perceptual locus of the syllable transposition effect in Korean

Studies of letter transposition effects in alphabetic scripts provide compelling evidence that letter position is encoded flexibly during reading, potentially during an early, perceptual stage of visual word recognition. Recent studies additionally suggest similar flexibility in the spatial encoding of syllabic information in the Korean Hangul script. With the present research, we conducted two experiments to investigate the locus of this syllabic transposition effect. In Experiment 1, lexical decisions for foveal stimulus presentations were less accurate and slower for four-syllable nonwords created by transposing two syllables in a base word as compared to control nonwords, replicating prior evidence for a transposed syllable effect in Korean word recognition. In Experiment 2, the same stimuli were presented to the right and left visual hemifields (i.e., RVF and LVF), which project both unilaterally and contralaterally to each participant's left and right cerebral hemisphere (i.e., LH and RH) respectively, using lateralized stimulus displays. Lexical decisions revealed a syllable transposition effect in the accuracy and latency of lexical decisions for both RVF and LVF presentations. However, response times for correct responses were longer in the LVF, and therefore the RH, as compared to the RVF/LH. As the LVF/RH appears to be selectively sensitive to the visual-perceptual attributes of words, the findings suggest that this syllable transposition effect partly finds its locus within a perceptual stage of processing. We discuss these findings in relation to current models of the spatial encoding of orthographic information during visual word recognition and accounts of visual word recognition in Korean.

The role of orthographic neighbourhood effects in lateralized lexical decision: a replication study and meta-analysis

The effect of orthographic neighbourhood size (N) on lexical decision reaction time differs when words are presented in the left or right visual fields. Evidence suggests a facilitatory N effect (i.e., faster reaction times for words with larger neighbourhoods) in the left visual field. However, the N effect in the right visual field remains controversial: it may have a weaker facilitative role or it may even be inhibitory. In a pre-registered online experiment, we replicated the interaction between N and visual field and provided support for an inhibitory N effect in the right visual field. We subsequently conducted a pre-registered systematic review and meta-analysis to synthesise the available evidence and determine the direction of N effects across visual fields. Based on the evidence, it would seem the effect is inhibitory in the right visual field. Furthermore, the size of the N effect is considerably smaller in the right visual field. Both studies revealed considerable heterogeneity between participants and studies, and we consider the implications of this for future work.

Intact word processing in developmental prosopagnosia

A wealth of evidence from behavioural, neuropsychological and neuroimaging research supports the view that face recognition is reliant upon a domain-specific network that does not process words. In contrast, the recent many-to-many model of visual recognition posits that brain areas involved in word and face recognition are functionally integrated. Developmental prosopagnosia (DP) is characterised by severe deficits in the recognition of faces, which the many-to-many model predicts should negatively affect word recognition. Alternatively, domain-specific accounts suggest that impairments in face and word processing need not go hand in hand. To test these possibilities, we ran a battery of 7 tasks examining word processing in a group of DP cases and controls. One of our prosopagnosia cases exhibited a severe reading impairment with delayed response times during reading aloud tasks, but not lexical decision tasks. Overall, however, we found no evidence of global word processing deficits in DP, consistent with a dissociation account for face and word processing.

Age of acquisition and imageability norms for base and morphologically complex words in English and in Spanish

The extent to which processing words involves breaking them down into smaller units or morphemes or is the result of an interactive activation of other units, such as meanings, letters, and sounds (e.g., dis-agree-ment vs. disagreement), is currently under debate. Disentangling morphology from phonology and semantics is often a methodological challenge, because orthogonal manipulations are difficult to achieve (e.g., semantically unrelated words are often phonologically related: casual-casualty and, vice versa, sign-signal). The present norms provide a morphological classification of 3,263 suffixed derived words from two widely spoken languages: English (2,204 words) and Spanish (1,059 words). Morphologically complex words were sorted into four categories according to the nature of their relationship with the base word: phonologically transparent (friend-friendly), phonologically opaque (child-children), semantically transparent (habit-habitual), and semantically opaque (event-eventual). In addition, ratings were gathered for age of acquisition, imageability, and semantic distance (i.e., the extent to which the meaning of the complex derived form could be drawn from the meaning of its base constituents). The norms were completed by adding values for word frequency; word length in number of phonemes, letters, and syllables; lexical similarity, as measured by the number of neighbors; and morphological family size. A series of comparative analyses from the collated ratings for the base and derived words were also carried out. The results are discussed in relation to recent findings.

Hemispheric differences in orthographic and semantic processing as revealed by event-related potentials

Differences in how the right and left hemispheres (RH, LH) apprehend visual words were examined using event-related potentials (ERPs) in a repetition paradigm with visual half-field (VF) presentation. In both hemispheres (RH/LVF, LH/RVF), initial presentation of items elicited similar and typical effects of orthographic neighborhood size, with larger N400s for orthographically regular items (words and pseudowords) than for irregular items (acronyms and meaningless illegal strings). However, hemispheric differences emerged on repetition effects. When items were repeated in the LH/RVF, orthographically regular items, relative to irregular items, elicited larger repetition effects on both the N250, a component reflecting processing at the level of visual form (orthography), and on the N400, which has been linked to semantic access. In contrast, in the RH/LVF, repetition effects were biased toward irregular items on the N250 and were similar in size across item types for the N400. The results suggest that processing in the LH is more strongly affected by wordform regularity than in the RH, either due to enhanced processing of familiar orthographic patterns or due to the fact that regular forms can be more readily mapped onto phonology.

Visual word learning in skilled readers of English

Three experiments are reported analysing the processes by which adult readers of English learn new written words. Visual word learning was simulated by presenting short (four-letter) and longer (seven-letter) nonwords repeatedly and observing the reduction in naming latencies and the convergence in reaction times (RTs) to shorter and longer items that are the hallmarks of visual word learning. Experiment 1 presented nonwords in ten consecutive blocks. Naming latencies reduced over the first four or five presentations. The effect of length on naming RTs was large in block 1 but non-significant after four or five presentations. Experiment 2 demonstrated some reduction in RTs to untrained nonwords following practice on a trained set, but the reduction was less than for the trained items and RTs to shorter and longer nonwords did not converge. Experiment 3 included a retest after seven days which showed some slowing of RTs compared with the end of the first session but also considerable retention of learning. We conclude that four to six exposures to novel words (nonwords) are sufficient to establish durable lexical representations that permit parallel processing of newly-learned words. The results are discussed in terms of theoretical models of reading and word learning.

Rehabilitation of spelling in a participant with a graphemic buffer impairment: the role of orthographic neighbourhood in remediating the serial position effect

Graphemic Output Buffer (GOB) disorder is defined as difficulty with the serial output of a sequence of letters in the output stage of the spelling process. In their rehabilitation study with a GOB patient, Sage and Ellis ( 2006 ) found that improvement on treated words generalised to untreated words from the same orthographic neighbourhoods as treated items, but not to other unrelated words. GOB patients frequently show a bow-shaped accuracy curve across letter positions, where letters at the middle positions are most error-prone. It may be that consistent letters at these middle letter positions across neighbourhoods modulate this effect. Spelling was treated using an Anagram and Copy Treatment (ACT) and generalisation to three untreated sets was examined: (1) neighbours of treated words with shared middle letters (e.g., clock-block), (2) neighbours with different medial position letters (e.g., clock-click), and (3) unrelated words (e.g., clock-puppy). Improvement was found for untreated neighbours with shared middle letters. There was no effect of training on the unrelated word set, and a negative impact on untreated neighbours with changed middle letters after the treatment. We attribute these results to top-down support from learned lexical representations, which facilitate spelling of untreated neighbours with shared middle letters but impede neighbours with changed middle letters. This latter result is attributed to interference from neighbours in the trained set strengthening competing letter representations at middle positions.

Location, location, location: how it affects the neighborhood (effect)

Reaction times in lexical decision are more sensitive to a words' length and orthographic-neighborhood density when the stimulus is presented to the left visual field (LVF) than to the right visual field (RVF). We claim that the length effect is equivalent to the neighborhood effect, and propose a novel explanation of why the LVF, but not the RVF, is sensitive to density, based on different firing rates of abstract-letter representations encoding letters falling in the LVF versus RVF. We support this proposal with a large-scale implemented model of lexical decision utilizing spiking units, which provides a reasonable fit to the data from the English Lexicon Project under simulated central presentation, while replicating the observed hemifield asymmetries under simulated lateralized presentation.

ERP evidence of hemispheric independence in visual word recognition

This study examined the capability of the left hemisphere (LH) and the right hemisphere (RH) to perform a visual recognition task independently as formulated by the Direct Access Model (Fernandino, Iacoboni, & Zaidel, 2007). Healthy native Hebrew speakers were asked to categorize nouns and non-words (created from nouns by transposing two middle letters) into man-made and natural categories while their performance and ERPs were recorded. The stimuli were presented parafoveally to the right and left visual fields. As predicted by the Direct Access Model, ERP data showed that both the left hemisphere and right hemisphere were able to differentiate between words and non-words as early as 170 ms post-stimulus; these results were significant only for the contralaterally presented stimuli. The N1 component, which is considered to reflect orthographic processing, was larger in both hemispheres in response to the contralateral than the ipsilateral presented stimuli. This finding provides evidence for the RH capability to access higher level lexical information at the early stages of visual word recognition, thus lending weight to arguments for the relatively independent nature of this process.

Disruption of spelling-to-sound correspondence mapping during single-word reading in patients with temporal lobe epilepsy

Processing and/or hemispheric differences in the neural bases of word recognition were examined in patients with long-standing, medically-intractable epilepsy localized to the left (N=18) or right (N=7) temporal lobe. Participants were asked to read words that varied in the frequency of their spelling-to-sound correspondences. For the right temporal lobe group, reaction times (RTs) showed the same pattern across spelling-to-sound correspondence conditions as previously reported for normal participants. For the left temporal lobe group, however, the pattern of RTs suggested a greater relative influence of orthographic frequency than rime frequency, such that performance was worse on words whose orthographic body was less frequent in the language. We discuss these results in terms of differences in processing between the two cerebral hemispheres: the results for the right-temporal lobe patients are taken to support connectionist models of reading as described for the dominant (left) hemisphere, while results for the left-temporal lobe patients support a view of the right hemisphere as relatively less sensitive to phonology and relatively more sensitive to orthography.

Symmetrical hemispheric priming in spatial neglect: a hyperactive left-hemisphere phenomenon?

Hemispheric rivalry models of spatial neglect suggest that the left hemisphere becomes hyperactive following right-hemisphere lesions since the two hemispheres normally exert an inhibitory influence on each other via callosal connections. Using a masked hemifield priming paradigm, we investigated whether the putative change in hemispheric balance involves other, higher-order abstract representational systems in spatial neglect. Participants consisted of 12 neglect patients with right-hemisphere damage and three groups of control participants, i.e., 12 young healthy controls, 10 age-matched healthy controls and 10 right-hemisphere patients without spatial neglect. In each trial, participants made semantic categorization about a centrally presented target word which was preceded by a masked prime flashed either to the left or right visual field. All three control groups exhibited strong left-hemisphere advantage in inhibitory syllabic priming, consistent with the known left-hemisphere dominance in lexical inhibition during reading. By contrast, neglect patients exhibited a symmetrical pattern of priming between the left and right visual fields. These results suggest that (1) the neglected hemifield can rapidly extract abstract information even from weak and normally non-perceptible visual stimuli, but that (2) the normal left hemispheric dominance in reading is absent in neglect patients probably because of the generalized hyperactivity of the left hemisphere. Our results demonstrate a covert behavioral change in spatial neglect which may reflect the altered inter-hemispheric balance in the bilateral word recognition system encompassing lexico-semantic memory.

Lexical competition is enhanced in the left hemisphere: evidence from different types of orthographic neighbors

Two divided visual field lexical decision experiments were conducted to examine the role of the cerebral hemispheres in orthographic neighborhood effects. In Experiment 1, we employed two types of words: words with many substitution neighbors (high-N) and words with few substitution neighbors (low-N). Results showed a facilitative effect of N in the left visual field (i.e., right hemisphere) and an inhibitory effect of N in the right visual field (left hemisphere). In Experiment 2, we examined whether the inhibitory effect of the higher frequency neighbors increases in the left hemisphere as compared to the right hemisphere. To go beyond the usual N-metrics, we selected words with (or without) higher frequency neighbors (addition, deletion, or transposition neighbors). Results showed that the inhibitory effect of neighborhood frequency is enhanced in the right visual field. We examine the implications of these findings for the orthographic coding schemes employed by the models of visual word recognition.

In your right mind: right hemisphere contributions to language processing and production

The verbal/nonverbal account of left and right hemisphere functionality is the prevailing dichotomy describing the cerebral lateralization of function. Yet the fact that the left hemisphere is the superior language processor does not necessarily imply that the right hemisphere is completely lacking linguistic ability. This paper reviews the growing body of research demonstrating that, far from being nonverbal, the right hemisphere has significant language processing strength. From prosodic and paralinguistic aspects of speech production, reception, and interpretation, to prelexical, lexical and postlexical components of visual word recognition; strong involvement of the right hemisphere is implicated. The evidence reviewed challenges the notion that language is solely a function of the "verbal" left hemisphere, indicating that the right cerebral hemisphere makes significant and meaningful contributions to normal language processing as well.

Transposed-letter and laterality effects in lexical decision

Two divided visual field lexical decision experiments were conducted to examine the role of the cerebral hemispheres in transposed-letter similarity effects. In Experiment 1, we created two types of nonwords: nonadjacent transposed-letter nonwords (TRADEGIA; the base word was TRAGEDIA, the Spanish for TRAGEDY) and two-letter different nonwords (orthographic controls: TRATEPIA). In Experiment 2, the controls were one-letter different nonwords (TRAGEPIA) instead of two-letter different nonwords (TRATEPIA). The effect of transposed-letter similarity was substantially greater in the right visual field (left hemisphere) than in the left visual field. Furthermore, nonwords created by transposing two letters were more competitive than the nonwords created by substituting one or two letters of a target word. We examine the implications of these findings for the models of visual word recognition.

When phonology fails: orthographic neighbourhood effects in dyslexia

Both cerebral hemispheres contain phonological, orthographic and semantic representations of words, however there are between-hemisphere differences in the relative engagement and specialization of the different representations. Taking orthographic processing for example, previous studies suggest that orthographic neighbourhood size (N) has facilitatory effects in the right but not the left hemispheres. To pursue the nature of this asymmetric N effect, in particular whether there are individual differences in such specialisation, we examined N in a case of developmental dyslexia, FM. We first describe the nature of his difficulties, which are mainly severe phonological deficits. Employing the divided visual field paradigm with FM revealed a greater sensitivity in the right than in the left hemisphere to orthographic variables, with a significant inhibitory N effect in the left, but not right hemisphere. Such inhibition, to a lesser degree, was found among a group of adults with dyslexia but not among age-matched normal readers. We argue that enhanced sensitivity to orthographic cues is developed in some cases of dyslexia when a normal, phonology-based left hemisphere word recognition processing is not achieved. The interpretation presented here is cast in terms of differences between people with dyslexia and typical readers that originate in the atypical way in which orthographic representations are initially set up.

Evaluating a split fovea model of visual word recognition: effects of case alternation in the two visual fields and in the left and right halves of words presented at the fovea

Two experiments are reported exploring the effect of cAsE aLtErNaTiOn on lexical decisions to words and nonwords presented laterally or centrally. In line with previous research, Experiment 1 found that case alternation slowed lexical decision responses to words more in the right visual field (RVF) than in the left visual field (LVF). In Experiment 2, the words and nonwords were all presented centrally. There were three conditions, a condition in which the word and nonwords were presented in lower case letters, a condition in which the letters to the left of the central fixation were case alternated (e.g., aMbItion, mOdLants) and a condition in which the letters to the right of fixation were case alternated (e.g., collApSe, pireNtOl). Alternating the case of letters to the right of fixation slowed lexical decision responses more than alternating letter case to the left of fixation. The results provide further support for a split fovea account of visual word recognition according to which those letters of a centrally-fixated word that fall to the left of fixation are processed initially by the right cerebral hemisphere while those letters that fall to the right of fixation are processed initially by the left cerebral hemisphere, with the characteristics of the left and right hemispheres being revealed in the processing of initial and final letters in centrally presented words.

Why word length only matters in the left visual field

During visual word recognition, string length affects performance when stimuli are presented to the left visual field (LVF), but not when they are presented to the right visual field (RVF). Using a lexical-decision experiment, we investigated an account of this phenomenon based on the SERIOL model of letter-position encoding. Bottom-up activation patterns were adjusted via positional manipulations of letter contrast. This manipulation eliminated the LVF length effect by facilitating responses to longer words, thereby demonstrating that a length effect is not an inherent property of right-hemisphere processing. In contrast, the same manipulation slowed responses to longer words in the RVF, creating a length effect. These results show that hemisphere-specific activation patterns are the source of the asymmetry of the length effect.

A magnetic stimulation examination of orthographic neighborhood effects in visual word recognition

The split-fovea theory proposes that visual word recognition is mediated by the splitting of the foveal image, with letters to the left of fixation projected to the right hemisphere (RH) and letters to the right of fixation projected to the left hemisphere (LH). We applied repetitive transcranial magnetic stimulation (rTMS) over the left and right occipital cortex during a lexical decision task to investigate the extent to which word recognition processes could be accounted for according to the split-fovea theory. Unilateral rTMS significantly impaired lexical decision latencies to centrally presented words, supporting the suggestion that foveal representation of words is split between the cerebral hemispheres rather than bilateral. Behaviorally, we showed that words that have many orthographic neighbors sharing the same initial letters ("lead neighbors") facilitated lexical decision more than words with few lead neighbors. This effect did not apply to end neighbors (orthographic neighbors sharing the same final letters). Crucially, rTMS over the RH impaired lead-, but not end-neighborhood facilitation. The results support the split-fovea theory, where the RH has primacy in representing lead neighbors of a written word.