Paradoxical Enhancement of Letter Recognition in Developmental Dyslexia

Parafoveal Processing and Transposed-Letter Effects in Developmental Dyslexic Reading

During reading, adults and children independently parafoveally encode letter identity and letter position information using a flexible letter position encoding mechanism. The current study examined parafoveal encoding of letter position and letter identity for dyslexic children. Eye movements were recorded during a boundary-change paradigm. Parafoveal previews were either an identity preview (e.g., nearly), a transposed-letter preview (e.g., enarly) or a substituted-letter preview (e.g., acarly). Dyslexic readers showed a preview benefit for identity previews, indicating that orthographic information was encoded parafoveally. Furthermore, dyslexic readers benefitted from transposed-letter previews more than substituted-letters previews, demonstrating that letter identity was encoded independently to letter position during parafoveal processing. Although a transposed-letter effect was found for dyslexic readers, they demonstrated a reduced sensitivity to detect transposed-letters in later measures of reading, that is, go-past times, relative to that found for typically developing readers. We conclude that dyslexic readers, with less rich and fully specified lexical representations, have a reduced sensitivity to transpositions of the first two letters of the upcoming word in preview. These findings are compatible with the view that orthographic representations of dyslexic children are not sufficiently specified.

Letters away from the looking glass: Developmental trajectory of mirrored and rotated letter processing within words

Discrimination of reversible mirrored letters (e.g., d and b) poses a challenge when learning to read as it requires overcoming mirror invariance, an evolutionary-old perceptual tendency of processing mirror images as equivalent. The present study investigated when, in reading development, mirror-image discrimination becomes automatic during visual word recognition. The developmental trajectory of masked priming effects was investigated from 2nd to 6th grade and in adults, by manipulating letter type (nonreversible; reversible) and prime condition (control; identity; mirrored; rotated). Standardized identity priming increased along reading development. Beginning readers showed mirror invariance during reversible and nonreversible letter processing. A mirror cost (slower word recognition in mirrored-letter than identity prime condition) was found by 5th-grade but only for reversible letters. By 6th grade, orthographic processing was no longer captive of mirror invariance. A multiple linear regression showed that letter representations, but not phonological processes or age, were a reliable predictor of the rise of mirror-image discrimination in 2nd-4th-graders. The present results suggest a protracted development of automatic mirror-image discrimination during orthographic processing, contingent upon the quality of abstract letter representations. RESEARCH HIGHLIGHTS: We traced the developmental trajectory of mirrored-letter and rotated-letter priming effects (e.g., ibea and ipea as primes of IDEA) in visual word recognition. Beginning readers (2nd-4th-graders) showed mirror invariance and plane-rotation sensitivity in orthographic processing, thus still being susceptible to the perceptual biases in charge in object recognition. A mirror cost was found in 5th-graders but only for reversible letters; orthographic processing was no longer captive of mirror invariance by 6th-grade. The automation of mirror-image discrimination during orthographic processing depends on the quality of letter representations but not on phonological processes or age.

Cognitive-Motor Training Improves Reading-Related Executive Functions: A Randomized Clinical Trial Study in Dyslexia

Children with developmental dyslexia (DD) often struggle with executive function difficulties which can continue into adulthood if not addressed. This double-blinded randomized clinical trial study evaluated the short-term effects of the Verbal Working Memory-Balance (VWM-B) program on reading-related executive functions, reading skills, and reading comprehension in Persian children with DD. The active control group [12 children with DD with a mean age of 9 years (SD = 0.90)] received training using the single-task VWM program, while the experiment group [15 children with DD with a mean age of 8 years (SD = 0.74)] received training with the dual-task VWM-B program. Both groups received fifteen training sessions, and assessments were conducted before and after the intervention. The groups were homogenized for possible confounders of age, gender, IQ level, and attention level. The study employed separate mixed ANOVA analyses to estimate the impact of training programs on various measured functions. Significant improvements were observed in the outcome measures of backward digit span, text comprehension, verbal fluency, Stroop color-word test and interference, and the reading subtests. Additionally, significant correlations were found between reading skills and backward digit span, text comprehension, verbal fluency, and Stroop variables. In conclusion, the dual-task VWM-B program was found to be more effective than the single-task VWM program in improving selective attention, cognitive inhibition, verbal working memory capacity, information processing speed, naming ability, and lexical access speed. These enhanced executive functions were associated with improved reading skills in children with DD.

Preventing the Development of Dyslexia: A Reply to Mather

Because reading/writing is a fundamental tool for children's development, the main failure in its learning-developmental dyslexia-gives rise to many attempts to remediate. A recent remedy proposed by Mather (2022), published in Perceptual and Motor Skills [129(3), p. 468], is impressive through its radical nature and the extent of its consequences. It consists of delaying the teaching of writing to the age of 7-8 years, whereas, at present, most children in Western or comparable cultures learn to write even before compulsory school (generally at age six). In this article, I present a set of arguments whose addition and possible interaction lead, if not to reject, at least to restrict Mather's proposal. My arguments show both the inefficiency of Mather's proposal through two observational studies, its practical inapplicability in contemporary society, the importance of learning to write at least in the first year of elementary school, and the stinging past failure of a math reform of similar scope (i.e., learning to count). I also question the neurological theory underlying Mather's proposal, and, finally, I point out that, even if delaying learning to write were limited to students who Mather expects (at age six) to experience future dyslexia, this remedy would be inapplicable and probably ineffective.

A Scoping Review on Movement, Neurobiology and Functional Deficits in Dyslexia: Suggestions for a Three-Fold Integrated Perspective

Developmental dyslexia is a common complex neurodevelopmental disorder. Many theories and models tried to explain its symptomatology and find ways to improve poor reading abilities. The aim of this scoping review is to summarize current findings and several approaches and theories, focusing on the interconnectedness between motion, emotion and cognition and their connection to dyslexia. Consequently, we present first a brief overview of the main theories and models regarding dyslexia and its proposed neural correlates, with a particular focus on cerebellar regions and their involvement in this disorder. After examining different types of intervention programs and remedial training, we highlight the effects of a specific structured sensorimotor intervention named Quadrato Motor Training (QMT). QMT utilizes several cognitive and motor functions known to be relevant in developmental dyslexia. We introduce its potential beneficial effects on reading skills, including working memory, coordination and attention. We sum its effects ranging from behavioral to functional, structural and neuroplastic, especially in relation to dyslexia. We report several recent studies that employed this training technique with dyslexic participants, discussing the specific features that distinguish it from other training within the specific framework of the Sphere Model of Consciousness. Finally, we advocate for a new perspective on developmental dyslexia integrating motion, emotion and cognition to fully encompass this complex disorder.

Skilled readers show different serial-position effects for letter versus non-letter target detection in mixed-material strings

The study explored whether target detection in a five-character string depends on whether a letter or a non-letter was presented, as a predesignated target. Skilled readers had to identify a single letter or non-letter in a five-character string, randomly composed of letters and non-letters. It was found that an analytic processing strategy is automatically elicited if participants were instructed to detect a letter target. In this instance, a linear model best explained the RT variance for letters: with increasing RTs from left to right, suggesting a serial item-by-item reading-specific strategy comparable to alphabetic reading. For non-letters, in contrast, a symmetrical U-shaped function best explained the RT variance, suggesting a symmetrical scanning-out from the central to the terminal positions of the string. Since the design precludes orthographic and semantic influences, it can be concluded that a reading-specific strategy for alphabetic processing is automatically activated if the string is scanned for a letter-target. Thus, the pre-designated target triggers the strategy for processing the string and determines related position effects. The results suggest that effects from earlier studies, which showed an analytic processing preference for isolated letters (APPLE) in recognition tasks, as a consequence of literacy acquisition, generalize to the processing of letters in strings.

Braille readers break mirror invariance for both visual Braille and Latin letters

For this study, we started from the observation that the poor adequacy of a script to the requirements of the human visual system strongly impacts some aspects of reading expertise (e.g., fluent reading). Here we investigated another of these aspects, namely the ability to break mirror invariance, which makes it hard for readers to ignore the mirrored contrasts of letters even if this hinders performance. In particular, we hypothesized that this ability would be preserved for the visually presented letters of the Braille alphabet despite their poor fit to the constraints of the human visual system, as it did for congenital Braille readers when they explored the same letters through the tactile modality (de Heering, Collignon, & Kolinsky, 2018). To test so, we measured visual Braille readers' mirror costs, indexing for their difficulty to consider mirrored items as identical compared to strictly identical items, for three materials: Braille letters, geometrical shapes and Latin letters, which invariant properties are typically considered as having been selected through cultural evolution because they match the requirements of the visual system. Contrary to people having never experienced Braille, Braille readers' mirror cost was of the same magnitude for Latin letters and Braille letters and steadily increased the more they had experience with the latter material. Both these costs were also stronger than what was observed for geometrical shapes. Overall these results suggest that the poor adequacy of the Braille alphabet to the visual system does not impede Braille readers to break mirror invariance for the Braille material.

The mirror reflects more for d than for b: Right asymmetry bias on the visual recognition of words containing reversal letters

Research has shown that recognizing words that contain reversal letters (e.g., b/d) is more difficult than recognizing words that do not contain them. Although none of the current computational models of visual word recognition can account for this effect, it was recently suggested that it may arise from lateral inhibition connections that, at the letter level of processing, can be established between reversal nodes. However, because in writing left-faced letters (e.g., d) are more prone to be reversed into right-faced letters (e.g., b) than the inverse, we hypothesized that the directionality of the reversal letters could modulate the magnitude of the mirror-letter interference effect. In this study, we directly tested this hypothesis by using a highly controlled set of European Portuguese (EP) words containing only either the mirror-letter b or the mirror-letter d in three lexical decision (go/no-go) masked priming experiments conducted with EP adult skilled readers (Experiment 1) and two groups of EP developing readers (third-grade children [Experiment 2] and fifth-grade children [Experiment 3]). Results showed that reliable mirror-letter interference effects were observed only for d-words in both adult skilled readers and fifth-grade children, which asks for additional amendments in the current computational models of visual word recognition.

Lost in the forest? Global to local interference depends on children's reading skills

We studied the global precedence effect in primary school children with and without developmental dyslexia, using a compound figures task with familiar (Latin) or unfamiliar (Hebrew) letters. The two components of the global precedence effect were considered separately: global advantage (faster processing of global than local letters) and asymmetric interference (global distracters interfere with local targets but not vice versa). Both groups of children showed a global advantage with familiar as well as with unfamiliar letters. Children without developmental dyslexia showed asymmetric interference on familiar letters, but not on unfamiliar ones. Children with developmental dyslexia showed no asymmetric interference, neither for familiar letters nor for unfamiliar ones. The results distinguish between alternative hypothesis regarding the roles of familiarity and visual processing strategies in the compound figures task. Consequences for understanding literacy acquisition and developmental dyslexia are discussed.

Attention allows the SNARC effect to operate on multiple number lines

To investigate whether participants can activate only one spatially oriented number line at a time or multiple number lines simultaneously, they were asked to solve a unit magnitude comparison task (unit smaller/larger than 5) and a parity judgment task (even/odd) on two-digit numbers. In both these primary tasks, decades were irrelevant. After some of the primary task trials (randomly), participants were asked to additionally solve a secondary task based on the previously presented number. In Experiment 1, they had to decide whether the two-digit number presented for the primary task was larger or smaller than 50. Thus, for the secondary task decades were relevant. In contrast, in Experiment 2, the secondary task was a color judgment task, which means decades were irrelevant. In Experiment 1, decades' and units' magnitudes influenced the spatial association of numbers separately. In contrast, in Experiment 2, only the units were spatially associated with magnitude. It was concluded that multiple number lines (one for units and one for decades) can be activated if attention is focused on multiple, separate magnitude attributes.

Mirror-Image Equivalence and Interhemispheric Mirror-Image Reversal

Mirror-image confusions are common, especially in children and in some cases of neurological impairment. They can be a special impediment in activities such as reading and writing directional scripts, where mirror-image patterns (such as b and d) must be distinguished. Treating mirror images as equivalent, though, can also be adaptive in the natural world, which carries no systematic left-right bias and where the same object or event can appear in opposite viewpoints. Mirror-image equivalence and confusion are natural consequences of a bilaterally symmetrical brain. In the course of learning, mirror-image equivalence may be established through a process of symmetrization, achieved through homotopic interhemispheric exchange in the formation of memory circuits. Such circuits would not distinguish between mirror images. Learning to discriminate mirror-image discriminations may depend either on existing brain asymmetries, or on extensive learning overriding the symmetrization process. The balance between mirror-image equivalence and mirror-image discrimination may nevertheless be precarious, with spontaneous confusions or reversals, such as mirror writing, sometimes appearing naturally or as a manifestation of conditions like dyslexia.

Connections are not enough for membership: Letter/non-letter distinction persists through phonological association learning

In compound, hierarchical stimuli (also known as Navon figures), a Global Precedence Effect (GPE) can reliably be observed for both letters and non-letters. However, when presentation conditions sufficiently resemble those of reading, the GPE for letters has occasionally been found to disappear. We corroborate this effect in a study with a large group of participants. In addition, in-between two sessions, participants were trained in associating the non-letters with either phonological or non-phonological sounds. We reasoned that learning distinctive phonological associations might be akin to the acquisition of letter knowledge. This might eliminate the GPE also for the non-letters. However, the GPE persisted for the trained non-letters in both conditions. The large number of participants in this study revealed additional effects in the letter condition, which enabled further insights in the processing dissociation between letters and non-letter shapes.

Challenging Cognitive Control by Mirrored Stimuli in Working Memory Matching

Cognitive conflict has often been investigated by placing automatic processing originating from learned associations in competition with instructed task demands. Here we explore whether mirror generalization as a congenital mechanism can be employed to create cognitive conflict. Past research suggests that the visual system automatically generates an invariant representation of visual objects and their mirrored counterparts (i.e., mirror generalization), and especially so for lateral reversals (e.g., a cup seen from the left side vs. right side). Prior work suggests that mirror generalization can be reduced or even overcome by learning (i.e., for those visual objects for which it is not appropriate, such as letters d and b). We, therefore, minimized prior practice on resolving conflicts involving mirror generalization by using kanji stimuli as non-verbal and unfamiliar material. In a 1-back task, participants had to check a stream of kanji stimuli for identical repetitions and avoid miss-categorizing mirror reversed stimuli as exact repetitions. Consistent with previous work, lateral reversals led to profound slowing of reaction times and lower accuracy in Experiment 1. Yet, different from previous reports suggesting that lateral reversals lead to stronger conflict, similar slowing for vertical and horizontal mirror transformations was observed in Experiment 2. Taken together, the results suggest that transformations of visual stimuli can be employed to challenge cognitive control in the 1-back task.

Shared Book Reading Promotes Not Only Language Development, But Also Grapheme Awareness in German Kindergarten Children

Effects of shared book reading on expressive vocabulary and grapheme awareness without letter instruction in German kindergarteners (longitudinal; N = 69, 3;0–4;8 years) were investigated. Expressive vocabulary was measured by using a standardized test; grapheme awareness was measured by asking children to identify one grapheme per trial presented amongst non-letter distractors. Two methods of shared book reading were investigated, literacy enrichment (additional books) and teacher training in shared book reading strategies, both without explicit letter instruction. Whereas positive effects of shared book reading on expressive vocabulary were evident in numerous previous studies, the impact of shared book reading on grapheme awareness has not yet been investigated. Both methods resulted in positive effects on children’s expressive vocabulary and grapheme awareness over a period of 6 months. Thus, early shared book reading may not only be considered to be a tool for promoting the development of expressive vocabulary, but also for implicit acquisition of grapheme awareness. The latter is considered an important precondition required for the explicit learning of grapheme–phoneme conversion rules (letter knowledge).

DOES DYSLEXIA DEVELOP FROM LEFT-EYE DOMINANCE?

The purpose of this theoretical analysis and synthesis is to indicate how left-eye sighting dominance may lead to reading failure through dysfunctional right hemisphere letter encoding. Differing compensatory strategies are postulated to lead to outcomes that include the development of the phonologically impaired and phonologically proficient subtypes of dyslexia as well as specific spelling disability. Evidence is presented indicating that these disorders might be prevented by delaying the introduction of letter writing until the age of 8 years. Early childhood speech categorization in children genetically at-risk of developing dyslexia is also considered from this perspective. Convergent support for this premature writing hypothesis is provided by a comparison with the development of the left-hand inverted writing posture.

Timing the impact of literacy on visual processing

Learning to read requires the acquisition of an efficient visual procedure for quickly recognizing fine print. Thus, reading practice could induce a perceptual learning effect in early vision. Using functional magnetic resonance imaging (fMRI) in literate and illiterate adults, we previously demonstrated an impact of reading acquisition on both high- and low-level occipitotemporal visual areas, but could not resolve the time course of these effects. To clarify whether literacy affects early vs. late stages of visual processing, we measured event-related potentials to various categories of visual stimuli in healthy adults with variable levels of literacy, including completely illiterate subjects, early-schooled literate subjects, and subjects who learned to read in adulthood (ex-illiterates). The stimuli included written letter strings forming pseudowords, on which literacy is expected to have a major impact, as well as faces, houses, tools, checkerboards, and false fonts. To evaluate the precision with which these stimuli were encoded, we studied repetition effects by presenting the stimuli in pairs composed of repeated, mirrored, or unrelated pictures from the same category. The results indicate that reading ability is correlated with a broad enhancement of early visual processing, including increased repetition suppression, suggesting better exemplar discrimination, and increased mirror discrimination, as early as ∼ 100-150 ms in the left occipitotemporal region. These effects were found with letter strings and false fonts, but also were partially generalized to other visual categories. Thus, learning to read affects the magnitude, precision, and invariance of early visual processing.

Reading as functional coordination: not recycling but a novel synthesis

The Functional Coordination approach describes the processes involved in learning to read as a form of procedural learning in which pre-existing skills, mainly from the visual, and auditory domain, are (1) recruited, (2) modified, and (3) coordinated to create the procedures for reading text, which form the basis of subsequent (4) automatization. In this context, we discuss evidence relating to the emerging prevalence of analytic processing in letter perception. We argue that the process of learning to read does not have to lead to a loss of perceptual skill as consequence of a "cultural recycling"; learning to read just leads to a novel synthesis of functions, which are coordinated for reading and then automatized as a package over several years. Developmental dyslexia is explained within this framework as a Functional Coordination Deficit (Lachmann, 2002), since the coordination level is assumed to be most liable to manifest deficiencies. This is because, at this level, the greatest degree of fine tuning of complex functions is required. Thus, developmental dyslexia is not seen as a consequence of a deficient automatization per se, but of automatization of abnormally developed functional coordination.

Letters in the forest: global precedence effect disappears for letters but not for non-letters under reading-like conditions

Normally skilled reading involves special processing strategies for letters, which are habitually funneled into an abstract letter code. On the basis of previous studies we argue that this habit leads to the preferred usage of an analytic strategy for the processing of letters, while non-letters are preferably processed via a holistic strategy. The well-known global precedence effect (GPE) seems to contradict to this assumption, since, with compound, hierarchical figures, including letter items, faster responses are observed to the global than to the local level of the figure, as well as an asymmetric interference effect from global to local level. We argue that with letters these effects depend on presentation conditions; only when they elicit the processing strategies automatized for reading, an analytic strategy for letters in contrast to non-letters is to be expected. We compared the GPE for letters and non-letters in central viewing, with the global stimulus size close to the functional visual field in whole word reading (6.5° of visual angle) and local stimuli close to the critical size for fluent reading of individual letters (0.5° of visual angle). Under these conditions, the GPE remained robust for non-letters. For letters, however, it disappeared: letters showed no overall response time advantage for the global level and symmetric congruence effects (local-to-global as well as global-to-local interference). We interpret these results as according to the view that reading is based on resident analytic visual processing strategies for letters.

Neural correlates of letter reversal in children and adults

Children often make letter reversal errors when first learning to read and write, even for letters whose reversed forms do not appear in normal print. However, the brain basis of such letter reversal in children learning to read is unknown. The present study compared the neuroanatomical correlates (via functional magnetic resonance imaging) and the electrophysiological correlates (via event-related potentials or ERPs) of this phenomenon in children, ages 5-12, relative to young adults. When viewing reversed letters relative to typically oriented letters, adults exhibited widespread occipital, parietal, and temporal lobe activations, including activation in the functionally localized visual word form area (VWFA) in left occipito-temporal cortex. Adults exhibited significantly greater activation than children in all of these regions; children only exhibited such activation in a limited frontal region. Similarly, on the P1 and N170 ERP components, adults exhibited significantly greater differences between typical and reversed letters than children, who failed to exhibit significant differences between typical and reversed letters. These findings indicate that adults distinguish typical and reversed letters in the early stages of specialized brain processing of print, but that children do not recognize this distinction during the early stages of processing. Specialized brain processes responsible for early stages of letter perception that distinguish between typical and reversed letters may develop slowly and remain immature even in older children who no longer produce letter reversals in their writing.

Does viotin activate violin more than viocin? On the use of visual cues during visual-word recognition

The vast majority of neural and computational models of visual-word recognition assume that lexical access is achieved via the activation of abstract letter identities. Thus, a word's overall shape should play no role in this process. In the present lexical decision experiment, we compared word-like pseudowords like viotín (same shape as its base word: violín) vs. viocín (different shape) in mature (college-aged skilled readers), immature (normally reading children), and immature/impaired (young readers with developmental dyslexia) word-recognition systems. Results revealed similar response times (and error rates) to consistent-shape and inconsistent-shape pseudowords for both adult skilled readers and normally reading children - this is consistent with current models of visual-word recognition. In contrast, young readers with developmental dyslexia made significantly more errors to viotín-like pseudowords than to viocín-like pseudowords. Thus, unlike normally reading children, young readers with developmental dyslexia are sensitive to a word's visual cues, presumably because of poor letter representations.

E-readers are more effective than paper for some with dyslexia

E-readers are fast rivaling print as a dominant method for reading. Because they offer accessibility options that are impossible in print, they are potentially beneficial for those with impairments, such as dyslexia. Yet, little is known about how the use of these devices influences reading in those who struggle. Here, we observe reading comprehension and speed in 103 high school students with dyslexia. Reading on paper was compared with reading on a small handheld e-reader device, formatted to display few words per line. We found that use of the device significantly improved speed and comprehension, when compared with traditional presentations on paper for specific subsets of these individuals: Those who struggled most with phoneme decoding or efficient sight word reading read more rapidly using the device, and those with limited VA Spans gained in comprehension. Prior eye tracking studies demonstrated that short lines facilitate reading in dyslexia, suggesting that it is the use of short lines (and not the device per se) that leads to the observed benefits. We propose that these findings may be understood as a consequence of visual attention deficits, in some with dyslexia, that make it difficult to allocate attention to uncrowded text near fixation, as the gaze advances during reading. Short lines ameliorate this by guiding attention to the uncrowded span.

The influence of reading expertise in mirror-letter perception: Evidence from beginning and expert readers

The visual word recognition system recruits neuronal systems originally developed for object perception which are characterized by orientation insensitivity to mirror reversals. It has been proposed that during reading acquisition beginning readers have to "unlearn" this natural tolerance to mirror reversals in order to efficiently discriminate letters and words. Therefore, it is supposed that this unlearning process takes place in a gradual way and that reading expertise modulates mirror-letter discrimination. However, to date no supporting evidence for this has been obtained. We present data from an eye-movement study that investigated the degree of sensitivity to mirror-letters in a group of beginning readers and a group of expert readers. Participants had to decide which of the two strings presented on a screen corresponded to an auditorily presented word. Visual displays always included the correct target word and one distractor word. Results showed that those distractors that were the same as the target word except for the mirror lateralization of two internal letters attracted participants' attention more than distractors created by replacement of two internal letters. Interestingly, the time course of the effects was found to be different for the two groups, with beginning readers showing a greater tolerance (decreased sensitivity) to mirror-letters than expert readers. Implications of these findings are discussed within the framework of preceding evidence showing how reading expertise modulates letter identification.

The neurophysiological basis of the integration of written and heard syllables in dyslexic adults

OBJECTIVE

Letter-speech sound integration in fluent readers takes place automatically and is dependent on temporal synchrony between letters and sounds. In developmental dyslexia, however, letter-speech sound associations are hard to learn, compromising accurate and fluent reading. We studied the effect of printed text on processing speech sounds in dyslexic and fluent adult readers.

METHODS

Visual stimuli were presented with sequences of spoken syllables including vowel or consonant changes, or changes in syllable intensity, frequency, or vowel duration. As visual material, written syllables or their scrambled images were used. The auditory stimuli were presented either synchronously with the visual stimuli or time delayed. The mismatch negativity (MMN), an index of automatic neural change detection, was recorded.

RESULTS

MMN amplitudes were larger to syllable changes in combination with written syllables than with scrambled images in fluent readers. However, dyslexic readers showed no difference between syllables vs. scrambled image condition. Furthermore, MMNs to consonant and frequency changes peaked later in dyslexic than fluent readers.

CONCLUSIONS

Our results suggest deficient and sluggish audiovisual integration in dyslexic individuals, which is not dependent on the phonological relevance of the deviant type.

SIGNIFICANCE

Unlike previous studies, our study included several different types of syllable changes presented with concurrent print, enabling us to determine in more detail the nature of the audiovisual deficit in dyslexia.

Learning to read aligns visual analytical skills with grapheme-phoneme mapping: evidence from illiterates

Learning to read puts evolutionary established speech and visual object recognition functions to novel use. As we previously showed, this leads to particular rearrangements and differentiations in these functions, for instance the habitual preference for holistic perceptual organization in visual object recognition and its suppression in perceiving letters. We performed the experiment in which the differentiation between holistic non-letter processing and analytic letter processing in literates was originally shown (van Leeuwen and Lachmann, 2004) with illiterate adults. The original differentiation is absent in illiterates; they uniformly showed analytic perception for both letters and non-letters. The result implies that analytic visual perception is not a secondary development resulting from learning to read but, rather, a primary mode of perceptual organization on a par with holistic perception.

Effect of orthographic processes on letter identity and letter-position encoding in dyslexic children

The ability to identify letters and encode their position is a crucial step of the word recognition process. However and despite their word identification problem, the ability of dyslexic children to encode letter identity and letter-position within strings was not systematically investigated. This study aimed at filling this gap and further explored how letter identity and letter-position encoding is modulated by letter context in developmental dyslexia. For this purpose, a letter-string comparison task was administered to French dyslexic children and two chronological age (CA) and reading age (RA)-matched control groups. Children had to judge whether two successively and briefly presented four-letter strings were identical or different. Letter-position and letter identity were manipulated through the transposition (e.g., RTGM vs. RMGT) or substitution of two letters (e.g., TSHF vs. TGHD). Non-words, pseudo-words, and words were used as stimuli to investigate sub-lexical and lexical effects on letter encoding. Dyslexic children showed both substitution and transposition detection problems relative to CA-controls. A substitution advantage over transpositions was only found for words in dyslexic children whereas it extended to pseudo-words in RA-controls and to all type of items in CA-controls. Letters were better identified in the dyslexic group when belonging to orthographically familiar strings. Letter-position encoding was very impaired in dyslexic children who did not show any word context effect in contrast to CA-controls. Overall, the current findings point to a strong letter identity and letter-position encoding disorder in developmental dyslexia.

Eliciting dyslexic symptoms in proficient readers by simulating deficits in grapheme-to-phoneme conversion and visuo-magnocellular processing

Among the cognitive causes of dyslexia, phonological and magnocellular deficits have attracted a substantial amount of research. Their role and their exact impact on reading ability are still a matter of debate, partly also because large samples of dyslexics are hard to recruit. Here, we report a new technique to simulate dyslexic symptoms in normal readers in two ways. Although difficulties in grapheme-to-phoneme conversion were elicited by manipulating the identifiability of written letters, visual-magnocellular processing deficits were generated by presenting letters moving dynamically on the screen. Both factors were embedded into a lexical word-pseudoword decision task with proficient German readers. Although both experimental variations systematically increased lexical decision times, they did not interact. Subjects successfully performed word-pseudoword distinctions at all levels of simulation, with consistently longer reaction times for pseudowords than for words. Interestingly, detecting a pseudoword was more difficult in the grapheme-to-phoneme conversion simulation as indicated by a significant interaction of word type and letter shape. These behavioural effects are consistent with those observed in 'real' dyslexics in the literature. The paradigm is thus a potential means of generating novel hypotheses about dyslexia, which can easily be tested with normal readers before screening and recruiting real dyslexics.

The neural signature of orthographic-phonological binding in successful and failing reading development

Learning to read in alphabetic orthographies starts with learning a script code consisting of letter-speech sound pairs. Although children know which letters belong to which speech sounds within months, it takes much longer to automatically integrate them into newly constructed audiovisual objects. This extended learning process corresponds with observations that reliable letter and word specific activations in the fusiform cortex also occur relatively late in reading development. The present review discusses electrophysiological and neuroimaging studies of the nature and mechanisms involved in letter-speech sound integration in normal and dyslexic readers. It is demonstrated that letter-speech sound associations do not develop in parallel with visual letter recognition but immediately work in concert to form orthographic-phonological bonds which remain active even in experienced reading. Effective letter-speech sound integration may be necessary for reliable letter recognition to develop. In contrast, it is this basic integration of letters and speech sounds which poses an immediate problem for beginning dyslexic readers, and remains problematic in adult dyslexic readers. It is hypothesized that a specific orthographic-phonological binding deficit may not only act as a proximal cause for reading deficits in dyslexia, but may also explain the notorious lack of reading fluency. Finally, it is suggested that similar integrated audiovisual representations may also exist for larger grain-sizes in the same posterior occipitotemporal/inferoparietal network as identified for orthographic-phonological integration of letters and speech sounds.

Procedural learning and dyslexia

Three major 'neural systems', specialized for different types of information processing, are the sensory, declarative, and procedural systems. It has been proposed (Trends Neurosci., 30(4), 135-141) that dyslexia may be attributable to impaired function in the procedural system together with intact declarative function. We provide a brief overview of the increasing evidence relating to the hypothesis, noting that the framework involves two main claims: first that 'neural systems' provides a productive level of description avoiding the underspecificity of cognitive descriptions and the overspecificity of brain structural accounts; and second that a distinctive feature of procedural learning is its extended time course, covering from minutes to months. In this article, we focus on the second claim. Three studies-speeded single word reading, long-term response learning, and overnight skill consolidation-are reviewed which together provide clear evidence of difficulties in procedural learning for individuals with dyslexia, even when the tasks are outside the literacy domain. The educational implications of the results are then discussed, and in particular the potential difficulties that impaired overnight procedural consolidation would entail. It is proposed that response to intervention could be better predicted if diagnostic tests on the different forms of learning were first undertaken.

Interaction of phonological awareness and 'magnocellular' processing during normal and dyslexic reading: behavioural and fMRI investigations

We investigated whether phonological deficits are a consequence of magnocellular processing deficits in dyslexic and control children. In Experiment 1, children were tested for reading ability, phonological awareness, visuo-magnocellular motion perception, and attention shifting (sometimes considered as magnocellular function). A two-step cluster analysis of the behavioural scores revealed four clusters of children. Phonological awareness was correlated with attention (cluster musical sharp1) or motion detection (cluster musical sharp2), whereas attention and motion detection were correlated in cluster musical sharp3. In cluster musical sharp4, all variables were uncorrelated. In Experiment 2, the same variables plus auditory discrimination were tested with fMRI in a sub-sample of Experiment 1. Although dyslexics had reduced activation in visual or auditory cortex during motion detection or auditory discrimination, respectively, they had increased right frontal activation in areas 44 and 45 in all 'magnocellular' (including auditory) tasks. In contrasts, during phonological decisions, there was higher activation for good readers than dyslexics in left areas 44 and 45. Together, the two experiments give insight into the interplay of phonological and magnocellular processing during reading. Distinct left versus right frontal effects reveal partly different underlying neural mechanisms. These data contradict the view that phonological processing deficits in dyslexia necessarily result from impaired magnocellular functioning.

Representational economy, not processing speed, determines preferred processing strategy of visual patterns

According to Garner, visual patterns are mentally represented as categories rather than by their physical identity. On the other hand, physical and categorical identification tasks engender their own specific processing strategies. Nevertheless, categorical strategies should be more generic than physical ones. We tested this prediction using Garner patterns in a same-different task: one version involved categorical, the other physical identification. Both tasks showed effects of categorical representation but also contrasting categorical and physical processing strategies in their response time profiles. When trials from categorical and physical identification tasks were randomly intermixed, mixing costs were additive for categorical trials but not for physical trials, indicating a shift in processing strategy for the latter. For these trials, the physical response time profile was found to be displaced by a categorical profile. We concluded that the more generic processing strategy is the one that maximizes the role of categorical representation.

Controlled but independent: effects of mental rotation and developmental dyslexia in dual-task settings

In two experiments, we compared the performance of normal-reading (n = 26) and dyslexic children (n = 22) in discriminating letters from their mirrored images. In experiment 1, they were always presented in the upright orientation; in experiment 2, they were presented in different angular orientations (0 degrees, 90 degrees, 180 degrees). In order to determine whether task and dyslexia affect reaction times in early or late stages of processing, a dual-task paradigm was adopted in which the primary task was tone discrimination. Stimulus onset asynchrony (SOA) between first and second task was systematically varied (50 ms versus 400 ms). In both experiments dyslexics were slower overall than controls. No effects of mirror-image letters were found. In experiment 2, mental-rotation effects were additive with SOA. In accordance with earlier findings we concluded that the mental-rotation effect involves central processing capacity. Mental-rotation effects were the same for normal-reading and dyslexic children; mental rotation is not impaired in dyslexia. Remarkably, SOA effects were larger in normal readers than in dyslexics. This result was explained by observing that dyslexics experience decision difficulties already on the first task. As a result, they do not benefit optimally from increased latencies between first and second tasks.

Dissociating congruence effects in letters versus shapes: Kanji and kana

In order to consolidate the dissociation in feature integration found in earlier studies between letters of the Roman alphabet and corresponding pseudo-letters, the present study used kanji and kana and corresponding pseudo-letters, presented visually, either in isolation or surrounded by congruent or incongruent shape, as targets in a choice-response task with three different response criteria. When the criterion was shape, congruence effects were obtained for both real and pseudo-letters. With the second and third response criteria this result was found for pseudo-letters, but not for letters. These criteria either involved distinguishing between letters and visually similar pseudo-letters or distinguishing between visually similar letters. The dissociation of congruence effects between letters and pseudo-letters was therefore shown to depend on visual similarity between targets, independent of their category. This effect was found to be robust for kanji but not for kana, which is related to distinctions between these two writing systems.

Differentiation of holistic processing in the time course of letter recognition

Pairs of letters, pseudo-letters, and basic geometrical shapes were presented in a sequential same-different task, in which the time between the first and second items was varied. The second item was either presented in isolation or surrounded by an irrelevant geometrical shape that could be congruent or incongruent to the target. Congruence effects were obtained for shapes and pseudo-letters, but not for letters if the interval between the first and second items was short. Absence of congruence effects was interpreted, in accordance with earlier findings, as categorical influence on early visual integration processes; letters are processed less holistically than non-letter shapes. The present result indicates that categorical influence of letters depends on the time course of stimulus processing. As a highly automatized process, it is effective for stimuli appearing at a relatively fast rate, whereas, a slower rate of stimulus presentation eliminates task-irrelevant categorical influences.