A specific deficit of dorsal stream function in Williams' syndrome

Manual action, fitting, and spatial planning: relating objects by young children

This study uses motion tracking technology to provide a new way of addressing the development of the ability to prospectively orient objects with respect to one another. A group of toddlers between 16 and 33 months of age (N=30) were studied in an object fitting task while they wore reflective markers on their hands to track spatial adjustments in three dimensions. Manual displacements of the handheld object were separated into translations and rotations. Results revealed that younger children largely used a two-step approach in which they initially translate an object to a target and subsequently attempt to rotate the object to match the target. In contrast, older children evidence more advanced spatial planning and integrate translational and rotational components throughout the entire period when they are transporting the object to the target. Additionally, at the oldest ages, children show even further improvements in coordinating translations and rotations by using relatively shorter translations (i.e., covering less distance) and by avoiding unnecessary rotations of the object. More broadly, the results offer insights into how manual problem solving becomes more efficient and planful during the toddler years.

Functional Reorganization of the Visual Dorsal Stream as Probed by 3-D Visual Coherence in Williams Syndrome

Object and depth perception from motion cues involves the recruitment of visual dorsal stream brain areas. In 3-D structure-from-motion (SFM) perception, motion and depth information are first extracted in this visual stream to allow object categorization, which is in turn mediated by the ventral visual stream. Such interplay justifies the use of SFM paradigms to understand dorsal–ventral integration of visual information. The nature of such processing is particularly interesting to be investigated in a neurological model of cognitive dissociation between dorsal (impaired) and ventral stream (relatively preserved) processing, Williams syndrome (WS). In the current fMRI study, we assessed dorsal versus ventral stream processing by using a performance-matched 3-D SFM object categorization task. We found evidence for substantial reorganization of the dorsal stream in WS as assessed by whole-brain ANOVA random effects analysis, with subtle differences in ventral activation. Dorsal reorganization was expressed by larger medial recruitment in WS (cuneus, precuneus, and retrosplenial cortex) in contrast with controls, which showed the expected dorsolateral pattern (caudal intraparietal sulcus and lateral occipital cortex). In summary, we found a substantial reorganization of dorsal stream regions in WS in response to simple visual categories and 3-D SFM perception, with less affected ventral stream. Our results corroborate the existence of a medial dorsal pathway that provides the substrate for information rerouting and reorganization in the presence of lateral dorsal stream vulnerability. This interpretation is consistent with recent findings suggesting parallel routing of information in medial and lateral parts of dorsal stream.

Perceiving and acting in depth in Williams syndrome and typical development

Individuals with the neurodevelopmental disorder Williams syndrome (WS) often report difficulty processing and acting in depth, such as crossing roads or reaching for objects; however little research attention has been directed at understanding depth perception and action in depth in WS and whether deficits in depth perception have an ocular or perceptual root in this group. This study assessed the extent and relationship of deficits in stereopsis (binocular, three dimensional vision) and actions performed in depth in WS, as well as in typically developing participants (TD) matched for non-verbal ability. Stereoacuity was age-appropriate in the TD group but at the level of a TD three year old in WS; one third of the WS group did not show evidence of stereopsis. When monocularly acting in depth there was no difference between the WS and TD groups. When binocularly acting in depth the WS group that did not exhibit stereopsis were significantly poorer than the TD group and the WS group that exhibited stereopsis. When assessing the relationship between stereoacuity and action in depth, stereoacuity negatively correlated with binocular action in depth for the WS group with stereopsis, but not the TD group. Therefore, no deficits in monocular depth perception in WS were evidenced, yet significant deficits are exhibited in binocular depth perception and action. Importantly action in depth under binocular viewing may be a useful gross screening measure for stereodeficits in WS. Remediation of depth perception deficits in WS could train further understanding of monocular cues to compensate for poor stereopsis.

Averaging, not internal noise, limits the development of coherent motion processing

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Motion processing abilities develop gradually through childhood.

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This lengthy development could be due to local noise and/or poor averaging.

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5–11-year-olds and adults performed equivalent noise and motion coherence tasks.

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Through childhood, internal noise reduces and averaging increases.

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Yet, only improved averaging explains developments in motion coherence sensitivity.

The development of motion processing is a critical part of visual development, allowing children to interact with moving objects and navigate within a dynamic environment. However, global motion processing, which requires pooling motion information across space, develops late, reaching adult-like levels only by mid-to-late childhood. The reasons underlying this protracted development are not yet fully understood. In this study, we sought to determine whether the development of motion coherence sensitivity is limited by internal noise (i.e., imprecision in estimating the directions of individual elements) and/or global pooling across local estimates. To this end, we presented equivalent noise direction discrimination tasks and motion coherence tasks at both slow (1.5°/s) and fast (6°/s) speeds to children aged 5, 7, 9 and 11 years, and adults. We show that, as children get older, their levels of internal noise reduce, and they are able to average across more local motion estimates. Regression analyses indicated, however, that age-related improvements in coherent motion perception are driven solely by improvements in averaging and not by reductions in internal noise. Our results suggest that the development of coherent motion sensitivity is primarily limited by developmental changes within brain regions involved in integrating motion signals (e.g., MT/V5).

Modality effect on contextual integration in people with Williams syndrome

In this study meaningful social stimuli were used as probes in a task requiring the judgment of semantic appropriateness to investigate contextual integration ability to test the ability of people with Williams syndrome (WS) to integrate information, as opposed to the use of meaningless syllables in audiovisual studies (the McGurk effect). Participants were presented with background auditory primes followed by targets that were either congruent or incongruent with the prime. Two modes of target were presented: a visual target (AV task) or an auditory target (AA task). Participants were asked to respond yes to contextually appropriate pairs and no to those that were contextually inappropriate. The congruency effect was measured as an index of successful central coherence. Similar to normally developing controls, people with WS showed shorter response latencies and greater accuracy in recognizing congruent pairs compared with incongruent pairs. Their performance did not differ from that of controls matched by mental age, but was inferior to that of controls matched by chronological age. The results revealed generalized contextual integration for auditory primes in both tasks, consistent with previous studies using visual presentation of social-related stimuli in people with WS (Hsu, 2013a, 2013c). Further demonstration of the presence of a modality effect on contextual coherence implies that cross-modal learning may be advantageous compared with unimodal learning.

Low vision due to cerebral visual impairment: differentiating between acquired and genetic causes

Background

To gain more insight into genetic causes of cerebral visual impairment (CVI) in children and to compare ophthalmological findings between genetic and acquired forms of CVI.

Methods

The clinical data of 309 individuals (mainly children) with CVI, and a visual acuity ≤0.3 were analyzed for etiology and ocular variables. A differentiation was made between acquired and genetic causes. However, in persons with West syndrome or hydrocephalus, it might be impossible to unravel whether CVI is caused by the seizure disorder or increased intracranial pressure or by the underlying disorder (that in itself can be acquired or genetic). In two subgroups, individuals with ‘purely’ acquired CVI and with ‘purely’ genetic CVI, the ocular variables (such as strabismus, pale optic disc and visual field defects) were compared.

Results

It was possible to identify a putative cause for CVI in 60% (184/309) of the cohort. In the remaining 40% the etiology could not be determined. A ‘purely’ acquired cause was identified in 80 of the patients (26%). West syndrome and/or hydrocephalus was identified in 21 patients (7%), and in 17 patients (6%) both an acquired cause and West and/or hydrocephalus was present. In 66 patients (21%) a genetic diagnosis was obtained, of which 38 (12%) had other possible risk factor (acquired, preterm birth, West syndrome or hydrocephalus), making differentiation between acquired and genetic not possible. In the remaining 28 patients (9%) a ‘purely’ genetic cause was identified.

CVI was identified for the first time in several genetic syndromes, such as ATR-X, Mowat-Wilson, and Pitt Hopkins syndrome. In the subgroup with ‘purely’ acquired causes (N = 80) strabismus (88% versus 64%), pale optic discs (65% versus 27%) and visual field defects (72% versus 30%) could be observed more frequent than in the subgroup with ‘purely’ genetic disorders (N = 28).

Conclusions

We conclude that CVI can be part of a genetic syndrome and that abnormal ocular findings are present more frequently in acquired forms of CVI.

Developmental changes in mental rotation ability and visual perspective-taking in children and adults with Williams syndrome

Williams syndrome (WS) is a genetic disorder caused by the partial deletion of chromosome 7. Individuals with WS have atypical cognitive abilities, such as hypersociability and compromised visuospatial cognition, although the mechanisms underlying these deficits, as well as the relationship between them, remain unclear. Here, we assessed performance in mental rotation (MR) and level 2 visual perspective taking (VPT2) tasks in individuals with and without WS. Individuals with WS obtained lower scores in the VPT2 task than in the MR task. These individuals also performed poorly on both the MR and VPT2 tasks compared with members of a control group. For the individuals in the control group, performance scores improved during development for both tasks, while the scores of those in the WS group improved only in the MR task, and not the VPT2 task. Therefore, we conducted a second experiment to explore the specific cognitive challenges faced by people with WS in the VPT2 task. In addition to asking participants to change their physical location (self-motion), we also asked them to adopt a third-person perspective by imagining that they had moved to a specified location (self-motion imagery). This enabled us to assess their ability to simulate the movement of their own bodies. The performance in the control group improved in both the self-motion and self-motion imagery tasks and both performances were correlated with verbal mental age. However, we did not find any developmental changes in performance for either task in the WS group. Performance scores for the self-motion imagery task in the WS group were low, similar to the scores observed for the VPT2 in this population. These results suggest that MR and VPT2 tasks involve different processes, and that these processes develop differently in people with WS. Moreover, difficulty completing VPT2 tasks may be partly because of an inability of people with WS to accurately simulate mental body motion.

Global motion perception in 2-year-old children: a method for psychophysical assessment and relationships with clinical measures of visual function

PURPOSE

We developed and validated a technique for measuring global motion perception in 2-year-old children, and assessed the relationship between global motion perception and other measures of visual function.

METHODS

Random dot kinematogram (RDK) stimuli were used to measure motion coherence thresholds in 366 children at risk of neurodevelopmental problems at 24 ± 1 months of age. RDKs of variable coherence were presented and eye movements were analyzed offline to grade the direction of the optokinetic reflex (OKR) for each trial. Motion coherence thresholds were calculated by fitting psychometric functions to the resulting datasets. Test-retest reliability was assessed in 15 children, and motion coherence thresholds were measured in a group of 10 adults using OKR and behavioral responses. Standard age-appropriate optometric tests also were performed.

RESULTS

Motion coherence thresholds were measured successfully in 336 (91.8%) children using the OKR technique, but only 31 (8.5%) using behavioral responses. The mean threshold was 41.7 ± 13.5% for 2-year-old children and 3.3 ± 1.2% for adults. Within-assessor reliability and test-retest reliability were high in children. Children's motion coherence thresholds were significantly correlated with stereoacuity (LANG I & II test, ρ = 0.29, P < 0.001; Frisby, ρ = 0.17, P = 0.022), but not with binocular visual acuity (ρ = 0.11, P = 0.07). In adults OKR and behavioral motion coherence thresholds were highly correlated (intraclass correlation = 0.81, P = 0.001).

CONCLUSIONS

Global motion perception can be measured in 2-year-old children using the OKR. This technique is reliable and data from adults suggest that motion coherence thresholds based on the OKR are related to motion perception. Global motion perception was related to stereoacuity in children.

Inferences about infants’ visual brain mechanisms

We discuss hypotheses that link the measurements we can make with infants to inferences about their developing neural mechanisms. First, we examine evidence from the sensitivity to visual stimulus properties seen in infants’ responses, using both electrophysiological measures (transient and steady-state recordings of visual evoked potentials/visual event-related potentials) and behavioral measures and compare this with the sensitivity of brain processes, known from data on mammalian neurophysiology and human neuroimaging. The evidence for multiple behavioral systems with different patterns of visual sensitivity is discussed. Second, we consider the analogies which can be made between infants’ behavior and that of adults with identified brain damage, and extend these links to hypothesize about the brain basis of visual deficits in infants and children with developmental disorders. Last, we consider how these lines of data might allow us to form “inverse linking hypotheses” about infants’ visual experience.

Visual control of manual actions: brain mechanisms in typical development and developmental disorders

Some key stages in the development of manual actions have been discussed in this supplement based on the idea of the dorsal cortical stream as the pathway for translating visual information into action control. We argue that visual information, transmitted through specialized visuomotor dorsal-stream modules, is required in the control of manual actions for selecting and attending to the target object of the action, translating visual spatial information into motor programmes and planning a coordinated sequence of actions so as to reach an optimal end-state. In typical development, we illustrate dorsal-stream processing through results on the use of stereoscopic information to guide infants' reaches, and changes in target selection and detailed kinematics of reaches depending on age, object size, and reaching in darkness (when dorsal-stream information rapidly decays). We hypothesize 'dorsal-stream vulnerability' as a widespread feature of neurodevelopmental disorders, such as autism, Williams syndrome, and children born very preterm. Such deficits, identified as abnormal visuomanual actions, are seen in bimanual coordination, visual guidance of action in the 'postbox' task, and failures in motor planning for end-state comfort. We discuss the possible application of these approaches to a wider range of disorders including developmental coordination disorder.

Space and language in Williams syndrome: insights from typical development

One of the holy grails of cognitive science is to understand the causal chain that links genes and cognition. Genetic syndromes accompanied by cognitive effects offer natural experiments that can uniquely inform our understanding of this chain. In this article, we discuss the case of Williams syndrome (WS), which is characterized by a set of missing genes on chromosome 7q11.23, and presents with a unique cognitive profile that includes severe spatial impairment along with strikingly fluent and well-structured language. An early inference from this profile was the idea that a small group of genes could directly target one cognitive system while leaving others unaffected. Recent evidence shows that this inference fails. First, the profile within the spatial domain is varied, with relative strength in some aspects of spatial representation but severe impairment in others. Second, some aspects of language may fail to develop fully, raising the question of how to compare the resilience and fragility of the two key cognitive domains in this syndrome. Third, much research on the profile fails to place findings in the context of typical developmental trajectories. We explore these points and propose a new hypothesis that explains the unusual WS cognitive profile by considering normal mechanisms of cognitive development that undergo change on an extremely prolonged timetable. This hypothesis places the elements of the WS cognitive profile in a new light, refocuses the discussion of the gene-cognition causal chain for WS and other disorders, and more generally, underlines the importance of understanding cognitive structure in both typical and atypical development. WIREs Cogn Sci 2013, 4:693-703. doi: 10.1002/wcs.1258 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Global dot integration in typically developing children and in Williams syndrome

Williams Syndrome (WS) is a neurodevelopmental disorder that results in deficits in visuospatial perception and cognition. The dorsal stream vulnerability hypothesis in WS predicts that visual motion processes are more susceptible to damage than visual form processes. We asked WS participants and typically developing children to detect the global structure Glass patterns, under "static" and "dynamic" conditions in order to evaluate this hypothesis. Sequentially presented Glass patterns are coined as dynamic because they induce illusory motion, which is modeled after the interaction between orientation (form) and direction (motion) mechanisms. If the dorsal stream vulnerability holds in WS participants, then they should process real and illusory motion atypically. However, results are consistent with the idea that form and motion integration mechanisms are functionally delayed or attenuated in WS. Form coherence thresholds for both static and dynamic Glass patterns in WS were similar to those of 4-5year old children, younger than what is predicted by mental age. Dynamic presentation of Glass patterns improved thresholds to the same degree as typical participants. Motion coherence thresholds in WS were similar to those of mental age matches. These data pose constraints on the dorsal vulnerability hypothesis, and refine our understanding of the relationship between form and motion processing in development.

Looking around houses: attention to a model when drawing complex shapes in Williams syndrome and typical development

Drawings by individuals with Williams syndrome (WS) typically lack cohesion. The popular hypothesis is that this is a result of excessive focus on local-level detail at the expense of global configuration. In this study, we explored a novel hypothesis that inadequate attention might underpin drawing in WS. WS and typically developing (TD) non-verbal ability matched groups copied and traced a house figure comprised of geometric shapes. The house was presented on a computer screen for 5-s periods and participants pressed a key to re-view the model. Frequency of key-presses indexed the looks to the model. The order that elements were replicated was recorded to assess hierarchisation of elements. If a lack of attention to the model explained poor drawing performance, we expected participants with WS to look less frequently to the model than TD children when copying. If a local-processing preference underpins drawing in WS, more local than global elements would be produced. Results supported the first, but not second hypothesis. The WS group looked to the model infrequently, but global, not local, parts were drawn first, scaffolding local-level details. Both groups adopted a similar order of drawing and tracing of parts, suggesting typical, although delayed strategy-use in the WS group. Additionally both groups drew larger elements of the model before smaller elements, suggested a size-bias when drawing.

Processing slow and fast motion in children with autism spectrum conditions

Consistent with the dorsal stream hypothesis, difficulties processing dynamic information have previously been reported in individuals with autism spectrum conditions (ASC). However, no research has systematically compared motion processing abilities for slow and fast speeds. Here, we measured speed discrimination thresholds and motion coherence thresholds in slow (1.5 deg/sec) and fast (6 deg/sec) speed conditions in children with an ASC aged 7 to 14 years, and age- and ability-matched typically developing children. Unexpectedly, children with ASC were as sensitive as typically developing children to differences in speed at both slow and fast reference speeds. Yet, elevated motion coherence thresholds were found in children with ASC, but in the slow stimulus speed condition only. Rather than having pervasive difficulties in motion processing, as predicted by the dorsal stream hypothesis, these results suggest that children with ASC have a selective difficulty in extracting coherent motion information specifically at slow speeds. Understanding the effects of stimulus parameters such as stimulus speed will be important for resolving discrepancies between previous studies examining motion coherence thresholds in ASC and also for refining theoretical models of altered autistic perception.

Abnormal visual motion processing is not a cause of dyslexia

Developmental dyslexia is a reading disorder, yet deficits also manifest in the magnocellular-dominated dorsal visual system. Uncertainty about whether visual deficits are causal or consequential to reading disability encumbers accurate identification and appropriate treatment of this common learning disability. Using fMRI, we demonstrate in typical readers a relationship between reading ability and activity in area V5/MT during visual motion processing and, as expected, also found lower V5/MT activity for dyslexic children compared to age-matched controls. However, when dyslexics were matched to younger controls on reading ability, no differences emerged, suggesting that weakness in V5/MT may not be causal to dyslexia. To further test for causality, dyslexics underwent a phonological-based reading intervention. Surprisingly, V5/MT activity increased along with intervention-driven reading gains, demonstrating that activity here is mobilized through reading. Our results provide strong evidence that visual magnocellular dysfunction is not causal to dyslexia but may instead be consequential to impoverished reading.

VIDEO ABSTRACT

Electrophysiological study of face inversion effects in Williams syndrome

OBJECTIVE

In order to evaluate whether face perception is intact or not in Williams syndrome (WS), the face inversion effects (FIE) in the event-related potential (ERP) or magnetoencephalography (MEG) were investigated in three teenaged patients with WS.

METHODS

Responses to the inverted faces and upright faces were compared using MEG for one 13year old girl with WS (subject A) and ERP for boys with WS at 16 and 14years of age (subjects B and C, respectively).

RESULTS

Although age-matched control children showed FIE in both MEG and ERP studies, two subjects (A and B) with WS showed no FIE at all. The neurophysiological data of ERP in subject B was significantly different from those of the age-matched controls. On the other hand, a boy with WS (subject C) showed typical FIE in the same manner as the age-matched controls.

CONCLUSIONS

The difference between those with or without FIE was not explained merely by the chronological age, a simple delay in mental age or in the ability to discriminate among upright faces. The absence of FIE may be related to the severity of a deficit in the dorsal pathway function that is characteristic to the syndrome.

Do different 'magnocellular tasks' probe the same neural substrate?

The sensory abnormalities associated with disorders such as dyslexia, autism and schizophrenia have often been attributed to a generalized deficit in the visual magnocellular-dorsal stream and its auditory homologue. To probe magnocellular function, various psychophysical tasks are often employed that require the processing of rapidly changing stimuli. But is performance on these several tasks supported by a common substrate? To answer this question, we tested a cohort of 1060 individuals on four 'magnocellular tasks': detection of low-spatial-frequency gratings reversing in contrast at a high temporal frequency (so-called frequency-doubled gratings); detection of pulsed low-spatial-frequency gratings on a steady luminance pedestal; detection of coherent motion; and auditory discrimination of temporal order. Although all tasks showed test-retest reliability, only one pair shared more than 4 per cent of variance. Correlations within the set of 'magnocellular tasks' were similar to the correlations between those tasks and a 'non-magnocellular task', and there was little consistency between 'magnocellular deficit' groups comprising individuals with the lowest sensitivity for each task. Our results suggest that different 'magnocellular tasks' reflect different sources of variance, and thus are not general measures of 'magnocellular function'.

Motion perception in children with foetal alcohol syndrome

AIM

To evaluate the visual magnocellular pathway by a coherent motion perception test in children with foetal alcohol syndrome (FAS).

METHODS

Eighty-nine children (49 with verified FAS and 40 without FAS) aged from 10 to 16 years were included into the study. Both the study and the control group were children living in orphanages. A coherent motion perception test was used. The test consisted of 150 white moving dots on a black background presented in different signal-to-noise ratio conditions. The task was direction detection of the coherently moving dots whose percentage decreased at each step.

RESULTS

A significant difference between the two groups was found (p = 0.018). Children with FAS had lower coherent motion perception ability in all the signal-to-noise ratio conditions. A significant difference between difficulty levels (p < 0.001) was found for all subjects in both groups - decreasing the stimulus signal-to-noise level decreased the motion perception score. In both groups, the motion perception score differed for vertical and horizontal stimuli (p = 0.003) with better performance with vertical stimuli.

CONCLUSION

Impaired motion perception in FAS children could be indicative of a dorsal stream developmental dysfunction resulting from alcohol brain damage.

Visually guided step descent in children with Williams syndrome

Individuals with Williams syndrome (WS) have impairments in visuospatial tasks and in manual visuomotor control, consistent with parietal and cerebellar abnormalities. Here we examined whether individuals with WS also have difficulties in visually controlling whole-body movements. We investigated visual control of stepping down at a change of level in children with WS (5-16-year-olds), who descended a single step while their movement was kinematically recorded. On each trial step height was set unpredictably, so that visual information was necessary to perceive the step depth and position the legs appropriately before landing. Kinematic measures established that children with WS did not use visual information to slow the leg at an appropriate point during the step. This pattern contrasts with that observed in typically developing 3- and 4-year-old children, implying severe impairment in whole-body visuomotor control in WS. For children with WS, performance was not significantly predicted by low-level visual or balance problems, but improved significantly with verbal age. The results suggest some plasticity and development in WS whole-body control. These data clearly show that visuospatial and visuomotor deficits in WS extend to the locomotor domain. Taken together with evidence for parietal and cerebellar abnormalities in WS, these results also provide new evidence for the role of these circuits in the visual control of whole-body movement.

Vision for action in toddlers: the posting task

Three experiments examine 18- to 24-month-old (N = 78) toddlers' ability to spatially orient objects by their major axes for insertion into a slot. This is a simplified version of the posting task that is commonly used to measure dorsal stream functioning. The experiments identify marked developmental changes in children's ability to preorient objects for insertion, with 18-month-olds failing completely and 24-month-olds succeeding easily. In marked contrast, 18-month-olds preorient their empty hands for insertion into the same slots. This developmental dissociation between aligning hands and aligning objects to slots suggests that the key developmental change is in action with the goal of object-to-object alignment versus action on an object.

Gait adaptation during obstacle crossing reveals impairments in the visual control of locomotion in Williams syndrome

Recent evidence indicates that individuals with Williams syndrome (WS), a rare genetically based neurodevelopmental disorder, show abnormalities of parietal and cerebellar regions of the brain that may be involved in the visual control of locomotion. Here we examined whether parietal and cerebellar abnormalities contribute to deficits in spatiotemporal characteristics and foot placement variability during obstacle crossing in adults with WS, when compared with an IQ-matched group of adults with Down syndrome (DS) and typically developing adult controls. We used the GAITRite walkway to examine the spatiotemporal characteristics and foot placement variability relative to a small ground-based obstacle in the travel path. We found that adults with WS showed late adjustments to spatiotemporal gait characteristics alongside an exaggerated and more spatially constrained visual guidance of foot positioning in the final steps prior to stepping over the obstacle. In contrast, the adults with DS showed longer step duration and more variable step length and step duration during the crossing and recovery steps after the obstacle, suggestive of cerebellar dysfunction. Although the controls were able to reduce the variability of foot placement across the obstacle crossing trials, both the WS and DS groups did not become more consistent with practice. These findings indicate a less flexible and overly constrained visuomotor system in WS, which is consistent with more widespread and diffuse abnormalities in parietal and cerebellar regions.

Visual processing in Noonan syndrome: dorsal and ventral stream sensitivity

Global spatial and motion processing abilities were assessed in 18 patients with Noonan syndrome (NS) and in 43 matched controls using form and motion coherence testing, respectively. We observed a discrepancy between the two groups since the study group had significantly lower performances than the control group for form coherence while there was no impairment on motion coherence. All the patients were also assessed on the Movement Assessment Battery for Children (M-ABC) to evaluate visuomotor skills. Thirteen of the 18 (72%) also had global poor performances on the M-ABC. The results show that children with NS have a specific impairment in the global processing of visuospatial information and are likely to have a specific ventral stream deficit as also suggested by the frequent visuomotor perceptual difficulties. Testing form and motion coherence thresholds may be a useful diagnostic tool for this group of patients, despite their normal cognitive abilities, since aspects of global form processing and visuomotor perceptual difficulties can be identified and potentially targeted for a specific rehabilitation program.

No evidence for a fundamental visual motion processing deficit in adolescents with autism spectrum disorders

It has been suggested that atypicalities in low-level visual processing contribute to the expression and development of the unusual cognitive and behavioral profile seen in autism spectrum disorders (ASD). However, previous investigations have yielded mixed results. In the largest study of its kind (ASD n = 89; non-ASD = 52; mean age 15 years 6 months) and testing across the spectrum of IQ (range 52-133), we investigated performance on three measures of basic visual processing: motion coherence, form-from-motion and biological motion (BM). At the group level, we found no evidence of differences between the two groups on any of the tasks, suggesting that there is no fundamental visual motion processing deficit in individuals with an ASD, at least by adolescence. However, we identified a tail of individuals with ASD (18% of the sample) who had exceptionally poor BM processing abilities compared to the non-ASD group, and who were characterized by low IQ. For the entire sample of those both with and without ASD, performance on the BM task uniquely correlated with performance on the Frith-Happé animations, a higher-level task that demands the interpretation of moving, interacting agents in order to understand mental states. We hypothesize that this association reflects the shared social-cognitive characteristics of the two tasks, which have a common neural underpinning in the superior temporal sulcus.

Time crawls: the temporal resolution of infants' visual attention

Conscious visual perception of the constantly changing environment is one of the brain's most critical functions. In virtually every moment of every daily activity, the visual system is confronted with the task of accurately representing and interpreting scenes that change rapidly over time. Adults can judge the identity and order of changing images presented at a rate of up to 10 Hz (~50 ms per image); this limit reflects a finite temporal resolution of attention. In the research reported here, although 6- to 15-month-old infants could detect the presence of rapid flicker without difficulty, their ability to segment individual alternating states within the flicker was severely limited: Fifteen-month-old infants had a temporal resolution of attention approximately one order of magnitude lower than that of adults (~1 Hz). Coarse temporal resolution constrains how infants perceive and utilize dynamic visual information and may play a role in the visual processing deficits found in individuals with neurodevelopmental disorders.

Development of human visual function

By 1985 newly devised behavioral and electrophysiological techniques had been used to track development of infants' acuity, contrast sensitivity and binocularity, and for clinical evaluation of developing visual function. This review focus on advances in the development and assessment of infant vision in the following 25 years. Infants' visual cortical function has been studied through selectivity for orientation, directional motion and binocular disparity, and the control of subcortical oculomotor mechanisms in fixation shifts and optokinetic nystagmus, leading to a model of increasing cortical dominance over subcortical pathways. Neonatal face processing remains a challenge for this model. Recent research has focused on development of integrative processing (hyperacuity, texture segmentation, and sensitivity to global form and motion coherence) in extra-striate visual areas, including signatures of dorsal and ventral stream processing. Asynchronies in development of these two streams may be related to their differential vulnerability in both acquired and genetic disorders. New methods and approaches to clinical disorders are reviewed, in particular the increasing focus on paediatric neurology as well as ophthalmology. Visual measures in early infancy in high-risk children are allowing measures not only of existing deficits in infancy but prediction of later visual and cognitive outcome. Work with early cataract and later recovery from blinding disorders has thrown new light on the plasticity of the visual system and its limitations. The review concludes with a forward look to future opportunities provided by studies of development post infancy, new imaging and eye tracking methods, and sampling infants' visual ecology.

Fragile X protein expression is linked to visual functions in healthy male volunteers

Fragile X syndrome (FXS) is characterized by the impairment of the magnocellular/dorsal visual system. In this study, we explored how fragile X protein (FMRP) expression may affect visual functions in healthy participants. The percentage of FMRP-positive lymphocytes was measured using a rapid antibody test in blood smears of 100 male volunteers. CGG triplet expansion was also determined. Results revealed that participants with fewer FMRP-positive lymphocytes exhibited lower performances on tests biasing information processing toward the magnocellular pathway and dorsal visual stream (contrast sensitivity at low spatial/high temporal frequency and motion coherence). It was not observed in the case of tests biasing information processing toward the parvocellular pathway and ventral stream (contrast sensitivity at high spatial/low temporal frequency and form coherence). These results suggest that healthy persons with lower peripheral FMRP expression display a visual phenotype similar to that described in patients with FXS.

Visual perception in preterm children: what are we currently measuring?

Over the past two decades, cerebral visual impairment has been recognized as a principal deficit in preterm children, and in particular those with cerebral palsy. We review the current knowledge of visual processing deficits in these children, and provide an overview of the tools for assessing cerebral visual impairment. Commercially available instruments are usually directed at evaluating visuospatial skills rather than detecting object recognition difficulties. Particularly in children aged 3 years or younger and in children with multiple handicaps, cerebral visual impairment is difficult to diagnose. This difficulty may be attributable to limitations specific to the instrument, such as a test that is inappropriate for age, or to child-specific limitations such as motor impairment or speech delay. We therefore include an overview of relevant neuroimaging findings reported in these children, focusing on the most recent imaging modalities. Novel techniques such as diffusion tensor imaging may provide sensitive markers of cerebral visual impairment in situations where clinical diagnosis is difficult, and such approaches may allow for early intervention.

Severity of hyperacusis predicts individual differences in speech perception in Williams Syndrome

BACKGROUND

Williams Syndrome (WS) is a neurodevelopmental disorder of genetic origin, characterised by relative proficiency in language in the face of serious impairment in several other domains. Individuals with WS display an unusual sensitivity to noise, known as hyperacusis.

METHODS

In this study, we examined the extent to which hyperacusis interferes with the perception of speech in children and adults with WS. Participants were required to discriminate words which differed in one consonant of a cluster when these contrasts were embedded in a background of noise.

RESULTS

Although the introduction of noise interfered with performance on a consonant cluster discrimination task equally in the WS and control groups, the severity of hyperacusis significantly predicted individual variability in speech perception within the WS group.

CONCLUSIONS

These results suggest that alterations in sensitivity to input mediate atypical pathways for language development in WS, where hyperacusis exerts an important influence together with other non-auditory factors.

Patterns and trajectories in Williams Syndrome: the case of visual orientation discrimination

Williams Syndrome (WS) is a developmental disorder typified by deficits in visuospatial cognition. To understand the nature of this deficit, we characterized how people with WS perceive visual orientation, a fundamental ability related to object identification. We compared WS participants to typically developing children (3-6 years of age) and typical adults in an orientation discrimination task with four stimulus types (small circular, large circular, collinear elongated and parallel elongated gratings). We measured orientation discrimination thresholds and the proportion of orthogonal errors (i.e., mirror-image reversal errors). We evaluated how these metrics (1) are modulated by stimulus condition, and (2) vary with chronological or mental age. We found that orientation perception in WS is comparable to that of typically developing children. Orientation discrimination thresholds were better for elongated gratings than circular gratings across all participant groups. For large circular gratings, the proportion of orthogonal errors was disproportionately greater in WS participants and typically developing 3-6 year old children than in typical adults. Moreover, we found that the ability to judge orientation in WS improves with increasing mental age, but not chronological age. These results suggest that orientation discrimination in WS is developmentally arrested, as opposed to abnormal or delayed.

Object recognition in Williams syndrome: uneven ventral stream activation

Williams syndrome (WS) is a genetic disorder associated with severe visuospatial deficits, relatively strong language skills, heightened social interest, and increased attention to faces. On the basis of the visuospatial deficits, this disorder has been characterized primarily as a deficit of the dorsal stream, the occipitoparietal brain regions that subserve visuospatial processing. However, some evidence indicates that this disorder may also affect the development of the ventral stream, the occipitotemporal cortical regions that subserve face and object recognition. The present studies examined ventral stream function in WS, with the hypothesis that faces would produce a relatively more mature pattern of ventral occipitotemporal activation, relative to other objects that are also represented across these visual areas. Using functional magnetic imaging, we compared activation patterns during viewing of human faces, cat faces, houses and shoes in individuals with WS (age 14-27), typically developing 6-9-year-olds (matched approximately on mental age), and typically developing 14-26-year-olds (matched on chronological age). Typically developing individuals exhibited changes in the pattern of activation over age, consistent with previous reports. The ventral stream topography of individuals with WS differed from both control groups, however, reflecting the same level of activation to face stimuli as chronological age matches, but less activation to house stimuli than either mental age or chronological age matches. We discuss the possible causes of this unusual topography and implications for understanding the behavioral profile of people with WS.

Visual perceptual difficulties and under-achievement at school in a large community-based sample of children

INTRODUCTION

Difficulties with visual perception (VP) are often described in children with neurological or developmental problems. However, there are few data regarding the range of visual perceptual abilities in populations of normal children, or on the impact of these abilities on children's day-to-day functioning.

METHODS

Data were obtained for 4512 participants in an ongoing birth cohort study (Avon Longitudinal Study of Parents and Children; ALSPAC). The children's mothers responded to questions designed to elicit indications of visual perceptual difficulties or immaturity, when their children were aged 13 years. We examined associations with standardised school test results in reading and in mathematics at age 13-14 years (SATS-KS3), accounting for potential confounders including IQ.

RESULTS

Three underlying factors explained half the variance in the VP question responses. These correlated best with questions on interpreting cluttered scenes; guidance of movement and face recognition. The adjusted parameter estimates (95% CI) for the cluttered-scenes factor (0.05; 0.02 to 0.08; p<0.001) suggested positive associations with the reading test results whilst that for the guidance-of-movement factor (0.03; 0.00 to 0.06; p = 0.026) suggested positive association with the mathematics results. The raw scores were associated with both test results.

DISCUSSION

VP abilities were widely distributed in this sample of 13-year old children. Lower levels of VP function were associated with under-achievement in reading and in mathematics. Simple interventions can help children with VP difficulties, so research is needed into practicable, cost-effective strategies for identification and assessment, so that support can be targeted appropriately.

Using perceptual signatures to define and dissociate condition-specific neural etiology: autism and fragile X syndrome as model conditions

The functional link between genetic alteration and behavioral end-state is rarely straightforward and never linear. Cases where neurodevelopmental conditions defined by a distinct genetic etiology share behavioral phenotypes are exemplary, as is the case for autism and Fragile X Syndrome (FXS). In this paper and its companion paper, we propose a method for assessing the functional link between genotype and neural alteration across these target conditions by comparing their perceptual signatures. In the present paper, we discuss how such signatures can be used to (1) define and differentiate various aspects of neural functioning in autism and FXS, and subsequently, (2) to infer candidate causal (genetic) mechanisms based on such signatures (see companion paper, this issue).

From genes to brain development to phenotypic behavior: "dorsal-stream vulnerability" in relation to spatial cognition, attention, and planning of actions in Williams syndrome (WS) and other developmental disorders

Visual information is believed to be processed through two distinct, yet interacting cortical streams. The ventral stream performs the computations needed for recognition of objects and faces ("what" and "who"?) and the dorsal stream the computations for registering spatial relationships and for controlling visually guided actions ("where" and "how"?). We initially proposed a model of spatial deficits in Williams syndrome (WS) in which visual abilities subserved by the ventral stream, such as face recognition, are relatively well developed (although not necessarily in exactly the same way as in typical development), whereas dorsal-stream functions, such as visuospatial actions, are markedly impaired. Since these initial findings in WS, deficits of motion coherence sensitivity, a dorsal-stream function has been found in other genetic disorders such as Fragile X and autism, and as a consequence of perinatal events (in hemiplegia, perinatal brain anomalies following very premature birth), leading to the proposal of a general "dorsal-stream vulnerability" in many different conditions of abnormal human development. In addition, dorsal-stream systems provide information used in tasks of visuospatial memory and locomotor planning, and these systems are closely coupled to networks for attentional control. We and several other research groups have previously shown deficits of frontal and parietal lobe function in WS individuals for specific attention tasks [e.g., Atkinson, J., Braddick, O., Anker, S., Curran, W., & Andrew, R. (2003). Neurobiological models of visuospatial cognition in children with Williams Syndrome: Measures of dorsal-stream and frontal function. Developmental Neuropsychology, 23(1/2), 141-174.]. We have used the Test of Everyday Attention for Children (TEA-Ch) which aims to attempt to separate components of attention with distinct brain networks (selective attention, sustained attention, and attention control-executive function) testing a group of older children with WS, but this test battery is too demanding for many children and adults with WS. Consequently, we have devised a new set of tests of attention, the Early Childhood Attention Battery (ECAB). This uses similar principles to the TEA-Ch, but adapted for mental ages younger than 6 years. The ECAB shows a distinctive attention profile for WS individuals relative to their overall cognitive development, with relative strength in tasks of sustained attention and poorer performance on tasks of selective attention and executive control. These profiles, and the characteristic developmental courses, also show differences between children with Down's syndrome and WS. This chapter briefly reviews new research findings on WS in these areas, relating the development of brain systems in WS to evidence from neuroimaging in typically developing infants, children born very preterm, and normal adults. The hypothesis of "dorsal-stream(s) vulnerability" which will be discussed includes a number of interlinked brain networks, subserving not only global visual processing and formulation of visuomotor actions but interlinked networks of attention.

A kinematic analysis of visually-guided movement in Williams syndrome

Previous studies have reported that people with the neurodevelopmental disorder Williams syndrome exhibit difficulties with visuomotor control. In the current study, we examined the extent to which visuomotor deficits were associated with movement planning or feedback-based on-line control. We used a variant of the Fitts' reciprocal aiming task on a computerized touchscreen in adults with WS, IQ-matched individuals with Down syndrome (DS), and typically developing controls. By manipulating task difficulty both as a function of target size and amplitude, we were able to vary the requirements for accuracy to examine processes associated with dorsal visual stream and cerebellar functioning. Although a greater increase in movement time as a function of task difficulty was observed in the two clinical groups with WS and DS, greater magnitude in the late kinematic components of movement-specifically, time after peak velocity-was revealed in the WS group during increased demands for accuracy. In contrast, the DS group showed a greater speed-accuracy trade-off with significantly reduced and more variable endpoint accuracy, which may be associated with cerebellar deficits. In addition, the WS group spent more time stationary in the target when task-related features reflected a higher level of difficulty, suggestive of specific deficits in movement planning. Our results indicate that the visuomotor coordination deficits in WS may reflect known impairments of the dorsal stream, but may also indicate a role for the cerebellum in dynamic feed-forward motor control.

Coherence motion perception in developmental dyslexia: a meta-analysis of behavioral studies

The magnitude of the association between developmental dyslexia (DD) and motion sensitivity is evaluated in 35 studies, which investigated coherence motion perception in DD. A first analysis is conducted on the differences between DD groups and age-matched control (C) groups. In a second analysis, the relationship between motion coherence threshold and reading ability is considered. Globally, the mean effect size (ES) is moderate (d = 0.675, 2334 subjects) with a large value (d = 0.747) for the between-groups differences in motion perception and a smaller mean ES (d = 0.178) for the correlational studies. The influence on ES of the stimuli parameters and subjects age is analyzed. The number of dots, the age of the subjects, and the type of analysis (i.e. between-group or correlational) are significantly related to the ES. Looking at the ES values, a smaller number of dots constituting the stimuli are associated with larger ES and, interestingly, the children studies are associated with lower ES in comparison with the researches evaluating adults. The large ES value supports the importance of studying motion perception deficits in DD groups, consistently with the claim that dorsal impairment/noise-exclusion deficit could be one of the risk factor of reading difficulties.

Electrophysiological study of local/global processing in Williams syndrome

Persons with Williams syndrome (WS) demonstrate pronounced deficits in visuo-spatial processing. The purpose of the current study was to examine the preferred level of perceptual analysis in young adults with WS (n = 21) and the role of attention in the processing of hierarchical stimuli. Navon-like letter stimuli were presented to adults with WS and age-matched typical controls in an oddball paradigm where local and global targets could appear with equal probability. Participants received no explicit instruction to direct their attention toward a particular stimulus level. Behavioral and event-related potential (ERP) data were recorded. Behavioral data indicated presence of a global precedence effect in persons with WS. However, their ERP responses revealed atypical brain mechanisms underlying attention to local information. During the early perceptual analysis, global targets resulted in reduced P1 and enhanced N150 responses in both participant groups. However, only the typical comparison group demonstrated a larger N150 to local targets. At the more advanced stages of cognitive processing, a larger P3b response to global and local targets was observed in the typical group but not in persons with WS, who instead demonstrated an enhanced P3a to global targets only. The results indicate that in a perceptual task, adults with WS may experience greater than typical global-to-local interference and not allocate sufficient attentional resources to local information.

Developmental profiles for multiple object tracking and spatial memory: typically developing preschoolers and people with Williams syndrome

The ability to track moving objects, a crucial skill for mature performance on everyday spatial tasks, has been hypothesized to require a specialized mechanism that may be available in infancy (i.e. indexes). Consistent with the idea of specialization, our previous work showed that object tracking was more impaired than a matched spatial memory task in individuals with Williams syndrome (WS), a genetic disorder characterized by severe visuo-spatial impairment. We now ask whether this unusual pattern of performance is a reflection of general immaturity or of true abnormality, possibly reflecting the atypical brain development in WS. To examine these two possibilities, we tested typically developing 3- and 4-year-olds and people with WS on multiple object tracking (MOT) and memory for static spatial location. The maximum number of objects that could be correctly tracked or remembered (estimated from the k-statistic) showed similar developmental profiles in typically developing 3- and 4-year-old children, but the WS profile differed from either age group. People with WS could track more objects than 3-year-olds, and the same number as 4-year-olds, but they could remember the locations of more static objects than both 3- and 4-year-olds. Combining these data with those from our previous studies, we found that typically developing children show increases in the number of objects they can track or remember between the ages of 3 and 6, and these increases grow in parallel across the two tasks. In contrast, object tracking in older children and adults with WS remains at the level of 4-year-olds, whereas the ability to remember multiple locations of static objects develops further. As a whole, the evidence suggests that MOT and memory for static location develop in tandem typically, but not in WS. Atypical development of the parietal lobe in people with WS could play a causal role in the abnormal, uneven pattern of performance in WS. This interpretation is consistent with the idea that multiple object tracking engages different mechanisms from those involved in memory for static object location, and that the former can be particularly disrupted by atypical development.

Executive functions in individuals with Williams syndrome

BACKGROUND

The present study was aimed at investigating working memory (WM) and executive functions capacities in individuals with Williams syndrome (WS) as compared with mental-age matched typically developing (TD) children.

METHOD

In order to serve the study goal, a sizeable battery of tasks tapping WM as well as attention, memory, planning, categorisation, shifting and inhibition abilities was administered to 15 individuals with WS (mean chronological age of 19.11 and mean mental age of 6.10), and to a group of 15 TD children (mean chronological age of 7.6 and mean mental age of 6.9).

RESULTS

Participants with WS showed deficits in both verbal and visual-spatial modalities for selective and sustained attention, short-term memory and WM, planning and inhibition. However, considering categorisation and shifting abilities, relatively unimpaired performance emerged on those tasks relying on verbal materials.

CONCLUSIONS

These findings are both relevant to improve our knowledge about certain qualitative aspects of the anomalous cognitive development in WS as well as for its eventual clinical implications.

Vision in developmental disorders: is there a dorsal stream deficit?

The main aim of this review is to evaluate the proposal that several developmental disorders affecting vision share an impairment of the dorsal visual stream. First, the current definitions and common measurement approaches used to assess differences in both local and global functioning within the visual system are considered. Next, studies assessing local and global processing in the dorsal and ventral visual pathways are reviewed for five developmental conditions for which early to mid level visual abilities have been assessed: developmental dyslexia, autism spectrum disorders, developmental dyspraxia, Williams syndrome and Fragile X syndrome. The reviewed evidence is broadly consistent with the idea that the dorsal visual stream is affected in developmental disorders. However, the potential for a unique profile of visual abilities that distinguish some of the conditions is posited, given that for some of these disorders ventral stream deficits have also been found. We conclude with ideas regarding future directions for the study of visual perception in children with developmental disorders using psychophysical measures.

Reorganization of global form and motion processing during human visual development

The functional selectivity of human primary visual cortex (V1) for orientation and motion direction is established by around 3 months of age [1-3], but there have been few studies of the development of extrastriate visual areas that integrate outputs from V1 [4-8]. We investigated sensitivity and topographical organization for global form and motion with high-density visual event-related potentials (VERPs) in 4- to 5-month-old infants and adults. Responses were measured to transitions between concentrically organized elements (short arc segments for form, dot trajectories for motion) and random arrangements. Adults showed topographically separate responses, with midline motion and more lateral form responses. Of 26 infants, 25 showed significant motion responses but only 13 showed form responses, suggesting more advanced development for extrastriate motion areas than form. Infants' form and motion responses were topographically distinct but contrasted with the corresponding adult topographies, with infants' motion responses more lateral than form responses. These results imply distinct neural sources at both ages and raise the possibility of substantial reorganization of extrastriate networks between infancy and adulthood. We speculate that global motion responses arise from area V5 in infants but are dominated by more medial areas such as V3/V3A and V6 in adults.

Effects of external and internal cues on gait function in Williams syndrome

Williams syndrome (WS), a rare genetically based neurodevelopmental disorder, is characterized by gait abnormalities that resemble basal ganglia-parkinsonian deficits in the internal regulation of stride length. In the current study, we explored whether visual or attentional cues would improve gait function in adults with WS, when compared to adults with Down syndrome (DS) and neurologically normal controls. The spatiotemporal characteristics of gait were measured using the GAITRite walkway while participants walked with visual cues set at 20% greater than preferred stride length (externally cued), or with an attentional strategy of maintaining the stride length without the assistance of visual cues (internally cued). Although the WS and DS groups were able to achieve the criterion and normalize stride length in both conditions, the WS group significantly reduced their gait speed and cadence in the externally cued condition when compared to controls. In the internally cued condition, the WS group also showed reduced speed and increased intra-individual variability in speed and stride time. These findings suggest that the primary deficit is not one of difficulty regulating stride length in WS, but rather indicates more widespread dysfunction within visuomotor regions.