Excessive visual crowding effects in developmental dyscalculia.

Visual crowding refers to the inability to identify objects when surrounded by other similar items. Crowding-like mechanisms are thought to play a key role in numerical perception by determining the sensory mechanisms through which ensembles are perceived. Enhanced visual crowding might hence prevent the normal development of a system involved in segregating and perceiving discrete numbers of items and ultimately the acquisition of more abstract numerical skills. Here, we investigated whether excessive crowding occurs in developmental dyscalculia (DD), a neurodevelopmental disorder characterized by difficulty in learning the most basic numerical and arithmetical concepts, and whether it is found independently of associated major reading and attentional difficulties. We measured spatial crowding in two groups of adult individuals with DD and control subjects. In separate experiments, participants were asked to discriminate the orientation of a Gabor patch either in isolation or under spatial crowding. Orientation discrimination thresholds were comparable across groups when stimuli were shown in isolation, yet they were much higher for the DD group with respect to the control group when the target was crowded by closely neighbouring flanking gratings. The difficulty in discriminating orientation (as reflected by the combination of accuracy and reaction times) in the DD compared to the control group persisted over several larger target flanker distances. Finally, we found that the degree of such spatial crowding correlated with impairments in mathematical abilities even when controlling for visual attention and reading skills. These results suggest that excessive crowding effects might be a characteristic of DD, independent of other associated neurodevelopmental disorders.

Reduced 2D form coherence and 3D structure from motion sensitivity in developmental dyscalculia.

Developmental dyscalculia (DD) is a specific learning disability affecting the development of numerical and arithmetical skills. The origin of DD is typically attributed to the suboptimal functioning of key regions within the dorsal visual stream (parietal cortex) which support numerical cognition. While DD individuals are often impaired in visual numerosity perception, the extent to which they also show a wider range of visual dysfunctions is poorly documented. In the current study we measured sensitivity to global motion (translational and flow), 2D static form (Glass patterns) and 3D structure from motion in adults with DD and control subjects. While sensitivity to global motion was comparable across groups, thresholds for static form and structure from motion were higher in the DD compared to the control group, irrespective of associated reading impairments. Glass pattern sensitivity predicted numerical abilities, and this relation could not be explained by recently reported differences in visual crowding. Since global form sensitivity has often been considered an index of ventral stream function, our findings could indicate a cortical dysfunction extending beyond the dorsal visual stream. Alternatively, they would fit with a role of parietal cortex in form perception under challenging conditions requiring multiple element integration.

External Validation of BMT-i Computerized Test Battery for Diagnosis of Learning Disabilities.

Background: Learning disabilities (LDs) are a major public health issue, affecting cognitive functions and academic performance for 8% of children. If LDs are not detected early and addressed through appropriate interventions, they have a heavy impact on these children in the social, educational, and professional spheres, at great cost to society. The BMT-i (Batterie Modulable de Tests informatisée, or "computerized Adaptable Test Battery") enables fast, easy, reliable assessments for each cognitive domain. It has previously been validated in children ages 4-13 who had no prior complaints. The present study demonstrates the sensitivity of the BMT-i, relative to reference test batteries, for 191 children with cognitive difficulties. Materials and Methods: These 191 subjects were included in the study by the 14 pediatricians treating them for complaints in five cognitive domains: written language [60 (cases)]; mathematical cognition (40); oral language (60); handwriting, drawing, and visuospatial construction (45); and attention and executive functioning (45). In accordance with a predefined protocol, the children were administered BMT-i tests first, by their pediatricians, and reference tests later, by specialists to whom the BMT-i test results were not disclosed. Comparison of BMT-i and reference test results made it possible to evaluate sensitivity and agreement between tests. Results: For each of the five domains, the BMT-i was very sensitive (0.91-1), and normal BMT-i results were highly predictive of normal results for specialized reference tests [negative likelihood ratio (LR-): 0-0.16]. There was close agreement between BMT-i and reference tests in all domains except attention and executive functioning, for which only moderate agreement was observed. Conclusion: The BMT-i offers rapid, reliable, simple computerized assessments whose sensitivity and agreement with reference test batteries make it a suitable first-line instrument for LD screening in children 4-13 years old.

The Computerized Adaptable Test Battery (BMT-i) for Rapid Assessment of Children's Academic Skills and Cognitive Functions: A Validation Study.

Background: Learning disabilities in children are a major public health concern worldwide, having a prevalence of 8%. They are associated with lost social, educational, and ultimately, professional opportunities for individuals. These disabilities are also very costly to governments and raise the issue of the appropriate means of screening. Unfortunately, validated tools for preliminary appraisal of learning and cognitive function in struggling children are presently restricted to specific age ranges and cognitive domains. This study sought to validate a first-line battery for assessment of academic skills and cognitive functions. Materials and Methods: The computerized Adaptable Test Battery, or BMT-i, includes a panel of tests for the first-line assessment of children's academic skills and cognitive functions. The tests reflect expected abilities for the age group in question, exploring academic skills (written language and mathematical cognition) and cognitive domains (verbal, non-verbal, and attentional/executive functions). The authors relied on the results of these tests for a sample of 1,074 Francophone children representative of the mainland French school-age population (522 boys and 552 girls, ages 4-13, from 39 classes at 7 public and 5 private schools). Thirteen speech-language pathologists and neuropsychologists individually administered the tests. Results: The psychometric characteristics of the empirical data obtained showed acceptable to good test homogeneity, internal consistency (Cronbach's alpha: > 0.70), test-retest reliability (intraclass correlation coefficients: ~0.80), and consistency with reference test batteries (r: 0.44-0.96). Conclusion: The BMT-i was validated in a large sample of children in mainstream French schools, paving the way for its use in first-line screening of learning disabilities among children with complaints, whether their learning difficulties have been flagged by their parents or by their teachers.

Do supine position and deprivation of visual environment influence spatial neglect?

It has been suggested that in spatial neglect, placing the patient in a supine position and performing tasks in the dark would reduce the rightward bias in line bisection and cancellation tasks. However, these findings remain debated and have not been extended to other tasks such as reading or visual exploration. Here, in the same study, we examined the effect of body position (BP) and visual environment (VE) on relatively ecological tests of spatial neglect. Among 17 patients with right-hemisphere stroke, 12 were neglect and five were non-neglect in clinical tests. They were compared with 12 healthy control participants in four tasks: line bisection, text reading, number reading, and visual exploration. Tasks were performed on a computer screen in two BP (sitting and supine) and two VE (light and dark) conditions. We found that placing patients in darkness reduced contralesional omissions in the visual exploratory task and, to a smaller extent, in number reading. Conversely, the supine position did not influence performance, and even resulted in cognitive slowing, especially in reading. In conclusion, we confirmed that reducing visual information can improve performance, but only to a limited extent. This justifies strict control of peripheral visual information when exploring neglect patients. Conversely, positioning neglect patients in the supine position can have a discrete negative effect on cognitive functioning, and this effect must be taken into account during therapy.