A specific deficit of dorsal stream function in Williams' syndrome

Developmental coordination disorder and cerebral visual impairment: What is the association?

INTRODUCTION

Children with Developmental Coordination Disorder (DCD) experience impairments beyond motor planning, affecting visual perceptual and visual-motor integration abilities, similar to children with Cerebral Visual Impairment (CVI), making it challenging to distinguish between the two conditions. This study aimed to identify convergences and divergences in the clinical, neuropsychological, and functional vision-related skills of children with DCD and CVI.

METHODS

An assessment of the neuropsychological profile (cognitive, visual cognitive, and motor coordination skills) and visual acuity were conducted on 65 children with DCD (mean age: 8 years, 1 month; SD: 1 year, 6 months) and 35 children with CVI (mean age: 8 years, 5 months; SD: 2 years, 6 months) and compared between the two groups. The CVI-Inventory (CVI-I) was used to evaluate functional vision-related problems and to cluster subjects.

RESULTS

Visual attention, visual perception, global motor coordination, and visual constructive scores didn't differ between the two groups even if children with CVI showed lower scores in the intellectual, visual, visual cognitive, and motor abilities. The overlap index confirmed an overlap on most of the variables considered. Six discriminative questions from the CVI-I clustered subjects into two groups: the first, with more children with CVI (62.9 %) and a more compromised neuropsychological profile, and the second, with more children with DCD (86.7 %).

CONCLUSION

DCD and CVI share both similarities and differences. Low visual acuity, low IQ scores, severe visual-motor integration challenges, and difficulties with fine motor and balance skills should prompt clinicians to screen for CVI in children with DCD. Specific functional vision-related problems can assist in this differentiation.

Narrative microstructure and macrostructure in adolescents with Down syndrome and Williams syndrome

Down syndrome (DS) and Williams syndrome (WS) are genetic neurodevelopmental disorders associated with intellectual disability, showing contrasting linguistic profiles with asymmetries in grammatical (DS weakness/WS strength) vs. pragmatic abilities (DS strength/WS weakness). The aim of the present study was to explore the linguistic profiles of 14 adolescents with DS and WS, and 14 typically developing controls (matched by chronological and verbal age) by comparing the microstructure and macrostructure of narratives and their possible dissociation. Participants watched an episode of the Tom and Jerry cartoon series and were asked to retell it. The videotaped narratives were transcribed and analyzed with the tools of the CHILDES Project and the Pragmatic Evaluation Protocol for Corpora (PREP-CORP). Microstructure was assessed by productivity at the grammatical level (number of utterances) and lexical level (number of word tokens), and complexity at the grammatical level (MLU) and lexical level (number of word types). Macrostructure was assessed by the number of story elements recalled at three levels: scenarios (global), episodes (integrated), and events (detailed). Results confirmed asymmetries in the linguistic profiles of both groups, with relative strengths of adolescents with DS in macrostructure despite relative weaknesses in microstructure. Conversely, adolescents with WS exhibited strengths in narrative microstructure, but failed to show better performance than the DS group in macrostructure. Following regression analyses, microstructure predicted macrostructure in typically developing adolescents, while no association was found between both levels in the profiles of adolescents with WS and DS, which was interpreted as an atypical dissociation.

Visuospatial memory in apraxia: Exploring quantitative drawing metrics to assess the representation of local and global information

Neuropsychological evidence suggests that visuospatial memory is subserved by two separable processing systems, with dorsal underpinnings for global form and ventral underpinnings for the integration of part elements. Previous drawing studies have explored the effects of Gestalt organisation upon memory for hierarchical stimuli, and we here present an exploratory study of an apraxic dorsal stream patient's (MH) performance. We presented MH with a stimulus set (previously reported by Riddoch et al., Cognitive Neuropsychology, 20(7), 641-671, 2003) and devised a novel quantitative scoring system to obtain a finer grain of insight into performance. Stimuli possessed either good or poor Gestalt qualities and were reproduced in a copy condition and two visual memory conditions (with unlimited viewing before the model was removed, or with 3 s viewing). MH's copying performance was impaired in comparison to younger adult and age-matched older adult controls, with a variety of errors at the local level but relatively few at the global level. However, his performance in the visual memory conditions revealed impairments at the global level. For all participants, drawing errors were modulated by the Gestalt qualities of the stimuli, with accuracy at the global and local levels being lesser for poor global stimuli in all conditions. These data extend previous observations of this patient, and support theories that posit interaction between dorsal and ventral streams in the representation of hierarchical stimuli. We discuss the implications of these findings for our understanding of visuospatial memory in neurological patients, and also evaluate the application of quantitative metrics to the interpretation of drawings.

News insights into social cognition in Williams syndrome from a comprehensive assessment and a virtual reality task

Although the uneven neuropsychological profile of William Syndrome (WS) is well established, less is known about social perception and how profile characteristics may affect the ability to predict other's intentions, a main hallmark of social cognition. This study aimed at examining the neuropsychological profile, including social perception, of adolescents and adults with WS, and at verifying which neuropsychological outcome might account for their social prediction ability. Twenty-six individuals with WS were administered a comprehensive neuropsychological assessment, and a virtual reality scenario designed to assess social prediction in a dynamic, everyday life-like context. We found that social perception was a relative strength of the profile, although a dissociation emerged between impaired verbal ToM and relatively spared low-level components. Peaks and valleys were reported in other domains consistently with the expected profile. Both spatial and facial memory were significantly associated with the performance at the social prediction task. Results clarified that social perception per se should not be considered as typically impaired in WS. Weaknesses and strengths in specific abilities, particularly spatial and facial memory, might affect the ability to understand others' intentions in WS beyond domain-specific mechanisms. These findings might inform future syndrome-specific rehabilitative interventions.

Development of Higher-Level Vision: A Network Perspective

Most studies on the development of the visual system have focused on the mechanisms shaping early visual stages up to the level of primary visual cortex (V1). Much less is known about the development of the stages after V1 that handle the higher visual functions fundamental to everyday life. The standard model for the maturation of these areas is that it occurs sequentially, according to the positions of areas in the adult hierarchy. Yet, the existing literature reviewed here paints a different picture, one in which the adult configuration emerges through a sequence of unique network configurations that are not mere partial versions of the adult hierarchy. In addition to studying higher visual development per se to fill major gaps in knowledge, it will be crucial to adopt a network-level perspective in future investigations to unravel normal developmental mechanisms, identify vulnerabilities to developmental disorders, and eventually devise treatments for these disorders.

Visual processing and decision-making in autism and dyslexia: Insights from cross-syndrome approaches

Atypical visual processing has been reported in developmental conditions like autism and dyslexia, and some accounts propose a causal role for visual processing in the development of these conditions. However, few studies make direct comparisons between conditions, or use sufficiently sensitive methods, meaning that it is hard to say whether atypical visual processing tells us anything specific about these conditions, or whether it reflects a more general marker of atypical development. Here I review findings from two computational modelling approaches (equivalent noise and diffusion modelling) and related electroencephalography (EEG) indices which we have applied to data from autistic, dyslexic and typically developing children to reveal how the component processes involved in visual processing and decision-making are altered in autism and dyslexia. The results identify both areas of convergence and divergence in autistic and dyslexic children's visual processing and decision-making, with implications for influential theoretical accounts such as weak central coherence, increased internal noise, and dorsal-stream vulnerability. In both sets of studies, we also see considerable variability across children in all three groups. To better understand this variability, and further understand the convergence and divergence identified between conditions, future studies would benefit from studying how the component processes reviewed here relate to transdiagnostic dimensions, which will also give insights into individual differences in visual processing and decision-making more generally.

Motion and Form Perception in Childhood-Onset Schizophrenia

(1) Background: Childhood-onset schizophrenia (COS) is a rare type of psychotic disorder characterized by delusions, hallucinations, grossly disorganized behavior, and poor psychosocial functioning. The etiology of COS is unknown, but neurodevelopmental factors are likely to play a critical role. A potential neurodevelopmental anomaly marker is the dorsal visual system dysfunction, which is implicated in motion perception, spatial functions, and attention. (2) Methods: To elucidate the role of the dorsal visual system in COS, we investigated 21 patients with COS and 21 control participants matched for age, sex, education, IQ, and parental socioeconomic status. Participants completed a motion and form coherence task, during which one assesses an individual's ability to detect the direction of motion within a field of moving elements or dots and to recognize a meaningful form or object from a set of fragmented or disconnected visual elements, respectively. (3) Results: The patients with COS were impaired in both visual tasks compared to the control participants, but the evidence for the deficit was more substantial for motion perception than for form perception (form: BF10 = 27.22; motion: BF10 = 6.97 × 106). (4) Conclusions: These results highlight the importance of dorsal visual stream vulnerability in COS, a potential marker of neurodevelopmental anomalies.

Dissociable Cognitive Systems for Recognizing Places and Navigating through Them: Developmental and Neuropsychological Evidence

Recent neural evidence suggests that the human brain contains dissociable systems for "scene categorization" (i.e., recognizing a place as a particular kind of place, for example, a kitchen), including the parahippocampal place area, and "visually guided navigation" (e.g., finding our way through a kitchen, not running into the kitchen walls or banging into the kitchen table), including the occipital place area. However, converging behavioral data - for instance, whether scene categorization and visually guided navigation abilities develop along different timelines and whether there is differential breakdown under neurologic deficit - would provide even stronger support for this two-scene-systems hypothesis. Thus, here we tested scene categorization and visually guided navigation abilities in 131 typically developing children between 4 and 9 years of age, as well as 46 adults with Williams syndrome, a developmental disorder with known impairment on "action" tasks, yet relative sparing on "perception" tasks, in object processing. We found that (1) visually guided navigation is later to develop than scene categorization, and (2) Williams syndrome adults are impaired in visually guided navigation, but not scene categorization, relative to mental age-matched children. Together, these findings provide the first developmental and neuropsychological evidence for dissociable cognitive systems for recognizing places and navigating through them.SIGNIFICANCE STATEMENT Two decades ago, Milner and Goodale showed us that identifying objects and manipulating them involve distinct cognitive and neural systems. Recent neural evidence suggests that the same may be true of our interactions with our environment: identifying places and navigating through them are dissociable systems. Here we provide converging behavioral evidence supporting this two-scene-systems hypothesis - finding both differential development and breakdown of "scene categorization" and "visually guided navigation." This finding suggests that the division of labor between perception and action systems is a general organizing principle for the visual system, not just a principle of the object processing system in particular.

Cognitive predictors of Social processing in congenital atypical development

According to current accounts of social cognition, the emergence of verbal and non-verbal components of social perception might rely on the acquisition of different cognitive abilities. These components might be differently sensitive to the pattern of neuropsychological impairments in congenital neurodevelopmental disorders. Here, we explored the association between social and non-social cognitive domains by administering subtests of the NEPSY-II battery to 92 patients with Intellectual and Developmental Disability (IDD). Regardless the level of intellectual functioning and presence of congenital brain malformations, results revealed that visuospatial skills predicted emotion recognition and verbal component of Theory of Mind, whereas imitation predicted the non-verbal one. Future interventions might focus on spatial and sensorimotor abilities to boost the development of social cognition in IDD.

Development of static and dynamic perception for luminance- and texture-defined information from school-ages to adulthood

Few studies have assessed the visual development of static and dynamic information processing at different levels of processing during typical development from the school-age years to adulthood. The implication of non-visual factors on visual development, such as cognitive (e.g., IQ) and attentional abilities, has yet to be systematically assessed with regard to spanning such a large age range. To address these voids, 203 typically-developing participants (aged 6 to 31 years) identified the orientation or direction of a static or moving grating defined by either luminance- or texture-contrast. An adaptive staircase procedure was used to measure contrast sensitivity in all four conditions. Cognitive (Wechsler IQ) and attentional ability (CPT-3) were also measured for all participants. Different developmental rates of contrast sensitivity were found between static and dynamic conditions when defined by more complex, texture-defined information, with the difference in sensitivity starting after the age of 9.71 years. However, static and dynamic profiles for luminance-defined information developed similarly with age. In addition, IQ did not correlate with nor predict the sensitivity across any condition. These results suggest age significantly explains the variance in the developmental profiles of contrast sensitivity above and beyond non-visual factors such as IQ and the CPT-3 attentional scores. Moreover, the neural pathways processing static and dynamic visual information continue to develop through late childhood and adolescence for the processing of texture-defined information only.

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

Dyslexic individuals have been reported to have reduced global motion sensitivity, which could be attributed to various causes including atypical magnocellular or dorsal stream function, impaired spatial integration, increased internal noise and/or reduced external noise exclusion. Here, we applied an equivalent noise experimental paradigm alongside a traditional motion-coherence task to determine what limits global motion processing in dyslexia. We also presented static analogues of the motion tasks (orientation tasks) to investigate whether perceptual differences in dyslexia were restricted to motion processing. We compared the performance of 48 dyslexic and 48 typically developing children aged 8 to 14 years in these tasks and used equivalent noise modelling to estimate levels of internal noise (the precision associated with estimating each element's direction/orientation) and sampling (the effective number of samples integrated to judge the overall direction/orientation). While group differences were subtle, dyslexic children had significantly higher internal noise estimates for motion discrimination, and higher orientation-coherence thresholds, than typical children. Thus, while perceptual differences in dyslexia do not appear to be restricted to motion tasks, motion and orientation processing seem to be affected differently. The pattern of results also differs from that previously reported in autistic children, suggesting perceptual processing differences are condition-specific.

Unilateral resection of both cortical visual pathways in a pediatric patient alters action but not perception

The human cortical visual system consists of two major pathways, a ventral pathway that subserves perception and a dorsal pathway that primarily subserves visuomotor control. Previous studies have found that children with cortical resections of the ventral visual pathway retain largely normal visuoperceptual abilities. Whether visually guided actions, supported by computations carried out by the dorsal pathway, follow a similar pattern of preservation remains unknown. To address this question, we examined visuoperceptual and visuomotor behaviors in a pediatric patient, TC, who underwent a cortical resection that included portions of the left ventral and dorsal pathways. We collected kinematic data when TC used her right and left hands to perceptually estimate the width of blocks that varied in width and length, and, separately, to grasp the same blocks. TC's perceptual estimation performance was comparable to that of controls, independent of the hand used. In contrast, relative to controls, she showed reduced visuomotor sensitivity to object shape and this was more evident when she grasped the objects with her contralesional right hand. These results provide novel evidence for a striking difference in the competence of the two visual pathways to cortical injuries acquired in childhood.

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.

Dorsal and Ventral Stream Function in Children With Developmental Coordination Disorder

Dorsal stream cortical networks underpin a cluster of visuomotor, visuospatial, and visual attention functions. Sensitivity to global coherence of motion and static form is considered a signature of visual cortical processing in the dorsal stream (motion) relative to the ventral stream (form). Poorer sensitivity to global motion compared to global static form has been found across a diverse range of neurodevelopmental disorders, suggesting a “dorsal stream vulnerability.” However, previous studies of global coherence sensitivity in Developmental Coordination Disorder (DCD) have shown conflicting findings. We examined two groups totalling 102 children with DCD (age 5–12 years), using the “Ball in the Grass” psychophysical test to compare sensitivity to global motion and global static form. Motor impairment was measured using the Movement-ABC (M-ABC). Global coherence sensitivity was compared with a typically developing control group (N = 69) in the same age range. Children with DCD showed impaired sensitivity to global motion (p = 0.002), but not global form (p = 0.695), compared to controls. Within the DCD group, motor impairment showed a significant linear relationship with global form sensitivity (p < 0.001). There was also a significant quadratic relationship between motor impairment and global motion sensitivity (p = 0.046), where poorer global motion sensitivity was only apparent with greater motor impairment. We suggest that two distinct visually related components, associated with global form and global motion sensitivity, contribute to DCD differentially over the range of severity of the disorder. Possible neural circuitry underlying these relationships is discussed.

Continuous theta burst TMS of area MT+ impairs attentive motion tracking

Attentive motion tracking deficits measured using multiple object tracking (MOT) tasks have been identified in a number of neurodevelopmental disorders such as amblyopia and autism. These deficits are often attributed to the abnormal development of high-level attentional networks. However, neuroimaging evidence from amblyopia suggests that reduced MOT performance can be explained by impaired function in motion-sensitive area MT+ alone. To test the hypothesis that a subtle disruption of MT+ function could cause MOT impairment, we assessed whether continuous theta burst stimulation (cTBS) of MT+ influenced MOT task accuracy in individuals with normal vision. The MOT stimulus consisted of four target and four distractor dots and was presented at ±10° eccentricity (right/left hemifield). fMRI-guided cTBS was applied to left MT+. Participants (n = 13, age: 27 ± 3) attended separate active and sham cTBS sessions where the MOT task was completed before, 5-min post- and 30-min post-cTBS. Active cTBS significantly impaired MOT task accuracy relative to baseline for the right (stimulated) hemifield 5-min (10 ± 2% reduction) and 30-min (14 ± 3% reduction) post-stimulation. No impairment occurred within the left (control) hemifield after active cTBS or for either hemifield after sham cTBS. These results highlight the importance of lower level motion processing for MOT, suggesting that a minor disruption of MT+ function alone is sufficient to cause a deficit in MOT performance.

A Critical Review of Spatial Abilities in Down and Williams Syndromes: Not All Space Is Created Equal

Down syndrome (DS, Trisomy 21) and Williams syndrome (WS) are two neurodevelopmental disorders of genetic origin that are accompanied by mild to moderate intellectual disability but exhibit distinct cognitive profiles. In this review we discuss our recent work characterizing the real-world spatial learning and memory abilities of adult individuals with DS and WS. We used several different paradigms in which participants locomote freely and have access to coherent input from all sensory modalities to investigate their fundamental egocentric (body-centered or viewpoint-dependent) and allocentric (world-centered or viewpoint-independent) spatial abilities. We found unequivocal evidence that most individuals with DS exhibit low-resolution egocentric and allocentric spatial learning and memory abilities similar to typically developing (TD) children in the same mental age range. In contrast, most individuals with DS exhibit impaired high-resolution allocentric spatial learning and facilitated response learning as compared to TD children. In comparison, whereas most individuals with WS also exhibit facilitated response learning, their low-resolution allocentric spatial learning and memory abilities are severely impaired as compared to both TD children and individuals with DS. Together with work from other laboratories using real-world or virtual reality paradigms, these findings indicate that in order to navigate in their environment most individuals with DS may use either egocentric route learning that does not integrate individual landmarks, or a low-resolution allocentric spatial representation that encodes the relationships between different locations (i.e., cognitive mapping). In contrast, since most individuals with WS are unable to build or use a low-resolution allocentric or configural representation of the environment they may use visually and verbally encoded landmarks as beacons to learn routes. Finally, we discuss the main neural structures implicated in these different spatial processes and explain how the relative preservation or impairment of specific brain functions may engender the unique cognitive profiles observed in individuals with these neurodevelopmental disorders.

Cognitive, behavioral, and social functioning in children and adults with Dravet syndrome

AIM

The objective of the study was to delineate the cognitive, behavioral, psychological, and social functioning of individuals with Dravet syndrome.

METHOD

Cognitive, behavioral, and social functioning were assessed in patients with Dravet syndrome by comprehensive, age-appropriate standardized neuropsychological testing. Primary caregivers completed standardized measures regarding participants' behavior, psychological status, adaptive functioning, and social skills, including their involvement with intervention services.

RESULTS

The cohort comprised 45 patients, aged 2-30 years. Intellectual functioning ranged from average intellect to profound intellectual disability, with a decrease in cognitive and adaptive functioning with age. Only 6 children were able to complete the entire neuropsychological battery and showed a range of cognitive profiles. Five of 6 participants scored within the average range on Affect Recognition and 5/6 on Motor Free Visual Perception tests. Twenty-one (58%) participants had deficits in social skills and 18/27 (67%) in social communication, with 10 participants, who did not yet have a diagnosis of autism spectrum disorder (ASD), screening positive for social communication deficits. Behavioral problems were frequently reported, with attention problems in 24 (65%) and atypicality in 25 (70%). Despite this, parents reported that psychological services were the least utilized health interventions.

CONCLUSIONS

Cognitive functioning varies markedly in individuals with Dravet syndrome, with some patients demonstrating global impairment while others have a discordant neuropsychological profile. Behavioral, psychological, social problems, and ASD are common. Social deficits should be reviewed to identify those who warrant ASD assessment. Early identification of behavioral and psychological disorders and targeted use of psychological intervention are essential components of holistic care in Dravet syndrome.

Characterizing the neural signature of face processing in Williams syndrome via multivariate pattern analysis and event related potentials

Face recognition ability is often reported to be a relative strength in Williams syndrome (WS). Yet methodological issues associated with the supporting research, and evidence that atypical face processing mechanisms may drive outcomes 'in the typical range', challenge these simplistic characterisations of this important social ability. Detailed investigations of face processing abilities in WS both at a behavioural and neural level provide critical insights. Here, we behaviourally characterised face recognition ability in 18 individuals with WS comparatively to typically developing children and adult control groups. A subset of 11 participants with WS as well as chronologically age matched typical adults further took part in an EEG task where they were asked to attentively view a series of upright and inverted faces and houses. State-of-the-art multivariate pattern analysis (MVPA) was used alongside standard ERP analysis to obtain a detailed characterisation of the neural profile associated with 1) viewing faces as an overall category (by examining neural activity associated with upright faces and houses), and to 2) the canonical upright configuration of a face, critically associated with expertise in typical development and often linked with holistic processing (upright and inverted faces). Our results show that while face recognition ability is not on average at a chronological age-appropriate level in individuals with WS, it nonetheless appears to be a relative strength within their cognitive profile. Furthermore, all participants with WS revealed a differential pattern of neural activity to faces compared to objects, showing a distinct response to faces as a category, as well as a differential neural pattern for upright vs. inverted faces. Nonetheless, an atypical profile of face orientation classification was found in WS, suggesting that this group differs from typical individuals in their face processing mechanisms. Through this innovative application of MVPA, alongside the high temporal resolution of EEG, we provide important new insights into the neural processing of faces in WS.

Visual development

The developing visual brain is an integrated system, linking analysis of the visual input to visuomotor control, visual cognition, and attention. Major points in human visual development are the presence of rudimentary pathways present at birth which can control fixation behavior, with subsequent development of specific functions. These functions include the emergence of cortical selectivity; the integration of local signals to provide global representations of motion, shape, and space; the development of visuomotor modules for eye movements, manual reaching, and locomotion; and the development of distinct attentional systems. Measures of these processes in infancy and early childhood can provide indicators of broader brain development in the at-risk child. A key system in development is the dorsal cortical stream. Measures of global motion processing, visuomotor actions, and attention suggest that this system is particularly vulnerable in children with a wide range of neurodevelopmental disorders. Early disorders of the eye (strabismus, cataract) reveal the level of plasticity in the developing visual system and the ways in which early experience can affect the course of functional development.

Neural dynamics underlying coherent motion perception in children and adults

Motion sensitivity increases during childhood, but little is known about the neural correlates. Most studies investigating children's evoked responses have not dissociated direction-specific and non-direction-specific responses. To isolate direction-specific responses, we presented coherently moving dot stimuli preceded by incoherent motion, to 6- to 7-year-olds (n = 34), 8- to 10-year-olds (n = 34), 10- to 12-year-olds (n = 34) and adults (n = 20). Participants reported the coherent motion direction while high-density EEG was recorded. Using a data-driven approach, we identified two stimulus-locked EEG components with distinct topographies: an early component with an occipital topography likely reflecting sensory encoding and a later, sustained positive component over centro-parietal electrodes that we attribute to decision-related processes. The component waveforms showed clear age-related differences. In the early, occipital component, all groups showed a negativity peaking at ˜300 ms, like the previously reported coherent-motion N2. However, the children, unlike adults, showed an additional positive peak at ˜200 ms, suggesting differential stimulus encoding. The later positivity in the centro-parietal component rose more steeply for adults than for the youngest children, likely reflecting age-related speeding of decision-making. We conclude that children's protracted development of coherent motion sensitivity is associated with maturation of both early sensory and later decision-related processes.

The effect of mild traumatic brain injury on the visual processing of global form and motion

Cortical visual processing involves the ventral stream (form perception) and the dorsal stream (motion perception). We assessed whether mild traumatic brain injury (TBI) differentially affects these two streams. Eleven adults with mild TBI (28 ± 9 yrs, 17 ± 5 months post injury) and 25 controls (25 ± 5 yrs) participated. Participants completed tests of global processing involving Glass patterns (form) and random dot kinematograms (motion), measurement of contrast thresholds for motion direction discrimination, a comprehensive vision screening and the Post-Concussion Symptom Inventory (PCSI). Our results showed that the mild TBI group had significantly higher (worse) global form (mean ± SD: TBI 25 ± 6%, control 21 ± 5%) and motion (TBI 14 ± 7%, control 11 ± 3%) coherence thresholds than controls. The magnitude of the mild TBI group deficit did not differ between the two tasks. Contrast thresholds for motion direction discrimination did not differ between the groups, but were positively correlated with PCSI score (r² = 0.51. p = 0.01) in the mild TBI group. The mild TBI group had worse outcomes than controls for all clinical measurements of vision except distance visual acuity. In conclusion, mild TBI affects processing in both the dorsal and ventral cortical processing streams equally. In addition, spatiotemporal contrast sensitivity may be related to the symptoms of mild TBI.

Object complexity modulates the association between action and perception in childhood

Vision for action and vision for perception both rely on shape representations derived within the visual system. Whether the same psychological and neural mechanisms underlie both forms of behavior remains hotly contested, and whether this arrangement is equivalent in adults and children is controversial as well. To address these outstanding questions, we used an established psychophysical heuristic, Weber's law, which, in adults, has typically been observed for perceptual judgment tasks but not for actions such as grasping. We examined whether this perception-action dissociation in Weber's law was present in childhood as it is in adulthood and whether it was modulated by stimulus complexity. Two major results emerged. First, although adults evinced visuomotor behavior that violated Weber's law, young children (4.5-6.5 years) adhered to Weber's law when they grasped complex objects ("Efron" blocks), which varied along both the graspable and non-graspable dimensions to maintain a constant surface area, but not when they grasped simple objects, which varied only along the graspable dimension. Second, adherence to Weber's law was found across all ages in the context of a perceptual task. Together, these findings suggest that, in early childhood, visuomotor representations are modulated by perceptual representations, particularly when a refined description of object shape is needed.

Dyslexia and dyscalculia are characterized by common visual perception deficits

A number of studies have investigated the cognitive deficits underlying dyslexia and dyscalculia. Yet, it remains unclear as to whether dyslexia and dyscalculia are associated with the common visual perception deficits. The current investigation analyzed cognitive performance in children with dyslexia, dyscalculia, comorbidity, and typically developing subjects. The results showed that children with dyslexia, dyscalculia and comorbidity exhibited common deficits in numerosity processing and visual perception. Furthermore, visual perception deficits accounted for deficits in numerosity processing in all three groups. The results suggest that visual perception deficits are a common cognitive deficit underlying both developmental dyslexia and dyscalculia.

Evolutionary perspective on sex differences in the expression of neurological diseases

Sex-specific brain and cognitive deficits emerge with malnutrition, some infectious and neurodegenerative diseases, and often with prenatal or postnatal toxin exposure. These deficits are described in disparate literatures and are generally not linked to one another. Sexual selection may provide a unifying framework that integrates our understanding of these deficits and provides direction for future studies of sex-specific vulnerabilities. Sexually selected traits are those that have evolved to facilitate competition for reproductive resources or that influence mate choices, and are often larger and more complex than other traits. Critically, malnutrition, disease, chronic social stress, and exposure to man-made toxins compromise the development and expression of sexually selected traits more strongly than that of other traits. The fundamental mechanism underlying vulnerability might be the efficiency of mitochondrial energy capture and control of oxidative stress that in turn links these traits to current advances in neuroenergetics, stress endocrinology, and toxicology. The key idea is that the elaboration of these cognitive abilities, with more underlying gray matter or more extensive inter-modular white matter connections, makes them particularly sensitive to disruptions in mitochondrial functioning and oxidative stress. A framework of human sexually selected cognitive abilities and underlying brain systems is proposed and used to organize what is currently known about sex-specific vulnerabilities.

An fMRI study of coherent visual motion processing in children and adults

There is a large corpus of brain imaging studies examining the dorsal visual pathway, especially area V5/MT during visual motion perception. However, despite evidence suggesting a protracted development of the dorsal visual stream, and a role of this pathway in neurodevelopmental disorders, V5/MT has not been characterized developmentally. Further, experiential factors such as reading acquisition may play a modulating role in any age-dependent changes. Here we used a coherent visual motion detection task to examine V5/MT activity and connectivity in typical participants in two studies: a Cross- Sectional Study comparing adults and children; and a Longitudinal Study of 2nd graders followed into 3rd grade. In the Cross-Sectional Study, a whole-brain analysis revealed no differences between the two groups, whereas a region of interest (ROI) approach identified greater activation in left (right trending) V5/MT in adults compared to children. However, when we measured V5/MT activation individually for each participant, children and adults showed no difference in the location or intensity of activation, although children did exhibit relatively larger extent of V5/MT activation bilaterally. There was also relatively greater functional connectivity in the children between left and right occipitotemporal cortex, including V5/MT. The Longitudinal Study revealed no changes in V5/MT activation for any measures of activation or functional connectivity from 2nd to 3rd grade. Finally, there was no evidence of an association between reading and V5/MT over time, nor predictive power of V5/MT activity for later reading. Together, our results indicate similar V5/MT activity across age groups, with relatively greater extent of V5/MT activation and functional connectivity in children relative to adults, bilaterally. These differences were not apparent over the time course of one year, suggesting that these developmental changes occur over a more protracted period.

Learning by observation and learning by doing in Down and Williams syndromes

New skills may be learned by active experience (experiential learning or learning by doing) or by observation of others' experience (learning by observation). In general, learning by observation reduces the time and the attempts needed to learn complex actions and behaviors. The present research aimed to compare learning by observation and learning by doing in two clinical populations with different etiology of intellectual disability (ID), as individuals with Down syndrome (DS) and individuals with Williams syndrome (WS), with the hypothesis that specific profiles of learning may be found in each syndrome. To this end, we used a mixture of new and existing data to compare the performances of 24 individuals with DS, 24 individuals with WS and 24 typically developing children on computerized tasks of learning by observation or learning by doing. The main result was that the two groups with ID exhibited distinct patterns of learning by observation. Thus, individuals with DS were impaired in reproducing the previously observed visuo-motor sequence, while they were as efficient as TD children in the experiential learning task. On the other hand, individuals with WS benefited from the observational training while they were severely impaired in detecting the visuo-motor sequence in the experiential learning task (when presented first). The present findings reinforce the syndrome-specific hypothesis and the view of ID as a variety of conditions in which some cognitive functions are more disrupted than others because of the differences in genetic profile and brain morphology and functionality. These findings have important implications for clinicians, who should take into account the genetic etiology of ID in developing learning programs for treatment and education.

Increased glia density in the caudate nucleus in williams syndrome: Implications for frontostriatal dysfunction in autism

Williams syndrome (WS) is a rare neurodevelopmental disorder with a well-described, known genetic etiology. In contrast to Autism Spectrum Disorders (ASD), WS has a unique phenotype characterized by global reductions in IQ and visuospatial ability, with relatively preserved language function, enhanced reactivity to social stimuli and music, and an unusual eagerness to interact socially with strangers. A duplication of the deleted region in WS has been implicated in a subset of ASD cases, defining a spectrum of genetic and behavioral variation at this locus defined by these opposite extremes in social behavior. The hypersociability characteristic of WS may be linked to abnormalities of frontostriatal circuitry that manifest as deficits in inhibitory control of behavior. Here, we examined the density of neurons and glia in associative and limbic territories of the striatum including the caudate, putamen, and nucleus accumbens regions in Nissl stained sections in five pairs of age, sex, and hemisphere-matched WS and typically-developing control (TD) subjects. In contrast to what is reported in ASD, no significant increase in overall neuron density was observed in this study. However, we found a significant increase in the density of glia in the dorsal caudate nucleus, and in the ratio of glia to neurons in the dorsal and medial caudate nucleus in WS, accompanied by a significant increase in density of oligodendrocytes in the medial caudate nucleus. These cellular abnormalities may underlie reduced frontostriatal activity observed in WS, with implications for understanding altered connectivity and function in ASD. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 531-545, 2018.

Dissociating intuitive physics from intuitive psychology: Evidence from Williams syndrome

Prior work suggests that our understanding of how things work ("intuitive physics") and how people work ("intuitive psychology") are distinct domains of human cognition. Here we directly test the dissociability of these two domains by investigating knowledge of intuitive physics and intuitive psychology in adults with Williams syndrome (WS) - a genetic developmental disorder characterized by severely impaired spatial cognition, but relatively spared social cognition. WS adults and mental-age matched (MA) controls completed an intuitive physics task and an intuitive psychology task. If intuitive physics is a distinct domain (from intuitive psychology), then we should observe differential impairment on the physics task for individuals with WS compared to MA controls. Indeed, adults with WS performed significantly worse on the intuitive physics than the intuitive psychology task, relative to controls. These results support the hypothesis that knowledge of the physical world can be disrupted independently from knowledge of the social world.

New insights into the role of motion and form vision in neurodevelopmental disorders

A selective deficit in processing the global (overall) motion, but not form, of spatially extensive objects in the visual scene is frequently associated with several neurodevelopmental disorders, including preterm birth. Existing theories that proposed to explain the origin of this visual impairment are, however, challenged by recent research. In this review, we explore alternative hypotheses for why deficits in the processing of global motion, relative to global form, might arise. We describe recent evidence that has utilised novel tasks of global motion and global form to elucidate the underlying nature of the visual deficit reported in different neurodevelopmental disorders. We also examine the role of IQ and how the sex of an individual can influence performance on these tasks, as these are factors that are associated with performance on global motion tasks, but have not been systematically controlled for in previous studies exploring visual processing in clinical populations. Finally, we suggest that a new theoretical framework is needed for visual processing in neurodevelopmental disorders and present recommendations for future research.

Motion Perception and Form Discrimination in Extremely Preterm School-Aged Children

This population-based study evaluated motion and form perception in 71 children born extreme premature (EPT; < 27 gestational weeks), aged 6.5 years, as compared to a matched group of 79 control children born at term. Motion and form perception were evaluated by motion coherence and form coherence tests. The EPT group showed a poorer performance on both tasks as compared to the control group. However, after controlling for IQ and visual acuity, the EPT group showed only a significant deficit in motion perception. No association was found between motion perception accuracy and gestational age, previous retinopathy of prematurity, or previous intraventricular hemorrhage in the EPT group. The results highlight the long-term motion perception deficits in children born EPT.

Visual perception skills: a comparison between patients with Noonan syndrome and 22q11.2 deletion syndrome

Ventral and dorsal streams are visual pathways deputed to transmit information from the photoreceptors of the retina to the lateral geniculate nucleus and then to the primary visual cortex (V1). Several studies investigated whether one pathway is more vulnerable than the other during development, and whether these streams develop at different rates. The results are still discordant. The aim of the present study was to understand the functionality of the dorsal and the ventral streams in two populations affected by different genetic disorders, Noonan syndrome (NS) and 22q11.2 deletion syndrome (22q11.2DS), and explore the possible genotype-phenotype relationships. 'Form coherence' abilities for the ventral stream and 'motion coherence' abilities for the dorsal stream were evaluated in 19 participants with NS and 20 participants with 22q11.2DS. Collected data were compared with 55 age-matched controls. Participants with NS and 22q11.2DS did not differ in the form coherence task, and their performance was significantly lower than that of controls. However, in the motion coherence task, the group with NS and controls did not differ, and both obtained significantly higher scores than the group with 22q11.2DS. Our findings indicate that deficits in the dorsal stream are related to the specific genotype, and that in our syndromic groups the ventral stream is more vulnerable than the dorsal stream.

Where is the 'subjective straight ahead' in Williams syndrome?

BACKGROUND

Individuals with Williams Syndrome (WS) are known to have particular difficulties when performing visuo-spatial tasks, which could be related to their difficulties in using a specific reference system to determine spatial relations. The aim of the present study was to assess the internal representation of the body's sagittal plane, which is an important benchmark for an egocentric frame of reference.

METHOD

The results of 18 WS individuals (mean age = 20.5 ± 9.2 years) on the subjective straight ahead (SSA) task were compared with those of two healthy control groups composed of 36 participants matched on chronological age matched on chronological age (CA) and 30 young children matched on non-verbal intellectual ability (YC).

RESULTS

Individuals with WS showed a significant left deviation on the SSA body's sagittal plane representation compared with the chronological age control group and a marginal left deviation compared with the young children control group. A comparison with the objective SA (0°) showed a significant leftward deviation in the WS group but not in the two control groups.

CONCLUSIONS

Individuals with WS showed a significant leftward deviation in the SSA task. This bias of the body's longitudinal axe representation could have a negative impact on the use of an egocentric reference system, which could be the cause for their difficulties in defining spatial relations (e.g. location and orientation) necessary for performing spatial tasks.

Global motion perception is related to motor function in 4.5-year-old children born at risk of abnormal development

Global motion perception is often used as an index of dorsal visual stream function in neurodevelopmental studies. However, the relationship between global motion perception and visuomotor control, a primary function of the dorsal stream, is unclear. We measured global motion perception (motion coherence threshold; MCT) and performance on standardized measures of motor function in 606 4.5-year-old children born at risk of abnormal neurodevelopment. Visual acuity, stereoacuity and verbal IQ were also assessed. After adjustment for verbal IQ or both visual acuity and stereoacuity, MCT was modestly, but significantly, associated with all components of motor function with the exception of fine motor scores. In a separate analysis, stereoacuity, but not visual acuity, was significantly associated with both gross and fine motor scores. These results indicate that the development of motion perception and stereoacuity are associated with motor function in pre-school children.

Effect of spatial and temporal stimulus parameters on the maturation of global motion perception

There are discrepancies with respect to the age at which adult-like performance is reached on tasks assessing global motion perception. This is in part because performance in children depends on stimulus parameters. We recently showed that five-year-olds demonstrated adult-like performance over a range of speeds when the speed ratio was comprised of longer spatial and temporal displacements; but displayed immature performance when the speed ratio was comprised of shorter displacements. The goal of the current study was to assess the effect of these global motion stimulus parameters across a broader age range in order to estimate the age at which mature performance is reached. Motion coherence thresholds were assessed in 182 children and adults aged 7-30years. Dot displacement (Δx) was 1, 5, or 30min of arc; frame duration (Δt) was 17 or 50ms. This created a total of six conditions. Consistent with our previous results, coherence thresholds in the youngest children assessed were adult-like at the two conditions with the largest Δx. Maturity was reached around age 12 for the medium Δx, and by age 16 for the smallest Δx. Performance did not appear to be affected by Δt. This late maturation may reflect a long developmental period for cortical networks underlying global motion perception. These findings resolve many of the discrepancies across previous studies, and should be considered when using global motion tasks to assess children with atypical development.

Different trajectories of decline for global form and global motion processing in aging, mild cognitive impairment and Alzheimer's disease

The visual processing of complex motion is impaired in Alzheimer's disease (AD). However, it is unclear whether these impairments are biased toward the motion stream or part of a general disruption of global visual processing, given some reports of impaired static form processing in AD. Here, for the first time, we directly compared the relative preservation of motion and form systems in AD, mild cognitive impairment, and healthy aging, by measuring coherence thresholds for well-established global rotational motion and static form stimuli known to be of equivalent complexity. Our data confirm a marked motion-processing deficit specific to some AD patients, and greater than any form-processing deficit for this group. In parallel, we identified a more gradual decline in static form recognition, with thresholds raised in mild cognitive impairment patients and slightly further in the AD group compared with controls. We conclude that complex motion processing is more vulnerable to decline in dementia than complex form processing, perhaps owing to greater reliance on long-range neural connections heavily targeted by AD pathology.

The Davida Teller Award Lecture, 2016: Visual Brain Development: A review of "Dorsal Stream Vulnerability"-motion, mathematics, amblyopia, actions, and attention

Research in the Visual Development Unit on "dorsal stream vulnerability' (DSV) arose from research in two somewhat different areas. In the first, using cortical milestones for local and global processing from our neurobiological model, we identified cerebral visual impairment in infants in the first year of life. In the second, using photo/videorefraction in population refractive screening programs, we showed that infant spectacle wear could reduce the incidence of strabismus and amblyopia, but many preschool children, who had been significantly hyperopic earlier, showed visuo-motor and attentional deficits. This led us to compare developing dorsal and ventral streams, using sensitivity to global motion and form as signatures, finding deficits in motion sensitivity relative to form in children with Williams syndrome, or perinatal brain injury in hemiplegia or preterm birth. Later research showed that this "DSV" was common across many disorders, both genetic and acquired, from autism to amblyopia. Here, we extend DSV to be a cluster of problems, common to many disorders, including poor motion sensitivity, visuo-motor spatial integration for planning actions, attention, and number skills. In current research, we find that individual differences in motion coherence sensitivity in typically developing children are correlated with MRI measures of area variations in parietal lobe, fractional anisotropy (from TBSS) of the superior longitudinal fasciculus, and performance on tasks of mathematics and visuo-motor integration. These findings suggest that individual differences in motion sensitivity reflect decision making and attentional control rather than integration in MT/V5 or V3A. Its neural underpinnings may be related to Duncan's "multiple-demand" (MD) system.

Individual differences in children's global motion sensitivity correlate with TBSS-based measures of the superior longitudinal fasciculus

Reduced global motion sensitivity, relative to global static form sensitivity, has been found in children with many neurodevelopmental disorders, leading to the "dorsal stream vulnerability" hypothesis (Braddick et al., 2003). Individual differences in typically developing children's global motion thresholds have been shown to be associated with variations in specific parietal cortical areas (Braddick et al., 2016). Here, in 125 children aged 5-12years, we relate individual differences in global motion and form coherence thresholds to fractional anisotropy (FA) in the superior longitudinal fasciculus (SLF), a major fibre tract communicating between parietal lobe and anterior cortical areas. We find a positive correlation between FA of the right SLF and individual children's sensitivity to global motion coherence, while FA of the left SLF shows a negative correlation. Further analysis of parietal cortical area data shows that this is also asymmetrical, showing a stronger association with global motion sensitivity in the left hemisphere. None of these associations hold for an analogous measure of global form sensitivity. We conclude that a complex pattern of structural asymmetry, including the parietal lobe and the superior longitudinal fasciculus, is specifically linked to the development of sensitivity to global visual motion. This pattern suggests that individual differences in motion sensitivity are primarily linked to parietal brain areas interacting with frontal systems in making decisions on integrated motion signals, rather than in the extra-striate visual areas that perform the initial integration. The basis of motion processing deficits in neurodevelopmental disorders may depend on these same structures.

Visual memory profile in 22q11.2 microdeletion syndrome: are there differences in performance and neurobiological substrates between tasks linked to ventral and dorsal visual brain structures? A cross-sectional and longitudinal study

Background

Children affected by the 22q11.2 deletion syndrome (22q11.2DS) have a specific neuropsychological profile with strengths and weaknesses in several cognitive domains. Specifically, previous evidence has shown that patients with 22q11.2DS have more difficulties memorizing faces and visual-object characteristics of stimuli. In contrast, they have better performance in visuo-spatial memory tasks. The first focus of this study was to replicate these results in a larger sample of patients affected with 22q11.2DS and using a range of memory tasks. Moreover, we analyzed if the deficits were related to brain morphology in the structures typically underlying these abilities (ventral and dorsal visual streams). Finally, since the longitudinal development of visual memory is not clearly characterized in 22q11.2DS, we investigated its evolution from childhood to adolescence.

Methods

Seventy-one patients with 22q11.2DS and 49 control individuals aged between 9 and 16 years completed the Benton Visual Retention Test (BVRT) and specific subtests assessing visual memory from the Children’s Memory Scale (CMS). The BVRT was used to compute spatial and object memory errors. For the CMS, specific subtests were classified into ventral, dorsal, and mixed subtests. Longitudinal data were obtained from a subset of 26 patients and 22 control individuals.

Results

Cross-sectional results showed that patients with 22q11.2DS were impaired in all visual memory measures, with stronger deficits in visual-object memory and memory of faces, compared to visuo-spatial memory. No correlations between morphological brain impairments and visual memory were found in patients with 22q11.2DS. Longitudinal findings revealed that participants with 22q11.2DS made more object memory errors than spatial memory errors at baseline. This difference was no longer significant at follow-up.

Conclusions

Individuals with 22q11.2DS have impairments in visual memory abilities, with more pronounced difficulties in memorizing faces and visual-object characteristics. From childhood to adolescence, the visual cognitive profile of patients with 22q11.2DS seems globally stable even though some processes show an evolution with time. We hope that our results will help clinicians and caregivers to better understand the memory difficulties of young individuals with 22q11.2DS. This has a particular importance at school to facilitate recommendations concerning intervention strategies for these young patients.

Why is the processing of global motion impaired in adults with developmental dyslexia?

Individuals with dyslexia are purported to have a selective dorsal stream impairment that manifests as a deficit in perceiving visual global motion relative to global form. However, the underlying nature of the visual deficit in readers with dyslexia remains unclear. It may be indicative of a difficulty with motion detection, temporal processing, or any task that necessitates integration of local visual information across multiple dimensions (i.e. both across space and over time). To disentangle these possibilities we administered four diagnostic global motion and global form tasks to a large sample of adult readers (N=106) to characterise their perceptual abilities. Two sets of analyses were conducted. First, to investigate if general reading ability is associated with performance on the visual tasks across the entire sample, a composite reading score was calculated and entered into a series of continuous regression analyses. Next, to investigate if the performance of readers with dyslexia differs from that of good readers on the visual tasks we identified a group of forty-three individuals for whom phonological decoding was specifically impaired, consistent with the dyslexic profile, and compared their performance with that of good readers who did not exhibit a phonemic deficit. Both analyses yielded a similar pattern of results. Consistent with previous research, coherence thresholds of poor readers were elevated on a random-dot global motion task and a spatially one-dimensional (1-D) global motion task, but no difference was found on a static global form task. However, our results extend those of previous studies by demonstrating that poor readers exhibited impaired performance on a temporally-defined global form task, a finding that is difficult to reconcile with the dorsal stream vulnerability hypothesis. This suggests that the visual deficit in developmental dyslexia does not reflect an impairment detecting motion per se. It is better characterised as a difficulty processing temporal information, which is exacerbated when local visual cues have to be integrated across multiple (>2) dimensions.

Speechreading Skill and Visual Movement Sensitivity are Related in Deaf Speechreaders

Individual speechreading abilities have been linked with a range of cognitive and language-processing factors. The role of specifically visual abilities in relation to the processing of visible speech is less studied. Here we report that the detection of coherent visible motion in random-dot kinematogram displays is related to speechreading skill in deaf, but not in hearing, speechreaders. A control task requiring the detection of visual form showed no such relationship. Additionally, people born deaf were better speechreaders than hearing people on a new test of silent speechreading.

Visual Form-Processing Deficits in Autism

People with autism have a number of reported deficits in object recognition and global processing. Is there a low-level spatial integration deficit associated with this? We measured spatial-form-coherence detection thresholds using a Glass stimulus in a field of random dots, and compared performance to a similar motion-coherence task. A coherent visual patch was depicted by dots separated by a rotational transformation in space (form) or space - time (motion). To measure parallel visual integration, stimuli were presented for only 250 ms. We compared detection thresholds for children with autism, children with Asperger syndrome, and a matched control group. Children with autism showed a significant form-coherence deficit and a significant motion-coherence deficit, while the performance of the children with Asperger syndrome did not differ significantly from that of controls on either task.

Cortical processing of global form, motion and biological motion under low light levels

Advances in potential treatments for rod and cone dystrophies have increased the need to understand the contributions of rods and cones to higher-level cortical vision. We measured form, motion and biological motion coherence thresholds and EEG steady-state visual evoked potentials (SSVEP) responses under light conditions ranging from photopic to scotopic. Low light increased thresholds for all three kinds of stimuli; however, global form thresholds were relatively more impaired than those for global motion or biological motion. SSVEP responses to coherent global form and motion were reduced in low light, and motion responses showed a shift in topography from the midline to more lateral locations. Contrast sensitivity measures confirmed that basic visual processing was also affected by low light. However, comparison with contrast sensitivity function (CSF) reductions achieved by optical blur indicated that these were insufficient to explain the pattern of results, although the temporal properties of the rod system may also play a role. Overall, mid-level processing in extra-striate areas is differentially affected by light level, in ways that cannot be explained in terms of low-level spatiotemporal sensitivity. A topographical shift in scotopic motion SSVEP responses may reflect either changes to inhibitory feedback mechanisms between V1 and extra-striate regions or a reduction of input to the visual cortex. These results provide insight into how higher-level cortical vision is normally organised in absence of cone input, and provide a basis for comparison with patients with cone dystrophies, before and after treatments aiming to restore cone function.

Face repetition detection and social interest: An ERP study in adults with and without Williams syndrome

The present study examined possible neural mechanisms underlying increased social interest in persons with Williams syndrome (WS). Visual event-related potentials (ERPs) during passive viewing were used to compare incidental memory traces for repeated vs. single presentations of previously unfamiliar social (faces) and nonsocial (houses) images in 26 adults with WS and 26 typical adults. Results indicated that participants with WS developed familiarity with the repeated faces and houses (frontal N400 response), but only typical adults evidenced the parietal old/new effect (previously associated with stimulus recollection) for the repeated faces. There was also no evidence of exceptional salience of social information in WS, as ERP markers of memory for repeated faces vs. houses were not significantly different. Thus, while persons with WS exhibit behavioral evidence of increased social interest, their processing of social information in the absence of specific instructions may be relatively superficial. The ERP evidence of face repetition detection in WS was independent of IQ and the earlier perceptual differentiation of social vs. nonsocial stimuli. Large individual differences in ERPs of participants with WS may provide valuable information for understanding the WS phenotype and have relevance for educational and treatment purposes.

Disorders of early language development in Dravet syndrome

The aim of this study was to investigate language disorders prospectively in patients with Dravet syndrome (DS) during the first years of life in order to identify their features and possibly the underlying mechanisms of the disease. At the Child Neurology Unit of Catholic University in Rome (Italy), thirteen patients with typical findings of DS were enrolled in the study. Full clinical observations, including neurological examination and long-term EEG monitoring, were prospectively and serially performed until a mean of 6years of age (range: 4years to 7years and 8months). The epileptic history was also collected in each case. In particular, developmental, cognitive, and detailed language assessments were performed with different tests according to the age of the patient. In addition to cognitive decline, characteristic language impairment was also found with a relative preservation of receptive abilities (comprehension) and a strong impairment of productive skills. This defect in sensorimotor verbal processing integration is discussed to highlight the possible mechanisms underlying cognitive decline.

The effect of blur on cortical responses to global form and motion

Global form and motion sensitivity undergo long development in childhood with motion sensitivity rather than form being impaired in a number of childhood disorders and both impaired in adult clinical populations. This suggests extended development and vulnerability of extrastriate cortical areas associated with global processing. However, in some developmental and clinical populations, it remains unclear to what extent impairments might reflect deficits at earlier stages of visual processing, such as reduced visual acuity and contrast sensitivity. To address this, we investigated the impact of degraded spatial vision on cortical global form and motion processing in healthy adults. Loss of high spatial frequencies was simulated using a diffuser to blur the stimuli. Participants completed behavioral and EEG tests of global form and motion perception under three levels of blur. For the behavioral tests, participants' form and motion coherence thresholds were measured using a two-alternative, forced-choice procedure. Steady-state visual evoked potentials were used to measure cortical responses to changes in the coherence of global form and motion stimuli. Both global form and global motion perception were impaired with increasing blur as measured by elevated behavioral thresholds and reduced cortical responses. However, form thresholds showed greater impairment in both behavioral and EEG measures than motion thresholds at the highest levels of blur. The results suggest that high spatial frequencies play an important role in the perception of both global form and motion but are especially significant for global form. Overall, the results reveal complex interactions between low-level factors and global visual processing, highlighting the importance of taking these factors into account when investigating extrastriate function in low vision populations.

Prenatal exposure to recreational drugs affects global motion perception in preschool children

Prenatal exposure to recreational drugs impairs motor and cognitive development; however it is currently unknown whether visual brain areas are affected. To address this question, we investigated the effect of prenatal drug exposure on global motion perception, a behavioural measure of processing within the dorsal extrastriate visual cortex that is thought to be particularly vulnerable to abnormal neurodevelopment. Global motion perception was measured in one hundred and forty-five 4.5-year-old children who had been exposed to different combinations of methamphetamine, alcohol, nicotine and marijuana prior to birth and 25 unexposed children. Self-reported drug use by the mothers was verified by meconium analysis. We found that global motion perception was impaired by prenatal exposure to alcohol and improved significantly by exposure to marijuana. Exposure to both drugs prenatally had no effect. Other visual functions such as habitual visual acuity and stereoacuity were not affected by drug exposure. Prenatal exposure to methamphetamine did not influence visual function. Our results demonstrate that prenatal drug exposure can influence a behavioural measure of visual development, but that the effects are dependent on the specific drugs used during pregnancy.

Global motion perception is independent from contrast sensitivity for coherent motion direction discrimination and visual acuity in 4.5-year-old children

Global motion processing depends on a network of brain regions that includes extrastriate area V5 in the dorsal visual stream. For this reason, psychophysical measures of global motion perception have been used to provide a behavioral measure of dorsal stream function. This approach assumes that global motion is relatively independent of visual functions that arise earlier in the visual processing hierarchy such as contrast sensitivity and visual acuity. We tested this assumption by assessing the relationships between global motion perception, contrast sensitivity for coherent motion direction discrimination (henceforth referred to as contrast sensitivity) and habitual visual acuity in a large group of 4.5-year-old children (n=117). The children were born at risk of abnormal neurodevelopment because of prenatal drug exposure or risk factors for neonatal hypoglycemia. Motion coherence thresholds, a measure of global motion perception, were assessed using random dot kinematograms. The contrast of the stimuli was fixed at 100% and coherence was varied. Contrast sensitivity was measured using the same stimuli by fixing motion coherence at 100% and varying dot contrast. Stereoacuity was also measured. Motion coherence thresholds were not correlated with contrast sensitivity or visual acuity. However, lower (better) motion coherence thresholds were correlated with finer stereoacuity (ρ=0.38, p=0.004). Contrast sensitivity and visual acuity were also correlated (ρ=-0.26, p=0.004) with each other. These results indicate that global motion perception for high contrast stimuli is independent of contrast sensitivity and visual acuity and can be used to assess motion integration mechanisms in children.

Motion perception: a review of developmental changes and the role of early visual experience

Significant controversies have arisen over the developmental trajectory for the perception of global motion. Studies diverge on the age at which it becomes adult-like, with estimates ranging from as young as 3 years to as old as 16. In this article, we review these apparently conflicting results and suggest a potentially unifying hypothesis that may also account for the contradictory literature in neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). We also discuss the extent to which patterned visual input during this period is necessary for the later development of motion perception. We conclude by addressing recent studies directly comparing different types of motion integration, both in typical and atypical development, and suggest areas ripe for future research.

Normative data for three tests of visuocognitive function in primary school children: cross-sectional study

Background/Aims

There is an increasing recognition that visuocognitive difficulties occur in children with neurodevelopmental problems. We obtained normative data for the performance of primary school children using three tests of visuocognitive function that are practicable in a clinical setting.

Methods

We tested 214 children aged between 4 and 11 years without known developmental problems, using tests to assess (1) orientation recognition and adaptive movement (postbox task), (2) object recognition (rectangles task) and (3) spatial integration (contours task).

Results

96% could do the postbox task with ease—only 4% (all aged <9 years) exhibited minor difficulties. Errors in the rectangles task decreased with age: 33% of children aged 4–5 years had major difficulties but >99% of children aged ≥6 years had no, or minor, difficulties. Median scores for the contours task improved with age, and after age 8 years, 99% could see the contour using long-range spatial integration rather than density.

Conclusions

These different aspects of children’s visuocognitive performance were testable in a field setting. The data provide a benchmark by which to judge performance of children with neurodevelopmental problems and may be useful in assessment with a view to providing effective supportive strategies for children whose visuocognitive skills are lower than the expectation for their age.