The effects of case mixing on word recognition: evidence from a PET study

Visual motion processing in Chinese children with developmental dyslexia: An fMRI study

Dorsal stream is an important pathway for visual information transmission. As a part of the dorsal pathway, the middle temporal visual motion areas (V5/MT+) are mainly responsible for visual motion processing and the ability of visual motion processing is closely related to reading. Compared with alphabetic scripts, the visual structure of Chinese characters is more complex and there are no clear grapheme-phoneme correspondence rules. So the ability of visual analysis plays an important role in Chinese character processing. This study first investigated the brain activation of Chinese dyslexic children and children of the same chronological age when they observed coherent motion stimuli. ROI analysis indicated that only the activation of left V5/MT+ was significantly weaker in dyslexics than that in the control group. The activity of the magnocellular-dorsal stream was closely related to orthographic awareness in the combined data (two groups) and the typical children. In dyslexia group, the stronger the activation of V5/MT+ was, the worse the phonological awareness, rapid naming performance and orthographic awareness were. In short, Chinese dyslexic children were deficient in the activation of the left V5/MT+ and the activity of the magnocellular-dorsal pathway was closely related to orthographic awareness in Chinese pupils.

How visual attention span and phonological skills contribute to N170 print tuning: An EEG study in French dyslexic students

Developmental dyslexia is a disorder characterized by a sustainable learning deficit in reading. Based on ERP-driven approaches focusing on the visual word form area, electrophysiological studies have pointed a lack of visual expertise for written word recognition in dyslexic readers by contrasting the left-lateralized N170 amplitudes elicited by alphabetic versus non-alphabetic stimuli. Here, we investigated in 22 dyslexic participants and 22 age-matched control subjects how two behavioural abilities potentially affected in dyslexic readers (phonological and visual attention skills) contributed to the N170 expertise during a word detection task. Consistent with literature, dyslexic participants exhibited poorer performance in these both abilities as compared to healthy subjects. At the brain level, we observed (1) an unexpected preservation of the N170 expertise in the dyslexic group suggesting a possible compensatory mechanism and (2) a modulation of this expertise only by phonological skills, providing evidence for the phonological mapping deficit hypothesis.

Is Sedentary Behavior Associated With Executive Function in Children and Adolescents? A Systematic Review

Background

Prolonged time on sedentary behavior, especially screen-based sitting time, is associated with unfavorable health indicators in children and adolescents. However, the effects of sedentary behavior on cognitive function remain to be elucidated.

Objective

The purpose of this systematic review was to synthesize the evidence on the associations of sedentary behavior with executive function in children and adolescents.

Methods

Four electronic databases (i.e., PubMed, Web of Science, PsycINFO, and SPORTDiscus) were searched for studies examining the associations between sedentary behavior and executive function in children and adolescents. Study quality was assessed by the NIH Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies.

Results

A total of 1,151 records were initially identified through database searches and other searches. Twelve cross-sectional and four longitudinal studies met the inclusion criteria. Of the 16 studies, seven studies found significant negative associations between sedentary behavior and executive function, and two studies presented positive associations. Eight studies measured sedentary time using accelerometers and showed varied associations between objectively measured sedentary time and executive function. Nine studies measured screen-based sedentary behavior, of which five studies found negative associations of sedentary time with executive function.

Conclusion

The available evidence on the associations between sedentary behavior and executive function is not conclusive in children and adolescents. However, screen-based sedentary behavior may be negatively associated with executive function.

The time course of processing handwritten words: An ERP investigation

Behavioral studies have shown that the legibility of handwritten script hinders visual word recognition. Furthermore, when compared with printed words, lexical effects (e.g., word-frequency effect) are magnified for less intelligible (difficult) handwriting (Barnhart and Goldinger, 2010; Perea et al., 2016). This boost has been interpreted in terms of greater influence of top-down mechanisms during visual word recognition. In the present experiment, we registered the participants' ERPs to uncover top-down processing effects on early perceptual encoding. Participants' behavioral and EEG responses were recorded to high- and low-frequency words that varied in script's legibility (printed, easy handwritten, difficult handwritten) in a lexical decision experiment. Behavioral results replicated previous findings: word-frequency effects were larger in difficult handwriting than in easy handwritten or printed conditions. Critically, the ERP data showed an early effect of word-frequency in the N170 that was restricted to the difficult-to-read handwritten condition. These results are interpreted in terms of increased attentional deployment when the bottom-up signal is weak (difficult handwritten stimuli). This attentional boost would enhance top-down effects (e.g., lexical effects) in the early stages of visual word processing.

Case mixing impedes early lexical access: converging evidence from the masked priming paradigm

When letters are presented in mixed case (e.g., "PlAnE), word recognition is slowed. This case-mixing effect has been used to argue that early stages of word recognition operate holistically (on the entire visual word form) rather than merely letter-by-letter. Contrary to this holistic view, however, a masked priming study (Perea, Vergara-Martínez, & Gomez, Cognition 142:39-43, 2015) with Spanish words argued that case mixing has no effect on early stages of visual word recognition. Their participants made lexical decisions on an uppercase target (e.g., "PLANE") preceded by an identical prime (e.g., "plane") or an unrelated prime (e.g., "music"), presented in lowercase or mixed case. Because priming effects (unrelated-identical) were unaffected by case mixing, they concluded that case mixing does not impede early lexical access. We examined whether this finding applies to English words, while also including lowercase targets to prevent a strong bias against holistic word recognition. We found larger priming effects from lowercase primes than mixed-case primes regardless of target case (lowercase vs. uppercase) and whether target case was varied within blocks (Experiment 1) or between blocks (Experiment 2). Contrary to Perea et al.'s findings for Spanish, our results suggest an early locus for the case-mixing effect, consistent with the holistic view of word recognition.

An fMRI study of English and Spanish word reading in bilingual adults

Reading relies on a left-lateralized brain system, including occipito-temporal (OTC), temporo-parietal, and inferior frontal (IFC) cortices. Neuroimaging studies have investigated whether activation in these cortices is modulated by a language's orthographic depth (consistency of grapheme-to-phoneme conversion). In Spanish-English bilinguals, some but not all studies have reported activation differences between the two languages during reading. Here, we studied Spanish-English early bilingual adults living in the United States (N = 25; 17 females, 8 males). We examined local activity, functional connectivity, and spatially distributed activity patterns during English and Spanish word reading. We found overlap in local activity for the two languages in the left IFC, but no differences in activation between them and few differences in functional connectivity (none of which were in pairs of regions known to be involved in reading); yet, there were spatially distributed patterns of brain activity that differentiate English and Spanish in regions of bilateral cerebellum/left OTC, the left superior occipital gyrus, the left IFC, and the left medial frontal gyrus. Overall, we found no evidence for differences in local activation or functional connectivity during English versus Spanish word processing in regions known to be involved in reading, yet we found brain-based evidence that Spanish-English bilinguals distinguish between the two languages.

Steady state visual evoked potentials in reading aloud: Effects of lexicality, frequency and orthographic familiarity

The present study explored the possibility to use Steady-State Visual Evoked Potentials (SSVEPs) as a tool to investigate the core mechanisms in visual word recognition. In particular, we investigated three benchmark effects of reading aloud: lexicality (words vs. pseudowords), frequency (high-frequency vs. low-frequency words), and orthographic familiarity ('familiar' versus 'unfamiliar' pseudowords). We found that words and pseudowords elicited robust SSVEPs. Words showed larger SSVEPs than pseudowords and high-frequency words showed larger SSVEPs than low-frequency words. SSVEPs were not sensitive to orthographic familiarity. We further localized the neural generators of the SSVEP effects. The lexicality effect was located in areas associated with early level of visual processing, i.e. in the right occipital lobe and in the right precuneus. Pseudowords produced more activation than words in left sensorimotor areas, rolandic operculum, insula, supramarginal gyrus and in the right temporal gyrus. These areas are devoted to speech processing and/or spelling-to-sound conversion. The frequency effect involved the left temporal pole and orbitofrontal cortex, areas previously implicated in semantic processing and stimulus-response associations respectively, and the right postcentral and parietal inferior gyri, possibly indicating the involvement of the right attentional network.

Reprint of: Visual processing of words in a patient with visual form agnosia: A behavioural and fMRI study

Patient D.F. has a profound and enduring visual form agnosia due to a carbon monoxide poisoning episode suffered in 1988. Her inability to distinguish simple geometric shapes or single alphanumeric characters can be attributed to a bilateral loss of cortical area LO, a loss that has been well established through structural and functional fMRI. Yet despite this severe perceptual deficit, D.F. is able to "guess" remarkably well the identity of whole words. This paradoxical finding, which we were able to replicate more than 20 years following her initial testing, raises the question as to whether D.F. has retained specialized brain circuitry for word recognition that is able to function to some degree without the benefit of inputs from area LO. We used fMRI to investigate this, and found regions in the left fusiform gyrus, left inferior frontal gyrus, and left middle temporal cortex that responded selectively to words. A group of healthy control subjects showed similar activations. The left fusiform activations appear to coincide with the area commonly named the visual word form area (VWFA) in studies of healthy individuals, and appear to be quite separate from the fusiform face area (FFA). We hypothesize that there is a route to this area that lies outside area LO, and which remains relatively unscathed in D.F.

Individual differences in involvement of the visual object recognition system during visual word recognition

Individuals with dyslexia often evince reduced activation during reading in left hemisphere (LH) language regions. This can be observed along with increased activation in the right hemisphere (RH), especially in areas associated with object recognition - a pattern referred to as RH compensation. The mechanisms of RH compensation are relatively unclear. We hypothesize that RH compensation occurs when the RH object recognition system is called upon to supplement an underperforming LH visual word form recognition system. We tested this by collecting ERPs while participants with a range of reading abilities viewed words, objects, and word/object ambiguous items (e.g., "SMILE" shaped like a smile). Less experienced readers differentiate words, objects, and ambiguous items less strongly, especially over the RH. We suggest that this lack of differentiation may have negative consequences for dyslexic individuals demonstrating RH compensation.

Resolving the locus of cAsE aLtErNaTiOn effects in visual word recognition: Evidence from masked priming

Determining the factors that modulate the early access of abstract lexical representations is imperative for the formulation of a comprehensive neural account of visual-word identification. There is a current debate on whether the effects of case alternation (e.g., tRaIn vs. train) have an early or late locus in the word-processing stream. Here we report a lexical decision experiment using a technique that taps the early stages of visual-word recognition (i.e., masked priming). In the design, uppercase targets could be preceded by an identity/unrelated prime that could be in lowercase or alternating case (e.g., table-TABLE vs. crash-TABLE; tAbLe-TABLE vs. cRaSh-TABLE). Results revealed that the lowercase and alternating case primes were equally effective at producing an identity priming effect. This finding demonstrates that case alternation does not hinder the initial access to the abstract lexical representations during visual-word recognition.

Inferior parietal lobule contributions to visual word recognition

This study investigated how the left inferior parietal lobule (IPL) contributes to visual word recognition. We used repetitive TMS to temporarily disrupt neural information processing in two anatomical fields of the IPL, namely, the angular (ANG) and supramarginal (SMG) gyri, and observed the effects on reading tasks that focused attention on either the meaning or sounds of written words. Relative to no TMS, stimulation of the left ANG selectively slowed responses in the meaning, but not sound, task, whereas stimulation of the left SMG affected responses in the sound, but not meaning, task. These results demonstrate that ANG and SMG doubly dissociate in their contributions to visual word recognition. We suggest that this functional division of labor may be understood in terms of the distinct patterns of cortico-cortical connectivity resulting in separable functional circuits.

Visual processing of multiple elements in the dyslexic brain: evidence for a superior parietal dysfunction

The visual attention (VA) span deficit hypothesis of developmental dyslexia posits that impaired multiple element processing can be responsible for poor reading outcomes. In VA span impaired dyslexic children, poor performance on letter report tasks is associated with reduced parietal activations for multiple letter processing. While this hints towards a non-specific, attention-based dysfunction, it is still unclear whether reduced parietal activity generalizes to other types of stimuli. Furthermore, putative links between reduced parietal activity and reduced ventral occipito-temporal (vOT) in dyslexia have yet to be explored. Using functional magnetic resonance imaging, we measured brain activity in 12 VA span impaired dyslexic adults and 12 adult skilled readers while they carried out a categorization task on single or multiple alphanumeric or non-alphanumeric characters. While healthy readers activated parietal areas more strongly for multiple than single element processing (right-sided for alphanumeric and bilateral for non-alphanumeric), similar stronger multiple element right parietal activations were absent for dyslexic participants. Contrasts between skilled and dyslexic readers revealed significantly reduced right superior parietal lobule (SPL) activity for dyslexic readers regardless of stimuli type. Using a priori anatomically defined regions of interest, we showed that neural activity was reduced for dyslexic participants in both SPL and vOT bilaterally. Finally, we used multiple regressions to test whether SPL activity was related to vOT activity in each group. In the left hemisphere, SPL activity covaried with vOT activity for both normal and dyslexic readers. In contrast, in the right hemisphere, SPL activity covaried with vOT activity only for dyslexic readers. These results bring critical support to the VA interpretation of the VA Span deficit. In addition, they offer a new insight on how deficits in automatic vOT based word recognition could arise in developmental dyslexia.

Failure to learn a new spatial format in children with developmental dyslexia

A general problem in studying children with developmental dyslexia is how to separate inefficiency in learning on the one hand from exposure to written texts on the other. To evaluate dyslexic children's learning abilities with graphemic materials, we tested their improvement in a condition that minimized previous experience with words (i.e., “novel words”) and with the standard, horizontal spatial letter array (i.e., a non-canonical “zigzag” format). We selected five pairs of children with dyslexia and (younger) typically developing readers matched for reading speed and accuracy in these specific conditions. Reading performance on novel words in the zigzag format was measured in 23 sessions; learning curves were fitted by power functions. Similar to typically developing readers, children with dyslexia improved their reading of novel words presented in the new format; however, their rate of learning was slower than that of typically developing readers. Furthermore, their learning to read in the new format did not generalize to novel untrained items, whereas significant generalization was present in typically developing readers. As the failure to generalize learning of the spatial format could not be attributed to reduced experience, it indicates a genuine disability and points to impaired perceptual learning as a factor in developmental dyslexia.

The Role of the Right Posterior Parietal Cortex in Letter Migration between Words

When briefly presented with pairs of words, skilled readers can sometimes report words with migrated letters (e.g., they report hunt when presented with the words hint and hurt). This and other letter migration phenomena have been often used to investigate factors that influence reading such as letter position coding. However, the neural basis of letter migration is poorly understood. Previous evidence has implicated the right posterior parietal cortex (PPC) in processing visuospatial attributes and lexical properties during word reading. The aim of this study was to assess this putative role by combining an inhibitory TMS protocol with a letter migration paradigm, which was designed to examine the contributions of visuospatial attributes and lexical factors. Temporary interference with the right PPC led to three specific effects on letter migration. First, the number of letter migrations was significantly increased only in the group with active stimulation (vs. a sham stimulation group or a control group without stimulation), and there was no significant effect on other error types. Second, this effect occurred only when letter migration could result in a meaningful word (migration vs. control context). Third, the effect of active stimulation on the number of letter migrations was lateralized to target words presented on the left. Our study thus demonstrates that the right PPC plays a specific and causal role in the phenomenon of letter migration. The nature of this role cannot be explained solely in terms of visuospatial attention, rather it involves an interplay between visuospatial attentional and word reading-specific factors.

The visual representations of words and style in text: an adaptation study

While the nature of face representations in the human perceptual system has been extensively studied using adaptation, there has been little investigation using this technique of the neural basis of another parallel class of high-level objects, words. We used the perceptual-bias technique to determine if aftereffects could be generated for either the word content or stylistic properties of textual stimuli, and if these aftereffects showed invariance for the non-adapted dimension. In a first experiment, we examined adaptation for word versus handwriting style. In a second experiment we contrasted adaptation for words with adaptation for computer font. The third experiment performed a similar study of aftereffects for words and case. In all three experiments we consistently found adaptation for words, which were not diminished by changing the style between the adapting and probe stimuli: hence word aftereffects are invariant for handwriting, font and case. Aftereffects were negligible for style. Additional analyses showed that discriminative ability was better for word than for style content. These results confirm that the neural representations of words can be probed with the adaptation technique and suggest that adaptation accesses word representations at an abstract level, where the identity of a word is invariant for stylistic properties.

Reading without the left ventral occipito-temporal cortex

The left ventral occipito-temporal cortex (LvOT) is thought to be essential for the rapid parallel letter processing that is required for skilled reading. Here we investigate whether rapid written word identification in skilled readers can be supported by neural pathways that do not involve LvOT. Hypotheses were derived from a stroke patient who acquired dyslexia following extensive LvOT damage. The patient followed a reading trajectory typical of that associated with pure alexia, re-gaining the ability to read aloud many words with declining performance as the length of words increased. Using functional MRI and dynamic causal modelling (DCM), we found that, when short (three to five letter) familiar words were read successfully, visual inputs to the patient’s occipital cortex were connected to left motor and premotor regions via activity in a central part of the left superior temporal sulcus (STS). The patient analysis therefore implied a left hemisphere “reading-without-LvOT” pathway that involved STS. We then investigated whether the same reading-without-LvOT pathway could be identified in 29 skilled readers and whether there was inter-subject variability in the degree to which skilled reading engaged LvOT. We found that functional connectivity in the reading-without-LvOT pathway was strongest in individuals who had the weakest functional connectivity in the LvOT pathway. This observation validates the findings of our patient’s case study. Our findings highlight the contribution of a left hemisphere reading pathway that is activated during the rapid identification of short familiar written words, particularly when LvOT is not involved. Preservation and use of this pathway may explain how patients are still able to read short words accurately when LvOT has been damaged.

A review and synthesis of the first 20 years of PET and fMRI studies of heard speech, spoken language and reading

The anatomy of language has been investigated with PET or fMRI for more than 20 years. Here I attempt to provide an overview of the brain areas associated with heard speech, speech production and reading. The conclusions of many hundreds of studies were considered, grouped according to the type of processing, and reported in the order that they were published. Many findings have been replicated time and time again leading to some consistent and undisputable conclusions. These are summarised in an anatomical model that indicates the location of the language areas and the most consistent functions that have been assigned to them. The implications for cognitive models of language processing are also considered. In particular, a distinction can be made between processes that are localized to specific structures (e.g. sensory and motor processing) and processes where specialisation arises in the distributed pattern of activation over many different areas that each participate in multiple functions. For example, phonological processing of heard speech is supported by the functional integration of auditory processing and articulation; and orthographic processing is supported by the functional integration of visual processing, articulation and semantics. Future studies will undoubtedly be able to improve the spatial precision with which functional regions can be dissociated but the greatest challenge will be to understand how different brain regions interact with one another in their attempts to comprehend and produce language.

The role of the ventral and dorsal pathways in reading Chinese characters and English words

Previous literature in alphabetic languages suggests that the occipital-temporal region (the ventral pathway) is specialized for automatic parallel word recognition, whereas the parietal region (the dorsal pathway) is specialized for serial letter-by-letter reading (Cohen et al., 2008; Ho et al., 2002). However, few studies have directly examined the role of the ventral and dorsal pathways in Chinese reading compared to English reading. To investigate this issue, we adopted the degraded word processing paradigm used by Cohen et al. (2008) and compared brain regions involved in the processing of degraded Chinese characters and English words during lexical decision, using functional magnetic resonance imaging (fMRI). The degraded characters/words were created by inserting blank spaces between radicals of Chinese characters or syllables of English polysyllabic words. Generally, the current study replicated the effects of Cohen et al. (2008), showing that in Chinese - like in alphabetic languages - character spacing modulates both ventral (bilateral cuneus, left middle occipital gyrus) and dorsal (left superior parietal lobule and middle frontal gyrus) pathways. In addition, the current study showed greater activation in bilateral cuneus and right lingual gyrus for Chinese versus English when comparing spaced to normal stimuli, suggesting that Chinese character recognition relies more on ventral visual-spatial processing than English word recognition. Interestingly, bilateral cuneus showed monotonic patterns in response to increasing spacing, while the rest of the regions of interest showed non-monotonic patterns, indicating different profiles for these regions in visual-spatial processing.

The putative visual word form area is functionally connected to the dorsal attention network

The putative visual word form area (pVWFA) is the most consistently activated region in single word reading studies (i.e., Vigneau et al. 2006), yet its function remains a matter of debate. The pVWFA may be predominantly used in reading or it could be a more general visual processor used in reading but also in other visual tasks. Here, resting-state functional connectivity magnetic resonance imaging (rs-fcMRI) is used to characterize the functional relationships of the pVWFA to help adjudicate between these possibilities. rs-fcMRI defines relationships based on correlations in slow fluctuations of blood oxygen level-dependent activity occurring at rest. In this study, rs-fcMRI correlations show little relationship between the pVWFA and reading-related regions but a strong relationship between the pVWFA and dorsal attention regions thought to be related to spatial and feature attention. The rs-fcMRI correlations between the pVWFA and regions of the dorsal attention network increase with age and reading skill, while the correlations between the pVWFA and reading-related regions do not. These results argue the pVWFA is not used predominantly in reading but is a more general visual processor used in other visual tasks, as well as reading.

Encoding in the Visual Word Form Area: An fMRI Adaptation Study of Words versus Handwriting

Written texts are not just words but complex multidimensional stimuli, including aspects such as case, font, and handwriting style, for example. Neuropsychological reports suggest that left fusiform lesions can impair the reading of text for word (lexical) content, being associated with alexia, whereas right-sided lesions may impair handwriting recognition. We used fMRI adaptation in 13 healthy participants to determine if repetition–suppression occurred for words but not handwriting in the left visual word form area (VWFA) and the reverse in the right fusiform gyrus. Contrary to these expectations, we found adaptation for handwriting but not for words in both the left VWFA and the right VWFA homologue. A trend to adaptation for words but not handwriting was seen only in the left middle temporal gyrus. An analysis of anterior and posterior subdivisions of the left VWFA also failed to show any adaptation for words. We conclude that the right and the left fusiform gyri show similar patterns of adaptation for handwriting, consistent with a predominantly perceptual contribution to text processing.

Word learning and the cerebral hemispheres: from serial to parallel processing of written words

Reading familiar words differs from reading unfamiliar non-words in two ways. First, word reading is faster and more accurate than reading of unfamiliar non-words. Second, effects of letter length are reduced for words, particularly when they are presented in the right visual field in familiar formats. Two experiments are reported in which right-handed participants read aloud non-words presented briefly in their left and right visual fields before and after training on those items. The non-words were interleaved with familiar words in the naming tests. Before training, naming was slow and error prone, with marked effects of length in both visual fields. After training, fewer errors were made, naming was faster, and the effect of length was much reduced in the right visual field compared with the left. We propose that word learning creates orthographic word forms in the mid-fusiform gyrus of the left cerebral hemisphere. Those word forms allow words to access their phonological and semantic representations on a lexical basis. But orthographic word forms also interact with more posterior letter recognition systems in the middle/inferior occipital gyri, inducing more parallel processing of right visual field words than is possible for any left visual field stimulus, or for unfamiliar non-words presented in the right visual field.

Neural dynamics of reading morphologically complex words

Despite considerable research interest, it is still an open issue as to how morphologically complex words such as "car+s" are represented and processed in the brain. We studied the neural correlates of the processing of inflected nouns in the morphologically rich Finnish language. Previous behavioral studies in Finnish have yielded a robust inflectional processing cost, i.e., inflected words are harder to recognize than otherwise matched morphologically simple words. Theoretically this effect could stem either from decomposition of inflected words into a stem and a suffix at input level and/or from subsequent recombination at the semantic-syntactic level to arrive at an interpretation of the word. To shed light on this issue, we used magnetoencephalography to reveal the time course and localization of neural effects of morphological structure and frequency of written words. Ten subjects silently read high- and low-frequency Finnish words in inflected and monomorphemic form. Morphological complexity was accompanied by stronger and longer-lasting activation of the left superior temporal cortex from 200 ms onwards. Earlier effects of morphology were not found, supporting the view that the well-established behavioral processing cost for inflected words stems from the semantic-syntactic level rather than from early decomposition. Since the effect of morphology was detected throughout the range of word frequencies employed, the majority of inflected Finnish words appears to be represented in decomposed form and only very high-frequency inflected words may acquire full-form representations.

Early involvement of dorsal and ventral pathways in visual word recognition: an ERP study

Visual expertise underlying reading is attributed to processes involving the left ventral visual pathway. However, converging evidence suggests that the dorsal visual pathway is also involved in early levels of visual word processing, especially when words are presented in unfamiliar visual formats. In the present study, event-related potentials (ERPs) were used to investigate the time course of the early engagement of the ventral and dorsal pathways during processing of orthographic stimuli (high and low frequency words, pseudowords and consonant strings) by manipulating visual format (familiar horizontal vs. unfamiliar vertical format). While early ERP components (P1 and N1) already distinguished between formats, the effect of stimulus type emerged at the latency of the N2 component (225-275 ms). The N2 scalp topography and sLORETA source localisation for this differentiation showed an occipito-temporal negativity for the horizontal format and a negativity that extended towards the dorsal regions for the vertical format. In a later time window (350-425 ms) ERPs elicited by vertically displayed stimuli distinguished words from pseudowords in the ventral area, as confirmed by source localisation. The sustained contribution of occipito-temporal processes for vertical stimuli suggests that the ventral pathway is essential for lexical access. Parietal regions appear to be involved when a serial mechanism of visual attention is required to shift attention from one letter to another. The two pathways cooperate during visual word recognition and processing in these pathways should not be considered as alternative but as complementary elements of reading.

On the functional neuroanatomy of visual word processing: effects of case and letter deviance

This functional magnetic resonance imaging study contrasted case-deviant and letter-deviant forms with familiar forms of the same phonological words (e.g., TaXi and Taksi vs Taxi) and found that both types of deviance led to increased activation in a left occipito-temporal regions, corresponding to the visual word form area (VWFA). The sensitivity of the VWFA to both types of deviance may suggest that this region represents well-known visual words not only as sequences of abstract letter identities but also includes information on the typical case-format pattern of visual words. Case-deviant items, in addition to increased activation in a right occipito-temporal region and in a left occipital and a left posterior occipito-temporal region, which may reflect increased demands on the letter processing posed by the case-deviant forms.

Visual deficits in developmental dyslexia: relationships between non-linguistic visual tasks and their contribution to components of reading

Developmental dyslexia is often characterized by a visual deficit, but the nature of this impairment and how it relates to reading ability is disputed (Brain 2003; 126: 841-865). In order to investigate this issue, we compared groups of adults with and without dyslexia on the Ternus, visual-search and symbols tasks. Dyslexic readers yielded more errors on the visual-search and symbols tasks compared with non-dyslexic readers. A positive correlation between visual-search and symbols task performance suggests a common mechanism shared by these tasks. Performance on the visual-search and symbols tasks also correlated with non-word reading and rapid automatized naming measures, and visual search contributed independent variance to non-word reading. The Ternus task did not discriminate reading groups nor contributed significant variance to reading measures. We consider how visual-attention processes might underlie specific component reading measures.

Using spatial frequency adaptation to study word recognition

The study of spatial frequency is being used increasingly often to investigate processes underlying visual word recognition. However, research in this area has adopted techniques that require the physical deformation of word targets used in experiments (e.g., filtered images of words, words embedded in visual noise), and this approach may limit the inferences that can be made about the role of spatial frequencies in normal word recognition. Spatial frequency adaptation is described in this article as an additional technique for studying the role of spatial frequency information in word recognition. The advantage of this technique is that it alters participants' sensitivity to particular spatial frequencies and so allows the study of spatial frequency involvement in word recognition using normal images of word stimuli. The application of the adaptation technique to studies of word recognition is explained in detail and its potential is then demonstrated by an example word recognition experiment in which spatial frequency adaptation was used.

Abstraction and perceptual individuation in primed word identification are modulated by distortion and repetition: a dissociation

One experiment investigated the effects of distortion and multiple prime repetition (super-repetition) on repetition priming using divided-visual-field word identification at test and mixed-case words (e.g., goAT). The experiment measured form-specificity (the effect of matching lettercase at study and test) for two non-conceptual study tasks. For an ideal typeface, super-repetition increased form-independent priming leaving form-specificity constant. The opposite pattern was found for a distorted typeface; super-repetition increased form-specificity, leaving form-independent priming constant. These priming effects did not depend on the study task or test hemifield for either typeface. An additional finding was that only the ideal typeface showed the usual advantage of right hemifield presentation. These results demonstrate that super-repetition produced abstraction for the ideal typeface and perceptual individuation for the distorted typeface; abstraction and perceptual individuation dissociated. We suggest that there is a fundamental duality between perceptual individuation and abstraction consistent with Tulving's (1984) distinction between episodic and semantic memory. This could reflect a duality of system or process.

N170 ERPs could represent a logographic processing strategy in visual word recognition

BACKGROUND

Occipito-temporal N170 component represents the first step where face, object and word processing are discriminated along the ventral stream of the brain. N170 leftward asymmetry observed during reading has been often associated to prelexical orthographic visual word form activation. However, some studies reported a lexical frequency effect for this component particularly during word repetition that appears in contradiction with this prelexical orthographic step. Here, we tested the hypothesis that under word repetition condition, discrimination between words would be operated on visual rather than orthographic basis. In this case, N170 activity may correspond to a logographic processing where a word is processed as a whole.

METHODS

To test such an assumption, frequent words, infrequent words and pseudowords were presented to the subjects that had to complete a visual lexical decision task. Different repetition conditions were defined 1--weak repetition, 2--massive repetition and 3--massive repetition with font alternation. This last condition was designed to change visual word shape during repetition and therefore to interfere with a possible visual strategy during word recognition.

RESULTS

Behavioral data showed an important frequency effect for the weak repetition condition, a lower but significant frequency effect for massive repetition, and no frequency effect for the changing font repetition. Moreover alternating font repetitions slowed subject's responses in comparison to "simple" massive repetition.ERPs results evidenced larger N170 amplitude in the left hemisphere for frequent than both infrequent words and pseudowords during massive repetition. Moreover, when words were repeated with different fonts this N170 effect was not present, suggesting a visual locus for such a N170 frequency effect.

CONCLUSION

N170 represents an important step in visual word recognition, consisting probably in a prelexical orthographic processing. But during the reading of very frequent words or after a massive repetition of a word, it could represent a more holistic process where words are processed as a global visual pattern.

"What" and "where" in word reading: ventral coding of written words revealed by parietal atrophy

The visual system of literate adults develops a remarkable perceptual expertise for printed words. To delineate the aspects of this competence intrinsic to the occipitotemporal "what" pathway, we studied a patient with bilateral lesions of the occipitoparietal "where" pathway. Depending on critical geometric features of the display (rotation angle, letter spacing, mirror reversal, etc.), she switched from a good performance, when her intact ventral pathway was sufficient to encode words, to severely impaired reading, when her parietal lesions prevented the use of alternative reading strategies as a result of spatial and attentional impairments. In particular, reading was disrupted (a) by rotating word by more than 50 degrees , providing an approximation of the invariance range for words encoding in the ventral pathway; (b) by separating letters with double spaces, revealing the limits of letter grouping into perceptual wholes; (c) by mirror-reversing words, showing that words escape the default mirror-invariant representation of visual objects in the ventral pathway. Moreover, because of her parietal lesions, she was unable to discriminate mirror images of common objects, although she was excellent with reversible pseudowords, confirming that the breaking of mirror symmetry was intrinsic to the occipitotemporal cortex. Thus, charting the display conditions associated with preserved or impaired performance allowed us to infer properties of word coding in the normal ventral pathway and to delineate the roles of the parietal lobes in single-word recognition.

A selective effect of parietal damage on letter identification in mixed case words

We investigated the reading of cAsE mIxInG and contrast reduction on word reading in patients with unilateral parietal lesions and attentional deficits. We show that, compared with control participants, the patients produce selective increases in lateralised errors when reading mixed case relative to same case words. However, there were not reliable increases in lateralised errors when words were degraded by low contrast. The patients also showed some increases in contralesional errors at a task aimed at feature processing in words (a gap detection task), but these effects were not increased for mixed case stimuli and errors were reduced relative to the word reading task. The results are consistent with mixed case words stressing attention-demanding letter identification, drawing-out an impairment in the patients in attending to contralesional stimuli. On the other hand, effects of contrast reduction are accommodated without necessarily recruiting attentional processes mediated by the posterior parietal lobe.

Examining the word identification stages hypothesized by the E-Z Reader model

A critical prediction of the E-Z Reader model is that experimental manipulations that disrupt early encoding of visual and orthographic features of the fixated word without affecting subsequent lexical processing should influence the processing difficulty of the fixated word without affecting the processing of the next word. We tested this prediction by monitoring participants' eye movements while they read sentences in which a target word was presented either normally or altered. In the critical condition, the contrast between the target word and the background was substantially reduced. Such a reduction in stimulus quality is typically assumed to have an impact that is largely confined to a very early stage of word recognition. Results were consistent with the E-Z Reader model: This faint presentation had a robust influence on the duration of fixations on the target word without substantially altering the processing of the next word.

The “Special Effect” of Case Mixing on Word Identification: Neuropsychological and Transcranial Magnetic Stimulation Studies Dissociating Case Mixing from Contrast Reduction

We present neuropsychological and transcranial magnetic stimulation (TMS) evidence with normal readers, that the effects of case mixing and contrast reduction on word identification are qualitatively different. Lesions and TMS applied to the right parietal lobe selectively disrupted the identification of mixed relative to single-case stimuli. Bilateral lesions and TMS applied to the occipital cortex selectively disrupted the identification of low-contrast words. These data suggest that different visual distortions (case mixing, contrast reduction) exert different effects on reading, modulated by contrasting brain regions. Case mixing is a “special” distortion and involves the recruitment of processes that are functionally distinct, and dependent on different regions in the brain, from those required to deal with contrast reduction.

Attentional shifting and the role of the dorsal pathway in visual word recognition

A substantial amount of evidence has been collected to propose an exclusive role for the dorsal visual pathway in the control of guided visual search mechanisms, specifically in the preattentive direction of spatial selection [Vidyasagar, T. R. (1999). A neuronal model of attentional spotlight: Parietal guiding the temporal. Brain Research and Reviews, 30, 66-76; Vidyasagar, T. R. (2001). From attentional gating in macaque primary visual cortex to dyslexia in humans. Progress in Brain Research, 134, 297-312]. Moreover, it has been suggested recently that the dorsal visual pathway is specifically involved in the spatial selection and sequencing required for orthographic processing in visual word recognition. In this experiment we manipulate the demands for spatial processing in a word recognition, lexical decision task by presenting target words in a normal spatial configuration, or where the constituent letters of each word are spatially shifted relative to each other. Accurate word recognition in the Shifted-words condition should demand higher spatial encoding requirements, thereby making greater demands on the dorsal visual stream. Magnetoencephalographic (MEG) neuroimaging revealed a high frequency (35-40Hz) right posterior parietal activation consistent with dorsal stream involvement occurring between 100 and 300ms post-stimulus onset, and then again at 200-400ms. Moreover, this signal was stronger in the shifted word condition, compared to the normal word condition. This result provides neurophysiological evidence that the dorsal visual stream may play an important role in visual word recognition and reading. These results further provide a plausible link between early stage theories of reading, and the magnocellular-deficit theory of dyslexia, which characterises many types of reading difficulty.

The effect of visual word features on the acquisition of orthographic knowledge

Research with adults has shown that the distortion of visual word features, and in particular of the multiletter features within words, hampers word recognition. In this study, "CaSe MiXiNg" was employed to examine the effect of disrupting visual word features on the acquisition of orthographic knowledge in children. During the training, 18 beginning and 27 advanced readers (in Grades 2, 4, and 5) repeatedly read a set of pseudowords in either lowercase or mixed case. During this training, case mixing appeared to impair reading speed in both reader groups. At posttest, 1 day after the training, case format was either the same as or different from that during the training. Lowercase pseudowords were recognized faster after a lowercase training than after a mixed-case training. In a second study, case was found not to affect the rapid naming of single letters. The combined results suggest that case mixing disrupted the multiletter features in pseudowords and that the disruption of these features can affect the acquisition of orthographic knowledge.

Word and non-word reading: What role for the Visual Word Form Area?

The putative role of the so-called Visual Word Form Area (VWFA) during reading remains under debate. For some authors, this region is specifically involved in a pre-lexical processing of words and pseudowords, whereas such specificity is challenged by others given the VWFA involvement during both non-word reading and word listening. Here, we further investigated this issue, measuring BOLD variations and their lateralization with fMRI during word and non-word reading, in order to evaluate the lexicality effect, and during reading and listening of words, in order to evaluate the impact of stimulus delivery modality on word processing networks. Region of interest (ROI) analysis was first performed in three target areas: 1-VWFA as defined by a meta-analysis of the word reading literature, 2-a middle temporal area (T2) found co-activated by both word reading and listening, 3-an inferior occipital area (OI) belonging to the unimodal visual cortex of the inferior occipital gyrus. VWFA activity was found not different between word and non-word reading but was more leftward lateralized during word reading due to a reduction of activity in the VWFA right counterpart. A similar larger leftward lateralization during word reading was also uncovered in the T2 ROI but was related to a larger left side activity. Such a lexicality effect was not observed in the OI ROI. By contrast, BOLD increases during listening were restricted to the left VWFA and T2 ROIs. Voxel-based analysis (SPM99) showed that semantic areas were more active during word than non-word reading and co-activated by both reading and listening, exhibiting a left lateralized activity in all tasks. These results indicate that the left VWFA would be the place where visual and verbal representations bind under the control of left semantic areas.

Case mixing and the right parietal cortex: evidence from rTMS

We investigated the necessary role of the right parietal lobe in visual word recognition using transcranial magnetic stimulation (TMS). TMS was applied to the right posterior parietal lobe and to a control area as participants read aloud words presented either in lower case or in mIxEd-cAsE. The words were presented either with unlimited duration and high contrast (Experiment 1), or with brief presentation and low-contrast (Experiments 2 and 3). In all three experiments, TMS over the parietal area disrupted reading, and in Experiments 2 and 3 this effect was most pronounced for mIxEd-cAsE words. This suggests that the right parietal lobe mediates the recognition of words in unfamiliar formats.

Reading in a regular orthography: an FMRI study investigating the role of visual familiarity

In order to separate the cognitive processes associated with phonological encoding and the use of a visual word form lexicon in reading, it is desirable to compare the processing of words presented in a visually familiar form with words in a visually unfamiliar form. Japanese Kana orthography offers this possibility. Two phonologically equivalent but visually dissimilar syllabaries allow the writing of, for example, foreign loanwords in two ways, only one of which is visually familiar. Familiarly written words, unfamiliarly written words, and pseudowords were presented in both Kana syllabaries (yielding six conditions in total) to participants during an fMRI measurement with a silent articulation task (Experiment 1) and a phonological lexical decision task (Experiment 2) using an event-related design. Consistent over two experimental tasks, the three different stimulus types (familiar, unfamiliar, and pseudoword) were found to activate selectively different brain regions previously associated with phonological encoding and word retrieval or meaning. Compatible with the predictions of the dual-route model for reading, pseudowords and visually unfamiliar words, which have to be read using phonological assembly, caused an increase in brain activity in left inferior frontal regions (BA 44/47), as compared to visually familiar words. Visually familiar and unfamiliar words were found to activate a range of areas associated with lexico-semantic processing more strongly than pseudowords, such as the left and right temporo-parietal region (BA 39/40), a region in the left middle/inferior temporal gyrus (BA 20/21), and the posterior cingulate (BA 31).

Number-word reading as challenging task in dyslexia? An ERP study

The aim of the present study was to evaluate processes of lexical access, selection and early semantic access in young native Hungarian students as well as in dyslexics compensating successfully for their reading problems of developmental origin. The present study made use of the well-known lexical decision paradigm in which event-related potentials (ERPs) elicited by words, number-words and pseudowords were measured. Subjects had to judge whether the letter strings seen were meaningful or meaningless. Our results suggest that in good readers additional activity occurs in the sensory or selection stage of lexical access when words of low sight frequency, e.g. number-words are read. Significant processing differences for words vs. number-words were found in the later stage of processing. Based on our ERP data we do not suggest number-words for judging general features of lexical processing, especially when developmental dyslexia is the focus of study. Our results show that young adults may develop a particular compensation strategy for reading words of different frequency. We found that: (1) Lexical access is fast and accurate in good readers and the early components elicited by words and number-words do not differ. (2) Attentional effort is reflected by enhanced early components to number-words. (3) Dyslexics may compensate for the weakness of sight word vocabulary, characteristic for frequent words as well, during lexical selection and at a later stage of processing. (4) Dyslexic adults, who compensate well for reading difficulties, differ significantly in this later stage when words have to be read. (5) The late positive component of ERPs reflects additional activation allocated to word reading when low frequency words such as number-words are read. Good readers show this effect as well, therefore, the largest difference found between dyslexics and controls is found for frequent words. (6) The early semantic access is absent in dyslexics when pseudowords are read and this process may be one of the strategies used by dyslexics in a transparent orthography.

A case for case: handling letter case selection in written spelling

This study reports the unusual writing performance of a 72-year-old woman, Pp, who was unable to maintain her writing within a particular case, and made numerous case mixing errors (e.g. insTEAd). Her oral spelling was flawless, but when tested using a written spelling task (including words and non-words), a picture description task, a sentence writing task and a transcription task (from upper case to lower case, and vice versa), she showed a high proportion of case mixing errors, though spelling per se was correct. The problem, although less severe, was also present when spelling with letter cards. Despite a spared ability to select the correct letters in the stimulus, specify the correct number of letters and place them in the correct order, she had a specific problem in selecting the appropriate case. This impairment is indicative of peripheral dysgraphia. She appeared to have intact orthographic representations, but selection of the appropriate allographic codes for upper and lower case was impaired. Her longitudinal neuropsychological profile and MRI evidence suggest that Pp suffers from mild vascular dementia with more severe impairments in attentional functions. Her writing deficits may be accounted for by a model that incorporates an inhibitory mechanism, which is responsible for maintaining the appropriate case and inhibiting the inappropriate one, subsequent to case selection in writing. Failure of this mechanism would explain the pattern of case mixing shown by Pp.

Frequency effects of Chinese character processing in the brain: an event-related fMRI study

Knowing how the brain processes Chinese characters of different frequencies of occurrence may shed light on the extent to which orthographic variations of different languages can influence reading processes in the brain. In the present study, event-related fMRI was used to investigate frequency effects on Chinese character processing. Reading low-frequency characters invoked higher activation in several brain regions including the left premotor/inferior frontal gyrus, supplementary motor area, left anterior insula, left posterior inferior temporal gyrus, left superior parietal cortex, and lingual cortex, while reading high-frequency characters resulted in higher activation in the left supramarginal/angular gyrus and left precuneus. The activation pattern of reading infrequently encountered characters reflects a more demanding processing procedure of retrieving, formulating, and coordinating the phonological output. Access to the lexical route may benefit the reading of high-frequency characters. By uncovering the differential brain responses in reading Chinese characters of different occurrence frequencies, not only has a substantial overlap between functional neuroanatomy of reading Chinese and alphabetical languages been demonstrated, but also features permitting the separation of language-specific content from universal mechanisms.

Children with dyslexia and right parietal lobe dysfunction: event-related potentials in response to words and pseudowords

Hari and Renvall (Trends Cogn. Sci., 5 (2001) 525) proposed that dyslexic children suffer from sluggish attention deployment due to a right parietal lobe dysfunction. To examine this hypothesis, good and poor readers (12, 11-year-old boys in each group) had to read familiar words (low attentional demand) and pseudowords (high attentional demand). The amplitude of the event-related potential at around 100 ms post-stimulus (N1) in response to words and pseudowords was used as measure of attention deployment. Consistent with the attention deficit/right parietal lobe dysfunction hypothesis, poor readers showed lower N1 amplitudes in response to pseudowords, but not in response to words at central sites of the right hemisphere. However, poor readers also showed lower N1 amplitudes to both words and pseudowords at left frontal sites suggestive of an early deficit in activating phonological codes.