Visual motion and rapid auditory processing are solid endophenotypes of developmental dyslexia.

Motion processing after sight restoration: No competition between visual recovery and auditory compensation

Altered effective connectivity on rapid automatized naming deficits in Chinese children with developmental dyslexia: An rs-fMRI study with Ganger causality analysis

Reading is a fundamental human capacity that recruits and tunes brain circuitry subserving several neurocognitive skills. Individual differences in reading-related skills are largely influenced by genetic variation. However, the molecular basis of the heritability of reading-related skills remains narrowly replicated. Genome-wide association studies have enabled the computation of cumulative indices (polygenic scores-PGSs) aiming to capture individuals’ genetic susceptibility for a given trait. By using a multiple-mediator framework, we investigated whether the associations between a reading-specific PGS (Reading-PGS) and reading decoding and comprehension could be explained by reading-related endophenotypes (i.e., phonological awareness-PA, phonological memory, rapid auditory processing, rapid bimodal temporal processing-RBTP, and rapid automatized naming) in a sample of 8-year-old French-speaking Canadian twins (N = 328 subjects (87 MZ and 241 DZ) from 208 twin pairs—one child per MZ pairs; males, N = 159). The association between Reading-PGS and reading performance is partially mediated by PA and RBTP. Furthermore, we supported the specificity of the direct and indirect effects between Reading-PGS and reading skills after controlling for the shared genetic variation with educational attainment and cognitive ability. Finally, we uncovered a sequence from Reading-PGS to behavior mediated through sensory processing and phonological skills, supporting one of the most robust theoretical hypothesis underlying reading acquisitions. PGSs specifically targeting reading skills are essential for improved prediction and understanding of the complex etiology through which reading skills unfold during childhood. This will facilitate the early identification of children with a genetic susceptibility for reading (dis)ability at a time when these phenotypes remain malleable to intervention.

Categorization is an essential cognitive and perceptual process for decision-making and recognition. The posterior parietal cortex, particularly the lateral intraparietal (LIP) area has been suggested to transform visual feature encoding into abstract categorical representations. By contrast, areas closer to sensory input, such as the middle temporal (MT) area, encode stimulus features but not more abstract categorical information during categorization tasks. Here, we compare the contributions of the medial superior temporal (MST) and LIP areas in category computation by recording neuronal activity in both areas from two male rhesus macaques trained to perform a visual motion categorization task. MST is a core motion-processing region interconnected with MT and is often considered an intermediate processing stage between MT and LIP. We show that MST exhibits robust decision-correlated motion category encoding and working memory encoding similar to LIP, suggesting that MST plays a substantial role in cognitive computation, extending beyond its widely recognized role in visual motion processing.SIGNIFICANCE STATEMENT Categorization requires assigning incoming sensory stimuli into behaviorally relevant groups. Previous work found that parietal area LIP shows a strong encoding of the learned category membership of visual motion stimuli, while visual area MT shows strong direction tuning but not category tuning during a motion direction categorization task. Here we show that the medial superior temporal (MST) area, a visual motion-processing region interconnected with both LIP and MT, shows strong visual category encoding similar to that observed in LIP. This suggests that MST plays a greater role in abstract cognitive functions, extending beyond its well known role in visual motion processing.

A different finding on the role of cerebro-cerebellar RSFC in reading skills among Chinese children with developmental dyslexia.

The aim of the study was to examine the role of phonological processing in people with and without dyslexia, who should have already mastered the skill of reading. We tested 98 high school students aged 16–18 years, including 49 with dyslexia and 49 without. The results indicate that the participants with dyslexia, as compared with participants without dyslexia, read single words and pseudowords less correctly and slower, which is consistent with literature on the subject. In addition, they scored significantly poorer in the phoneme blending, rapid automatic naming, and backward digit span task. In the criterion group, the relationship between phonological awareness and reading fluency was much stronger, and between rapid automatic naming and reading fluency slightly weaker than in the control group. This indicates a greater influence of long-term memory on reading in high school students without dyslexia.

Excessive crowding in the visual periphery has been demonstrated in children with developmental dyslexia (DD). However, less is known about crowding in the fovea, even though foveal crowding is at least equally important, as reading is mostly accomplished through foveal vision. Here we used a special set of digitstimuli (Pelli fonts) to measure foveal crowding in DD and DD + ADHD children, and compared it to that in TD (typically developing) and ADHD children. We also used the Chinese reading acuity charts (C-READ) to assess the maximum reading speed and reading acuity, along with tests to evaluate cognitive attributes including phonological awareness, rapid automatized naming, morphological awareness, and orthographic knowledge. The results indicate significantly stronger foveal crowding in the DD and DD + ADHD groups, as well as in the ADHD group, than in the TD group. Furthermore, the DD and DD + ADHD groups exhibited poorer maximum reading speed and reading acuity compared to the ADHD and TD groups.Within the two DD groups, theslower maximum reading speed and higher reading acuitycan be predicted bystronger foveal crowding. In addition, the DD and DD + ADHD groups performed the worst in four cognitive skills, with the DD group showing negative correlations between foveal crowding and performances across all these skills. Our findings thus move beyond previously well-documented peripheral crowding in dyslexia, and the easy administration of the Pelli-font-based crowding test may be useful for early diagnosis of developmental dyslexia in young children.

We sought to better understand the neural representation of visual motion acceleration. A straightforward estimation of acceleration would involve calculating the rate of change of velocity, which itself would be calculated from change in position over time. As it is well-established that neurons in area MT encode velocity, the brain could thus indirectly estimate acceleration by calculating the change in MT’s velocity representations. An alternate mechanism, however, could operate more rapidly and directly. In this case, the brain could exploit interactions between MT’s standard motion encoding and idiosyncratic temporal dynamics of neural responses. Such direct decoding would thus exploit nonlinearities usually ignored in studies of MT coding. We tested between these two theories by measuring from ensembles of MT neurons while two male awake fixating macaques viewed linearly accelerating motion stimuli. Direct decoding of acceleration from MT was possible on faster time scales, and could be done with higher fidelity, than indirect decoding. Distinct motion acceleration information could thus be efficiently read out from rich and heterogeneous MT ensemble responses, regardless of the mechanisms that give rise to various forms of motion tuning that it exhibits. A similar analysis of activity in the medial superior temporal area (MST) did not suggest this later stage of motion processing has a more refined acceleration representation. Together, these results suggest that the brain may opportunistically exploit nonlinear idiosyncrasies of neural responses to efficiently extract behaviorally relevant information on fast time scales, instead of performing explicit calculation of some variables.

This study aims to compare the word decoding skills, phonological awareness (PA), rapid automatized naming (RAN) skills, and letter knowledge of first graders with developmental dyslexia (DD) and those who were typically developing (TD). Eighteen children with DD and eighteen TD children, matched by nonverbal intelligence and discourse ability, participated in the study. Word decoding of Korean language-based reading assessment(<xref ref-type="bibr" rid="B27">Pae <italic>et al.,</italic> 2015</xref>) was conducted. Phoneme-grapheme correspondent words were analyzed according to whether the word has meaning, whether the syllable has a final consonant, and the position of the grapheme in the syllable. Letter knowledge asked about the names and sounds of 12 consonants and 6 vowels. The children’s PA of word, syllable, body-coda, and phoneme blending was tested. Object and letter RAN was measured in seconds. The decoding difficulty of non-words was more noticeable in the DD group than in the TD one. The TD children read the syllable initial and syllable final position with 99% correctness. Children with DD read with 80% and 82% correctness, respectively. In addition, the DD group had more difficulty in decoding words with two patchims when compared with the TD one. The DD group read only 57% of words with two patchims correctly, while the TD one read 91% correctly. There were significant differences in body-coda PA, phoneme level PA, letter RAN, object RAN, and letter-sound knowledge between the two groups. This study confirms the existence of Korean developmental dyslexics, and the urgent need for the inclusion of a Korean-specific phonics approach in the education system.

The goal of the study was to investigate the overlap between developmental language disorder (DLD) and developmental dyslexia, identified through spelling difficulties (SD), in Russian-speaking children. In particular, we studied the role of phoneme awareness (PA), rapid automatized naming (RAN), pseudoword repetition (PWR), morphological (MA), and orthographic awareness (OA) in differentiating between children with DLD who have SD from children with DLD who are average spellers by comparing the two groups to each other, to typically developing children as well as children with SD but without spoken language deficits. One hundred forty-nine children, aged 10.40 to 14.00years, participated in the study. The results indicated that the SD, DLD, and DLD/SD groups did not differ from each other on PA and RAN Letters and underperformed in comparison to the control groups. However, whereas the children with written language deficits (SD and DLD/SD groups) underperformed on RAN Objects and Digits, PWR, OA, and MA, the children with DLD and no SD performed similarly to the children from the control groups on these measures. In contrast, the two groups with spoken language deficits (DLD and DLD/SD) underperformed on RAN Colors in comparison to the control groups and the group of children with SD only. The results support the notion that those children with DLD who have unimpaired PWR and RAN skills are able to overcome their weaknesses in spoken language and PA and acquire basic literacy on a par with their age peers with typical language. We also argue that our findings support a multifactorial model of DLD.

This chapter concerns the visual motion processing and detection taking place in the visual cortex of the primate brain, including the cortical areas such as the primary visual cortex (V1), the middle temporal (MT) area, and the medial superior temporal (MST) area. Specifically, the following topics are discussed: (a) the selectivity for local motion direction of the V1 neurons and the component MT neurons, (b) the aperture problem and the selectivity for global motion velocity of the pattern MT neurons, and (c) the selectivity for global optic flow patterns of the MST neurons. For each topic, the basic psychophysical and neurophysiological findings of the relevant visual cortical area will be first summarized, and then the computational models of the visual processing in the corresponding area will be presented. The computational models are hoped to serve two purposes: to help neuroscientists reveal the possible neural mechanisms for visual motion processing and perception in the brain, and to familiarize the computer scientists/engineers with the current progress in understanding the biological visual motion processing to provide additional foundation based on which new algorithms may be developed for solving computer vision problems such as motion detection and estimation.

Deficient rapid auditory processing (RAP) has been associated with early language impairment and dyslexia. Using an auditory masking paradigm, children with language disabilities perform selectively worse than controls at detecting a tone in a backward masking (BM) condition (tone followed by white noise) compared to a forward masking (FM) condition (tone preceded by white noise). Tallal's (1980) auditory processing hypothesis posits that abnormal RAP leads to reduced (or impaired) phonological awareness (PA), resulting in reading and language difficulties. Alternative theories suggest that impaired PA may have more of a top-down effect on auditory processing. The current study examines RAP in children tested at two time points, average age 5.6 and average age 8.3, in order to test causal relations between RAP and PA in a path analysis. Additional hierarchical regressions examine how well RAP predicts reading ability when accounting for PA and vocabulary. The path analysis indicates a top-down effect, such that PA has a larger impact on BM over time than the reverse. Regressions indicate no direct impact of RAP on reading ability. The path analysis provides evidence against the auditory processing hypothesis and instead suggests that between the ages of 5 and 8 it is variability in early phonological representations that predicts subsequent lower-level rapid auditory processing.

IntroductionMultisensory signals often interact to reduce perceptual uncertainty in the environment. However, the effects and mechanisms underlying audiovisual interactions in motion perception remain unclear. In this study, we adopted the method of constant stimuli and the equivalent noise paradigm to investigate whether and how auditory motion influences the perception of visual global motion.MethodsThe visual stimuli consisted of dots moving either up-left or up-right, with motion directions sampled from a normal distribution at five levels of standard deviation. The auditory stimuli were white noise moving either laterally (leftward or rightward; Experiment 1) or diagonally (up-left or up-right; Experiment 2), forming a coarse congruent or incongruent directional relationship with the visual motion trajectories. Stationary and no-sound conditions were also included. The auditory signals were task-irrelevant and presented in spatial proximity to, but not fully overlapping with, the visual stimuli. Participants had to discriminate the direction of the visual global motion.Results and discussionAfter accounting for or eliminating the bias induced by auditory motion at the decisional level, the thresholds of visual motion perception were found to be similar across the four auditory conditions. Further analysis using the equivalent noise model confirmed that auditory motion did not influence the detection or pooling of visual motion signals. Hence, we did not find evidence to support the notion that auditory motion modulates the sensory or perceptual processing of visual global motion, delineating a boundary condition for such crossmodal interactions.

Processing of visual gravitational motion in the peri-sylvian cortex: Evidence from brain-damaged patients

The three projects documented in this thesis investigated the role of three forms of attention in visual processing. Spatial, feature-based and temporal attention. The spatial and feature-based attentional characteristics were studied by conducting extracellular recordings from neurons of area MT and MSTd of macaque visual cortex. While the role of temporal attention was studied in a human psychophysics project. In the physiology projects we first defined the tuning characteristics of neurons from area MT and MSTd for two stimulus dimensions, namely spiral motion stimuli (SMS) and linear motion stimuli (LMS) on the basis of directionality index, the relative frequency of tuned versus untuned neurons, and the individual cells responses to the two forms of stimuli. We found that MT and MSTd showed differential tuning to LMS and SMS. Area MSTd demonstrated better selectivity for SMS as compared to LMS. Conversely, area MT was better tuned to LMS than SMS. Further, we compared spatial and feature-based attentional modulation in area MT and MSTd across SMS and LMS. We found that spatial attention modulates the responses of neurons in both the areas irrespective of the feature dimension defining the attended stimuli. On the other hand feature-based attention was restricted to the stimulus dimension for which an area showed better selectivity, that is SMS for MSTd and LMS for MT. We also observed that the correlation of firing rates with reaction times was restricted to an area’s preferred stimulus dimension. The presence of a significant negative correlation of firing rate with reaction time in area MSTd when attention was directed to its preferred dimension (SMS), indicated that these neurons were involved in perceptual processing of SMS. Similarly, the presence of a significant negative correlation of firing rates with the reaction times in area MT when attention was directed to LMS, provides evidence that MT neurons were involved in perceptual processing of LMS. Taken together, these results show that neurons across the visual cortex are tuned to a range of stimulus dimensions. This multiple stimulus selectivity is thought to be utilized to develop a saliency map (by interaction of bottom-up and top-down processes), which marks the behaviorally relevant aspects of visual space. These behaviorally relevant aspects of the visual space are then preferentially processed throughout the visual hierarchy, and our results suggests that a given area contributes to visual perception by flexibly processing only the stimulus dimension for which it shows best selectivity as a function of stimulus relevance. Finally in human subjects we investigated the temporal characteristics of visual motion processing, using the ‘attentional blink’ paradigm. Attentional blink is a widely studied phenomenon, but almost all studies to the date have been are restricted to stationary stimuli. We here extended this paradigm to motion stimuli. We found the presence of an attentional blink in the motion domain, in that the detection of second of the two target (motion) stimuli was severely degraded when it was presented within 450ms of the first target (motion) stimulus. However, our results were slightly different from the experiments with the stationary stimuli. First, there was an absence of the lag-1 sparing effect typically found with stationary stimuli and second, the time interval over which the attentional blink was observed was about 100ms shorter than typically reported for stationary stimuli. Post-hoc analysis showed that these effects in the motion domain were dependent upon the direction of motion of the first target. Our data showed that when the first target moved in the opposite direction to the second target, there was no attentional blink, but when the first target moved in an orthogonal direction to the second target, there was an attentional blink. These results are in agreement to previous studies showing that the processing of motion stimuli is facilitated when it is preceded by a stimulus moving in opposite directions, while processing of motion stimuli is suppressed when it is preceded by a stimulus moving in an orthogonal direction. Taken together the results of this thesis provides an important contribution to our understanding of the role of attention in visual motion processing. It will be interesting to extend this study in other visual cortical areas and measure spatial and feature-based attention from same set of neurons across different stimulus dimension.