Rate- and Accuracy-Disabled Subtype Profiles Among Adults With Dyslexia in the Hebrew Orthography

Reduced Implicit but not Explicit Knowledge of Cross-Situational Statistical Learning in Developmental Dyslexia

Although statistical learning (SL) has been studied extensively in developmental dyslexia (DD), less attention has been paid to other fundamental challenges in language acquisition, such as cross-situational word learning. Such investigation is important for determining whether and how SL processes are affected in DD at the word level. In this study, typically developed (TD) adults and young adults with DD were exposed to a set of trials that contained multiple spoken words and multiple pictures of individual objects, with no information about word-referent correspondences provided within a trial. Nonetheless, cross-trial statistical relations could be exploited to learn word-referent mappings. The degree of within-trial reference uncertainty and the novelty of to-be-learned objects (novel or familiar) were varied under different learning conditions. The results show that across all conditions, young adults with DD were significantly impaired in their ability to exploit cross-trial regularities in co-occurring visual-auditory streams to discover word-referent mappings. Observed impairments were most pronounced when within-trial reference uncertainty was the highest. Subjective measures of knowledge awareness revealed greater development of implicit but not explicit knowledge in the TD group than in the DD group. Together, these findings suggest that the SL deficit in DD affects fundamental language learning challenges at the word level and points to greater reliance on explicit processes due to impaired implicit associative learning among individuals with DD. Such a deficit is likely to influence spoken language acquisition, and in turn affect literacy skills, in people with DD.

Revisiting Multifactor Models of Dyslexia: Do They Fit Empirical Data and What Are Their Implications for Intervention?

Developmental dyslexia can be viewed as the result of the effects of single deficits or multiple deficits. This study presents a test of the applicability of a multifactor-interactive model (MFi-M) with a preliminary set of five variables corresponding to different neuropsychological functions involved in the reading process. The model has been tested on a sample of 55 school-age children with developmental dyslexia. The results show that the data fit a model in which each variable contributes to the reading ability in a non-additive but rather interactive way. These findings constitute a preliminary validation of the plausibility of the MFi-M, and encourage further research to add relevant factors and specify their relative weights. It is further discussed how subtype-based intervention approaches can be a suitable and advantageous framework for clinical intervention in a MFi-M perspective.

Atypical Reinforcement Learning in Developmental Dyslexia

OBJECTIVES

According to the Procedural Deficit Hypothesis, abnormalities in corticostriatal pathways could account for the language-related deficits observed in developmental dyslexia. The same neural network has also been implicated in the ability to learn contingencies based on trial and error (i.e., reinforcement learning [RL]). On this basis, the present study tested the assumption that dyslexic individuals would be impaired in RL compared with neurotypicals in two different tasks.

METHODS

In a probabilistic selection task, participants were required to learn reinforcement contingencies based on probabilistic feedback. In an implicit transitive inference task, participants were also required to base their decisions on reinforcement histories, but feedback was deterministic and stimulus pairs were partially overlapping, such that participants were required to learn hierarchical relations.

RESULTS

Across tasks, results revealed that although the ability to learn from positive/negative feedback did not differ between the two groups, the learning of reinforcement contingencies was poorer in the dyslexia group compared with the neurotypicals group. Furthermore, in novel test pairs where previously learned information was presented in new combinations, dyslexic individuals performed similarly to neurotypicals.

CONCLUSIONS

Taken together, these results suggest that learning of reinforcement contingencies occurs less robustly in individuals with developmental dyslexia. Inferences for the neuro-cognitive mechanisms of developmental dyslexia are discussed.

Preventing the Development of Dyslexia: A Premature Writing Hypothesis

It has been argued that dyslexia may develop in strongly left eye dominant children through learning to write using ipsilateral, right hemisphere motor pathways. New light on this theory has been cast by recent findings of atypical enhanced corpus callosum white matter in children with dyslexia, reflecting right to left hemisphere communication that is resistant to intensive remedial reading intervention. Enhanced corpus callosum white matter is consistent with uninhibited right to left hemisphere ipsilateral mirror-motor innervation, manifested as frequent mirror-letter writing errors in children with dyslexia. Delaying writing instruction until 7-8 years of age may prevent these errors and as well as the development of dyslexia. During the 7-8 year age period, visual-proprioceptive integration enables a child to mentally map whole word visual images onto kinaesthetic/proprioceptive letter engrams (memory representations). Hypothetically, this process is facilitated by anterior commissure activity involving inter-hemispheric transfer of ipsilateral mirror-to-non mirror motor movement. This postulate, involving delayed writing instruction pending further maturation, also receives indirect support from the remarkable proficiency leap among second graders reading Hebrew as Hebrew involves a leftward orthography in which ipsilateral right to left hemisphere innervation is uninhibited. Additionally, and more directly, normal reading comprehension for learning English among children with agenesis of the corpus callosum suggests that letter-sound decoding is not the sole route to proficient reading comprehension. In this paper, I make recommendations for obtaining empirical evidence of premature writing as a cause of dyslexia.

Evidence from ERP and Eye Movements as Markers of Language Dysfunction in Dyslexia

Developmental dyslexia is a complex reading disorder involving genetic and environmental factors. After more than a century of research, its etiology remains debated. Two hypotheses are often put forward by scholars to account for the causes of dyslexia. The most common one, the linguistic hypothesis, postulates that dyslexia is due to poor phonological awareness. The alternative hypothesis considers that dyslexia is caused by visual-attentional deficits and abnormal eye movement patterns. This article reviews a series of selected event-related brain potential (ERP) and eye movement studies on the reading ability of dyslexic individuals to provide an informed state of knowledge on the etiology of dyslexia. Our purpose is to show that the two abovementioned hypotheses are not necessarily mutually exclusive, and that dyslexia should rather be considered as a multifactorial deficit.

Increased reliance on top-down information to compensate for reduced bottom-up use of acoustic cues in dyslexia

Speech recognition is a complex human behavior in the course of which listeners must integrate the detailed phonetic information present in the acoustic signal with their general linguistic knowledge. It is commonly assumed that this process occurs effortlessly for most people, but it is still unclear whether this also holds true in the case of developmental dyslexia (DD), a condition characterized by perceptual deficits. In the present study, we used a dual-task setting to test the assumption that speech recognition is effortful for people with DD. In particular, we tested the Ganong effect (i.e., lexical bias on phoneme identification) while participants performed a secondary task of either low or high cognitive demand. We presumed that reduced efficiency in perceptual processing in DD would manifest in greater modulation in the performance of primary task by cognitive load. Results revealed that this was indeed the case. We found a larger Ganong effect in the DD group under high than under low cognitive load, and this modulation was larger than it was for typically developed (TD) readers. Furthermore, phoneme categorization was less precise in the DD group than in the TD group. These findings suggest that individuals with DD show increased reliance on top-down lexically mediated perception processes, possibly as a compensatory mechanism for reduced efficiency in bottom-up use of acoustic cues. This indicates an imbalance between bottom-up and top-down processes in speech recognition of individuals with DD.

Delaying feedback compensates for impaired reinforcement learning in developmental dyslexia

A theoretical framework suggests that developmental dyslexia is characterized by abnormalities in brain structures underlying the procedural learning and memory systems while the declarative learning and memory systems are presumed to remain intact or even enhanced (Procedural Deficit Hypothesis). This notion has been supported by a substantial body of research, which focused on each system independently. However, less attention has been paid to interactions between these memory systems which may provide insights as to learning situations and conditions in which learning in dyslexia can be improved. The current study was undertaken to examine these important but unresolved issues. To this end, probabilistic reinforcement learning and episodic memory tasks were examined in participants with dyslexia and neurotypicals simultaneously within a single task. Feedback timing presentation was manipulated, building on prior research indicating that delaying feedback timing shifts striatal-based probabilistic learning, to become more hippocampal-dependent. It was hypothesized that if the procedural learning and memory systems are impaired in dyslexia, performance will be impaired under conditions that encourage procedural memory engagement (immediate feedback trials) but not under conditions that promote declarative memory processing (long delayed feedback trials). It was also predicted that the ability to incidentally acquire episodic information would be preserved in dyslexia. The results supported these predictions. Participants with dyslexia were impaired in probabilistic learning of cue-outcome associations compared to neurotypicals in an immediate feedback condition, but not when feedback on choices was presented after a long delay. Furthermore, participants with dyslexia demonstrated similar performance to neurotypicals in a task requiring incidental episodic memory formation. These findings attest to a dissociation between procedural-based and declarative-based learning in developmental dyslexia within a single task, a finding that adds discriminative validity to the Procedural Deficit Hypothesis. Just as important, the present findings suggest that training conditions designed to shift the load from midbrain/striatal systems to declarative memory mechanisms have the potential to compensate for impaired learning in developmental dyslexia.

Functional Connectivity in Developmental Dyslexia during Speed Discrimination

A universal signature of developmental dyslexia is literacy acquisition impairments. Besides, dyslexia may be related to deficits in selective spatial attention, in the sensitivity to global visual motion, speed processing, oculomotor coordination, and integration of auditory and visual information. Whether motion-sensitive brain areas of children with dyslexia can recognize different speeds of expanded optic flow and segregate the slow-speed from high-speed contrast of motion was a main question of the study. A combined event-related EEG experiment with optic flow visual stimulation and functional frequency-based graph approach (small-world propensity ϕ) were applied to research the responsiveness of areas, which are sensitive to motion, and also distinguish slow/fast -motion conditions on three groups of children: controls, untrained (pre-D) and trained dyslexics (post-D) with visual intervention programs. Lower ϕ at θ, α, γ1-frequencies (low-speed contrast) for controls than other groups represent that the networks rewire, expressed at β frequencies (both speed contrasts) in the post-D, whose network was most segregated. Functional connectivity nodes have not existed in pre-D at dorsal medial temporal area MT+/V5 (middle, superior temporal gyri), left-hemispheric middle occipital gyrus/visual V2, ventral occipitotemporal (fusiform gyrus/visual V4), ventral intraparietal (supramarginal, angular gyri), derived from θ-frequency network for both conditions. After visual training, compensatory mechanisms appeared to implicate/regain these brain areas in the left hemisphere through plasticity across extended brain networks. Specifically, for high-speed contrast, the nodes were observed in pre-D (θ-frequency) and post-D (β2-frequency) relative to controls in hyperactivity of the right dorsolateral prefrontal cortex, which might account for the attentional network and oculomotor control impairments in developmental dyslexia.

Is orthographic knowledge a strength or a weakness in individuals with dyslexia? Evidence from a meta-analysis

The purpose of this meta-analysis was to examine if individuals with dyslexia (DYS) have a deficit in orthographic knowledge. We reviewed a total of 68 studies published between January 1990 and December 2019, representing a total of 7215 participants. There were 80 independent samples in the chronological-age (CA)-DYS comparison and 33 independent samples in the comparison between DYS and reading-level (RL) controls. A random-effects model analysis revealed a large effect size (Cohen's d = 1.17) for the CA-DYS comparison and a small effect size (Cohen's d = 0.18) for the RL-DYS comparison. In addition, we found significant heterogeneity in the effect sizes that was partly explained by the level of orthographic knowledge (effect sizes being higher for lexical than sub-lexical orthographic knowledge). These results suggest that individuals with dyslexia experience an orthographic knowledge deficit that is as large as that of phonological awareness and rapid automatized naming reported in previous meta-analyses.

Global and Local Visual Processing in Rate/Accuracy Subtypes of Dyslexia

Words are processed in both a global and local manner. Studies on global versus local processing styles in individuals with and without dyslexia are inconclusive. In the present study, we investigated whether distinct patterns of global/local visual processing were associated with more precisely defined dyslexia profiles. Previous studies on dyslexia provide evidence of accuracy- and rate-based subtypes, with impairment in one dimension alongside normal performance in the other. In the current study, three groups of adult readers: rate disability, accuracy disability, typical development, were presented with nonlinguistic global /local congruency task. The results revealed that the rate disability group had deficiencies performing the global task while the accuracy disability group had deficiencies in the local task. These results are discussed in the context of global/local word processing and in relation to dyslexia. Specifically, they suggest that different patterns of global/local processing are observed between different types of dyslexics, and imply that practitioners should modify their treatment based on the specific deficiency.

Another Temporal Processing Deficit in Individuals With Developmental Dyslexia: The Case of Normalization for Speaking Rate

Purpose Developmental dyslexia (DD) has mostly been attributed to arise from phonological impairments; however, several theories indicate a temporal processing deficit as the underlying cause of DD. So far, research examined the influence of temporal cues on concurrent speech sound categorization in DD, but effects of temporal information from a context (e.g., speaking rate) on the perception of subsequent sounds (i.e., "rate normalization") have not been considered. This study examined whether individuals with DD are capable of implicitly extracting temporal information embedded in context and use it for phoneme categorization to the same extent as healthy readers. Method Fifteen individuals diagnosed with DD and 16 healthy readers, all native speakers of Hebrew, listened to context sentences followed by target words. They had to indicate whether the target word sounded more like taam ("taste"; a long-vowel response) or tam ("naïve"; a short-vowel response). Temporal information of the context was manipulated (slow vs. fast speaking rate sentences) as well as the vowel duration of the target in a 5-step continuum. Results Listeners with DD did use the rate context to inform their decisions but to a significantly lesser extent than healthy listeners. In addition, their categorization of the vowel duration continuum was somewhat less distinct than that of the control group. Conclusions Individuals with DD are impaired not only in tasks involving direct temporal processing, as shown in previous studies but also in the use of temporal information of a context that impacts the perception of subsequent target words. This inability to fully utilize rate normalization processes may influence the formation of abstract phonological representations in individuals with DD.

The effects of orthographic transparency and familiarity on reading Hebrew words in adults with and without dyslexia

The current study examined the effects of transparency and familiarity on word recognition in adult Hebrew dyslexic readers with a phonological processing deficit as compared to typical readers. We measured oral reading response time and accuracy of single nouns in several conditions: diacritics that provide transparent but less familiar information and vowel letters that increase orthographic transparency without compromise familiarity. In line with former studies with adult dyslexics, Hebrew-speaking adults with dyslexia were significantly slower than controls. However, both dyslexic and typical readers read unpointed words faster when vowel letters were present, indicating that they may benefit from increase in orthographic transparency, when the graphemic representations are familiar. Only dyslexics read pointed words slower than unpointed words and were more sensitive to word frequency. In unpointed words, only typical readers benefitted from the reduced competition of orthographic neighbors of longer words. Results indicate that both orthographic transparency and familiarity play an important role in word recognition. Dyslexics are impaired in decoding of smaller units and are more sensitive to reduction in the familiarity of words.

Reading difficulties in Spanish adults with dyslexia

Recent studies show that dyslexia persists into adulthood, even in highly educated and well-read people. The main characteristic that adults with dyslexia present is a low speed when reading. In Spanish, a shallow orthographic system, no studies about adults with dyslexia are available; and it is possible that the consistency of the orthographic system favours the reading fluency. The aim of this study was to get an insight of the reading characteristics of Spanish adults with dyslexia and also to infer the reading strategies that they are using. For that purpose, a group of 30 dyslexics (M age = 32 years old) and an age-matched group of 30 adults without reading disabilities completed several phonological and reading tasks: phonological awareness tasks, rapid automatic naming, lexical decision, word and pseudoword reading, letter detection and text reading. The results showed that highly educated Spanish dyslexics performed significantly worse than the control group in the majority of the tasks. Specifically, they showed difficulties reading long pseudowords, indicating problems in automating the grapheme-phoneme rules, but they also seem to present difficulties reading words, which indicate problems with the lexical route. It seems that the Spanish dyslexic adults, as in deep orthographies, continue having difficulties in phonological awareness tasks, rapid naming and reading.

A review of the neurobiological basis of dyslexia in the adult population

INTRODUCTION

Adult dyslexia affects about 4% of the population. However, studies on the neurobiological basis of dyslexia in adulthood are scarce compared to paediatric studies.

AIM

This review investigates the neurobiological basis of dyslexia in adulthood.

DEVELOPMENT

Using PsycINFO, a database of psychology abstracts, we identified 11 studies on genetics, 9 neurostructural studies, 13 neurofunctional studies and 24 neurophysiological studies. Results from the review show that dyslexia is highly heritable and displays polygenic transmission. Likewise, adult neuroimaging studies found structural, functional, and physiological changes in the parieto-occipital and occipito-temporal regions, and in the inferior frontal gyrus, in adults with dyslexia.

CONCLUSION

According to different studies, aetiology in cases of adult dyslexia is complex. We stress the need for neurobiological studies of dyslexia in languages with transparent spelling systems.

Orthographic recognition in late adolescents: an assessment through event-related brain potentials

Reading speed and efficiency are achieved through the automatic recognition of written words. Difficulties in learning and recognizing the orthography of words can arise despite reiterative exposure to texts. This study aimed to investigate, in native Spanish-speaking late adolescents, how different levels of orthographic knowledge might result in behavioral and event-related brain potential differences during the recognition of orthographic errors. Forty-five healthy high school students were selected and divided into 3 equal groups (High, Medium, Low) according to their performance on a 5-test battery of orthographic knowledge. All participants performed an orthographic recognition task consisting of the sequential presentation of a picture (object, fruit, or animal) followed by a correctly, or incorrectly, written word (orthographic mismatch) that named the picture just shown. Electroencephalogram (EEG) recording took place simultaneously. Behavioral results showed that the Low group had a significantly lower number of correct responses and increased reaction times while processing orthographical errors. Tests showed significant positive correlations between higher performance on the experimental task and faster and more accurate reading. The P150 and P450 components showed higher voltages in the High group when processing orthographic errors, whereas N170 seemed less lateralized to the left hemisphere in the lower orthographic performers. Also, trials with orthographic errors elicited a frontal P450 component that was only evident in the High group. The present results show that higher levels of orthographic knowledge correlate with high reading performance, likely because of faster and more accurate perceptual processing, better visual orthographic representations, and top-down supervision, as the event-related brain potential findings seem to suggest.

Auditory frequency discrimination in adults with dyslexia: a test of the anchoring hypothesis

PURPOSE

A recent hypothesis ascribes dyslexia to a perceptual anchoring deficit. Supporting results have so far been obtained only in children with dyslexia and additional learning difficulties, but the hypothesis has been argued to apply to all individuals with dyslexia.

METHOD

The authors measured auditory frequency discrimination thresholds in 54 young adults (native speakers of Dutch; 25 individuals with dyslexia; 29 age- and education-matched controls), with a 2-alternative forced-choice staircase paradigm. There were 2 conditions: 1 in which 1 tone in each pair had a fixed frequency across trials (standard), and 1 in which both tones varied in frequency (no standard). Presence of a standard stimulus allows the creation of a stimulus-specific representation in short-term-memory (perceptual anchor).

RESULTS

The standard condition yielded significantly lower discrimination thresholds in both controls and individuals with dyslexia; both groups benefited equally from the presence of an invariant stimulus.

CONCLUSION

There is no difference between this group of adults with dyslexia and controls in their capacity to form a perceptual anchor. The implication is that an anchoring deficit cannot be generalized to all cases of dyslexia.