Visual Motion and Decision-Making in Dyslexia: Reduced Accumulation of Sensory Evidence and Related Neural Dynamics

Abstract

Children with and without dyslexia differ in their behavioural responses to visual information, particularly when required to pool dynamic signals over space and time. Importantly, multiple processes contribute to behavioural responses. Here we investigated which processing stages are affected in children with dyslexia when performing visual motion processing tasks, by combining two methods that are sensitive to the dynamic processes leading to responses. We used a diffusion model which decomposes response time and accuracy into distinct cognitive constructs, and high-density EEG. 50 children with dyslexia (24 male) and 50 typically developing children (28 male) aged 6 to 14 years judged the direction of motion as quickly and accurately as possible in two global motion tasks (motion coherence and direction integration), which varied in their requirements for noise exclusion. Following our pre-registered analyses, we fitted hierarchical Bayesian diffusion models to the data, blinded to group membership. Unblinding revealed reduced evidence accumulation in children with dyslexia compared to typical children for both tasks. Additionally, we identified a responselocked EEG component which was maximal over centro-parietal electrodes which indicated a neural correlate of reduced drift-rate in dyslexia in the motion coherence task, thereby linking brain and behaviour. We suggest that children with dyslexia tend to be slower to extract sensory evidence from global motion displays, regardless of whether noise exclusion is required, thus furthering our understanding of atypical perceptual decision-making processes in dyslexia. Significance statementReduced sensitivity to visual information has been reported in dyslexia, with a lively debate about whether these differences causally contribute to reading difficulties. In this large preregistered study with a blind modelling approach, we combine state-of-the art methods in both computational modelling and EEG analysis to pinpoint the stages of processing that are atypical in children with dyslexia in two visual motion tasks that vary in their requirement for noise exclusion. We find reduced evidence accumulation in children with dyslexia across both tasks, and identify a neural marker, allowing us to link brain and behaviour. We show that children with dyslexia exhibit general difficulties with extracting sensory evidence from global motion displays, not just in tasks that require noise exclusion.

Integration of visual motion and orientation signals in dyslexic children: an equivalent noise approach

“…[ 36 , 41 ]) and previous studies of motion processing in dyslexia (e.g. [ 8 ]) have also relied purely on accuracy indices, group differences between dyslexic children and typically developing children have recently been shown in drift-diffusion model studies, which model both accuracy and response time data [ 52 , 69 ]. These studies have shown that dyslexic children accumulate evidence from motion displays more slowly than typically developing children.…”

“…The pattern of differences found here for dyslexic children compared to typically developing children (increased internal noise in the motion task and elevated orientation-coherence thresholds) is therefore different to that reported for autistic children. Therefore, we suggest that perceptual differences are specific to each condition (see also [ 52 , 71 ]. Accounts which suggest general impairments in motion processing across neurodevelopmental disorders (e.g.…”

“…The WASI-II, the TOWRE-2 (sight word reading efficiency and phonological decoding efficiency subtests), the WIAT-III spelling subtest and an acuity test were completed in further sessions. If children had completed the WASI-II or WIAT-III in the last 3 years as part of a previous study [ 52 , 53 ], we did not rerun these tests in order to avoid practice effects and ‘over-testing’ children. Rather we used the previously collected scores.…”

Two sides of the same coin: accessibility practices and neurodivergent users' experience of extended reality

“…Speech recognition is an effortful task for people with dyslexia, thus integrating an acoustic signal with language while performing another task can be extremely challeniging (Derawi et al, 2022). Individuals with dyslexia also have a reduced sensitivity to visual information over space and time (Manning et al, 2022).…”

Probabilistic Decision-Making in Children With Dyslexia

“…Such differences in decision-making may influence an individual’s ability to learn from phonological information for a variety of reasons, e.g., limiting the individual’s ability to properly build expected outcomes, accumulate enough information for a decision, determine probabilistic contingencies, rank competing choices, place value on the outcome after a decision, etc. Indeed, two recent studies found inefficient evidence accumulation in dyslexia ( Stefanac et al, 2021 ; Manning et al, 2022 ); however, to our knowledge, other components of decision-making in dyslexia have yet to be explored.…”