Visual and visuospatial development in young children with Williams syndrome

Emotions in action through the looking glass

The paper aims at highlighting how our primary understanding of others' actions is rooted in the mirror mechanism. To this end, the anatomical architecture of the mirror neuron system for action will be outlined as well as its role in grasping goals and intentions in others' motor behaviour. One further step through the looking glass of social cognition will be referring to the ubiquitous emotional colouring of actions and considering its links with the motor domain. This will allow a clearer perspective on the mechanism underlying our abilities for emotional understanding and on cases in which these abilities are amiss, as in autistic spectrum disorders.

Construction of a Danish CDI short form for language screening at the age of 36 months: methodological considerations and results

Several research groups have previously constructed short forms of the MacArthur-Bates Communicative Development Inventories (CDI) for different languages. We consider the specific aim of constructing such a short form to be used for language screening in a specific age group. We present a novel strategy for the construction, which is applicable if results from a population-based study using the CDI long form are available for this age group. The basic approach is to select items in a manner implying a left-skewed distribution of the summary score and hence a reliable discrimination among children in the lower end of the distribution despite the measurement error of the instrument. We report on the application of the strategy in constructing a Danish CDI short form and present some results illustrating the validity of the short form. Finally we discuss the choice of the most appropriate age for language screening based on a vocabulary score.

Insights into brain development from neurogenetic syndromes: evidence from fragile X syndrome, Williams syndrome, Turner syndrome and velocardiofacial syndrome

Over the past few decades, behavioral, neuroimaging and molecular studies of neurogenetic conditions, such as Williams, fragile X, Turner and velocardiofacial (22q11.2 deletion) syndromes, have led to important insights regarding brain development. These investigations allow researchers to examine "experiments of nature" in which the deletion or alteration of one gene or a contiguous set of genes can be linked to aberrant brain structure or function. Converging evidence across multiple imaging modalities has now begun to highlight the abnormal neural circuitry characterizing many individual neurogenetic syndromes. Furthermore, there has been renewed interest in combining analyses across neurogenetic conditions in order to search for common organizing principles in development. In this review, we highlight converging evidence across syndromes from multiple neuroimaging modalities, with a particular emphasis on functional imaging. In addition, we discuss the commonalities and differences pertaining to selective deficits in visuospatial processing that occur across four neurogenetic syndromes. We suggest avenues for future exploration, with the goal of achieving a deeper understanding of the neural abnormalities in these affected populations.

The psychophysics of visual motion and global form processing in autism

Several groups have recently reported that people with autism may suffer from a deficit in visual motion processing and proposed that these deficits may be related to a general dorsal stream dysfunction. In order to test the dorsal stream deficit hypothesis, we investigated coherent and biological motion perception as well as coherent form perception in a group of adolescents with autism and a group of age-matched typically developing controls. If the dorsal stream hypothesis were true, we would expect to document deficits in both coherent and biological motion processing in this group but find no deficit in coherent form perception. Using the method of constant stimuli and standard psychophysical analysis techniques, we measured thresholds for coherent motion, biological motion and coherent form. We found that adolescents with autism showed reduced sensitivity to both coherent and biological motion but performed as well as age-matched controls during coherent form perception. Correlations between intelligence quotient and task performance, however, appear to drive much of the group difference in coherent motion perception. Differences between groups on coherent motion perception did not remain significant when intelligence quotient was controlled for, but group differences in biological motion perception were more robust, remaining significant even when intelligence quotient differences were accounted for. Additionally, aspects of task performance on the biological motion perception task were related to autism symptomatology. These results do not support a general dorsal stream dysfunction in adolescents with autism but provide evidence of a more complex impairment in higher-level dynamic attentional processes.

How vision matters for individuals with hearing loss

Hearing loss has obvious implications for communication and auditory functioning. A less obvious implication of hearing loss is its effect on the remaining sensory systems, particularly vision. This paper will review research demonstrating that deafness affects the development of specific visual functions and their neural substrates, including motion processing, face processing, and attention to peripheral space. Implications of this cross-modal plasticity are discussed in a review of studies with cochlear implant recipients. This latter work suggests that visual speech perception skills that develop during periods of deafness have positive implications for later perception of auditory speech. These effects are discussed in light of multimodal processing and perceptual learning.

Brain abnormalities in Williams syndrome: a review of structural and functional magnetic resonance imaging findings

Williams syndrome (WS) is rare genetic form of mental retardation caused by a microdeletion on chromosome 7q11.23 that causes cognitive impairment and a variety of physical abnormalities. MRI studies of WS have demonstrated a series of brain abnormalities, including decreased brain size, with a relatively greater decrease in the volume of the cerebral white matter volume as compared to the cerebral gray matter. Moreover there is evidence that the posterior cerebrum is more affected in that persons with WS have a greater ratio of frontal to posterior regional volume. These findings are further supported by automated analyses that have shown reduced gray matter density in the superior parietal lobe areas. Functional MRI studies have demonstrated hypofunction immediately adjacent to, and anterior to, the intraparietal sulcus, a region in which structural brain differences had been identified. These anatomical and functional differences are consistent with the neuropsychological profile of WS - in particular, with evidence of dorsal stream visual processing deficits. To date, however, studies have always been performed in comparison to intellectually average controls. It is not clear, therefore, if findings are specific to the WS population or whether they represent a morphological disturbance characteristic of mental retardation, irrespective of genetic etiology. In this article, we reviewed recent advances underlying the structural and functional neural substrate of WS in Medical Literature Analysis and Retrieval System Online (MEDLINE; 1997-2007).

Retinotopically defined primary visual cortex in Williams syndrome

Williams syndrome, caused by a hemizygous microdeletion on chromosome 7q11.23, is characterized by severe impairment in visuospatial construction. To examine potential contributions of early visual processing to this cognitive problem, we functionally mapped the size and neuroanatomical variability of primary visual cortex (V1) in high-functioning adults with Williams syndrome and age- and IQ-matched control participants from the general population by using fMRI-based retinotopic mapping and cortical surface models generated from high-resolution structural MRI. Visual stimulation, consisting of rotating hemicircles and expanding rings, was used to retinotopically define early visual processing areas. V1 boundaries based on computed phase and field sign maps were used to calculate the functional area of V1. Neuroanatomical variability was assessed by computing overlap maps of V1 location for each group on standardized cortical surfaces, and non-parametric permutation test methods were used for statistical inference. V1 did not differ in size between groups, although its anatomical boundaries were more variable in the group with Williams syndrome. V1 overlap maps showed that the average centres of gravity for the two groups were similarly located near the fundus of the calcarine fissure, approximately 25 mm away from the most posterior aspect of the occipital lobe. In summary, our functional definition of V1 size and location indicates that recruitment of primary visual cortex is grossly normal in Williams syndrome, consistent with the notion that neural abnormalities underlying visuospatial construction arise at later stages in the visual processing hierarchy.

Gait function in adults with Williams syndrome

Despite early neurological reports of gait abnormalities in Williams syndrome (WS), a rare genetically based neurodevelopmental disorder, there has not yet been any systematic investigation of gait dysfunction in this disorder. The current study examined the gait characteristics in adults with WS and a neurologically normal control group as they walked at self-selected slow, preferred and fast speeds using the GAITRite walkway. The WS group showed hypokinetic gait, which manifested as reduced gait speed and stride length, but with a disproportionate increase in cadence (stepping frequency) as speed was increased. The WS group also showed increased variability of stride length and a broad based stepping pattern implicating a compensatory strategy for postural instability. Performance IQ correlated significantly with stride length in the WS group. While these results should be considered preliminary due to the small sample size, these findings have implications for our understanding of the neural basis of gait dysfunction in WS.

Social relevance boosts context processing in Williams syndrome

The aim of the present study was to determine whether individuals with Williams syndrome (WS) are able to recognize facial expressions of emotion and objects missing on the basis of contextual cues. Sixteen individuals with WS were compared to typically developing individuals matched on chronological and mental age. WS group performed significantly lower than both control groups in object recognition. By contrast, no such group differences were found in facial expression recognition, suggesting that individuals with WS do have the ability to process contextual cues. However, this ability seems to be boosted when they are to process socially relevant cues.

Early vocabulary development in Danish and other languages: a CDI-based comparison

The main objective of this paper is to describe the trajectory of Danish children's early lexical development relative to other languages, by comparing a Danish study based on the Danish adaptation of The MacArthur-Bates Communicative Development Inventories (CDI) to 17 comparable CDI-studies. The second objective is to address the feasibility of cross-linguistic CDI-comparisons. The main finding is that the developmental trend of Danish children's early lexical development is similar to trends observed in other languages, yet the vocabulary comprehension score in the Danish children is the lowest across studies from age 1 ; 0 onwards. We hypothesize that the delay is related to the nature of Danish sound structure, which presents Danish children with a harder task of segmentation. We conclude that CDI-studies are an important resource for cross-language studies, but reporting of studies needs to be standardized and the availability of published data improved in order to make comparisons more straightforward.

The role of color cues in facilitating accurate and rapid location of aided symbols by children with and without down syndrome

PURPOSE

This research examined how the color distribution of symbols within a visual aided augmentative and alternative communication array influenced the speed and accuracy with which participants with and without Down syndrome located a target picture symbol.

METHOD

Eight typically developing children below the age of 4 years, 8 typically developing children over the age of 4 years, and 10 children with Down syndrome participated. Participants were asked to find a target line drawing among an array of 12. Line drawings represented either foods (e.g., grapes, cherries), clothing (e.g., a red shirt, a yellow shirt), or activities (e.g., soccer, swimming). In one condition, symbols that shared a color were clustered together, creating a subgroup within which to search. In another condition, symbols that shared a color were distributed across the display, allowing each to appear individually. Dependent measures were accuracy and speed of finding the target symbol.

RESULTS

Clustering same-color symbols facilitated the speed of locating the target for all participants, and facilitated search accuracy in the younger preschool children and participants with Down syndrome. These effects held when targets were foods, clothing, or activities.

CONCLUSION

Clinicians should consider the internal color of visual symbols when constructing aided symbol displays, at least for children with Down syndrome. Further research is needed on a number of dimensions, however, including visual processing in other etiological categories, the role of background color, and the relation of color to other stimulus dimensions.

White matter tract integrity and intelligence in patients with mental retardation and healthy adults

It is well known that brain structures correlate with intelligence but the association between the integrity of brain white matter tracts and intelligence in patients with mental retardation (MR) and healthy adults remains unknown. The aims of this study are to investigate whether the integrity of corpus callosum (CC), cingulum, uncinate fasciculus (UF), optic radiation (OR) and corticospinal tract (CST) are damaged in patients with MR, and to determine the correlations between the integrity of these tracts and full scale intelligence quotient (FSIQ) in both patients and controls. Fifteen MR patients and 79 healthy controls underwent intelligence tests and diffusion tensor imaging examinations. According to the FSIQ, all healthy controls were divided into general intelligence (GI: FSIQ<120; n=42) and high intelligence (HI: FSIQ> or =120; n=37) groups. Intelligence was assessed by Chinese Revised Wechsler Adult Intelligence Scale, and white matter tract integrity was assessed by fractional anisotropy (FA). MR patients showed significantly lower FA than healthy controls in the CC, UF, OR and CST. However, GI subjects only demonstrated lower FA than HI subjects in the right UF. Partial correlation analysis controlling for age and sex showed that FSIQ scores were significantly correlated with the FA of the bilateral UF, genu and truncus of CC, bilateral OR and left CST. While FSIQ scores were only significantly correlated with the FA of the right UF when further controlling for group. This study indicate that MR patients show extensive damage in the integrity of the brain white matter tracts, and the right UF is an important neural basis of human intelligence.

Orientation and affective expression effects on face recognition in Williams syndrome and autism

We sought to clarify the nature of the face processing strength commonly observed in individuals with Williams syndrome (WS) by comparing the face recognition ability of persons with WS to that of persons with autism and to healthy controls under three conditions: Upright faces with neutral expressions, upright faces with varying affective expressions, and inverted faces with neutral expressions. No differences were observed under the upright/neutral expression condition. However, the WS group was more accurate than the autism group when discriminating upright faces with varying affective expressions, whereas the opposite pattern emerged when discriminating inverted faces. We interpret these differences as a reflection of the contrasting social features of the two syndromes.

A visual skills inventory for children with neurological impairments

Children with neurological impairments often have visual deficits that are difficult to quantify. We have compared visual skills evaluated by carers with results of a comprehensive visual assessment. Participants were 76 children with mild to profound intellectual and/or motor impairment (33 males, 43 females; age range 7mo-16y; mean age 5y 1mo [SD 4y 2mo]) who completed a visual skills inventory before attending a special vision clinic. The inventory included 16 questions about visual skills and responses to familiar situations. Responses were augmented by taking a structured clinical history, compared with visual evoked potential (VEP) and/or acuity card measures of visual acuity, and examined using exploratory factor analysis. Acuity ranged from normal to no light perception, and was positively associated with responses to individual questions. After excluding four uninformative questions, an association between the remaining questions and two significant independent factors was found. Factor 1 was associated with questions about visual recognition (e.g. 'Does your child see a small silent toy?') and these items were correlated with both the VEP and acuity card thresholds. Factor 2 was associated primarily with questions about visually mediated social interactions (e.g. 'Does he/she return your silent smile?'). Evaluation of visual skills in children with neurological impairment can provide valid information about the quality of children's vision. Questions with the highest validity for predicting vision are identified.

Studies of age-correlated features of cognitive-behavioral development in children and adolescents with genetic disorders

Studies of age-related features of cognitive-behavioral deficits produced by genetic mutations permit us to draw inferences about how brain development may be related cognitive ability as the child ages. Except for Down syndrome (DS) and the fragile X mutation (FRAXA), little is known about the longitudinal changes in cognitive-behavioral development in individuals with genetic abnormalities producing learning disabilities (LD) or mental retardation (MR). The purpose of this prospective study was to compare and contrast age related to cognitive abilities, adaptive and maladaptive behaviors in children and adolescents in the same age range, diagnosed with one of three genetic disorders: the FRAXA mutation, Neurofibromatosis type 1 (NF1) or Williams-Beuren syndrome (WBS). We also sought to examine whether cognitive-behavioral abilities associated with these three genetic disorders were related systematically to age. We examined 108 children, ages 4-15 years, with FRAXA, WBS, or NF1. Results show that there is a significant negative correlation between age and IQ, and between age and adaptive behavior (DQ) scores, in children with FRAXA and WBS, but not in children with NF1. All three groups of children have unusually high proportions of maladaptive behavior, ranging from 1/6 children with NF1 to 2/3 children with FRAXA. Cognitive and adaptive behavior profiles of children with FRAXA and WBS were also surprisingly similar. Our findings suggest the need for examining longitudinal developmental cognitive-behavioral changes in children and adolescents with all genetic disorders that produce LD or MR.

The tortuous route from genes to behavior: A neuroconstructivist approach

In their excitement at using the human genome project to uncover the functions of specific genes, researchers have often ignored one fundamental factor: the gradual process of ontogenetic development. The view that there might be a gene for spatial cognition or language has emanated from a focus on the structure of the adult brain in neuropsychological patients whose brains were fully and normally developed until their brain insult. The developing brain is very different. It starts out highly interconnected across regions and is neither localized nor specialized at birth, allowing interaction with the environment to play an important role in gene expression and the ultimate cognitive phenotype. This article takes a neuroconstructivist perspective, arguing that domain-specific end states can stem from more domain-general start states, that associations may turn out to be as informative as dissociations, and that genetic mutations that alter the trajectory of ontogenetic development can inform nature/nurture debates.

To modulate or not to modulate: Differing results in uniquely shaped Williams syndrome brains

Voxel based morphometry (VBM) studies of Williams syndrome (WS) have demonstrated remarkably consistent findings of reduced posterior parietal gray matter compared to typical controls. Other WS VBM findings have been inconsistent, however. In particular, different findings have been reported for hypothalamus and orbitofrontal gray matter regions. We examined a sample of 8 WS and 9 control adults and show that the hypothalamus and orbitofrontal cortex results depend on whether the images undergo Jacobian modulation. Deformation based morphometry (DBM) analysis demonstrated that major brain shape differences between the groups accounted for the Jacobian modulated gray matter findings. These results indicate that cautious interpretations of modulated gray matter findings are warranted when there are gross shape and size differences between experimental groups. This study demonstrates the importance of methodological choices towards understanding a disorder like WS, but also highlights the consistency of parietal lobe, orbitofrontal, and midbrain findings for this disorder across methodologies, participants, and research groups.

Neural mechanisms in Williams syndrome: a unique window to genetic influences on cognition and behaviour

Williams syndrome, a rare disorder caused by hemizygous microdeletion of about 28 genes on chromosome 7q11.23, has long intrigued neuroscientists with its unique combination of striking behavioural abnormalities, such as hypersociability, and characteristic neurocognitive profile. Williams syndrome, therefore, raises fundamental questions about the neural mechanisms of social behaviour, the modularity of mind and brain development, and provides a privileged setting to understand genetic influences on complex brain functions in a 'bottom-up' way. We review recent advances in uncovering the functional and structural neural substrates of Williams syndrome that provide an emerging understanding of how these are related to dissociable genetic contributions characterized both in special participant populations and animal models.

Do children with Williams syndrome fail to process visual configural information?

Configural visual abilities in thirteen children with Williams syndrome (WS) compared to 13 children matched on mental age and 13 children matched on chronological age. Configural abilities were tested through four tasks (1) Silhouette (2) Fragmented (3) Mooney and (4) overlapping figures. In the first three tasks, it was necessary to take into account the global information, as the identification of the figures could not be established through a local analysis. In the fourth task, the global configuration of the display had to be ignored. Configural skills seem appropriate in the WS population. A possible dissociation between perceptual and visuo-constructive configural competences is discussed.

Dorsal-stream motion processing deficits persist into adulthood in Williams syndrome

Previous studies of children with Williams syndrome (WS) have found a specific deficit in dorsal cortical stream function, indicated by poor performance in coherence thresholds for motion compared to form. Here we investigated whether this is a transient developmental feature or a persisting aspect of cerebral organization in WS. Motion and form coherence thresholds were tested in a group of 45 WS individuals aged 16-42 years, and 19 normal adult controls. Although there was considerable variation in the coherence thresholds across individuals with WS, the WS group showed overall worse performance than controls. A significant group x threshold condition interaction showed a substantially greater performance deficit for motion than for form coherence in the WS group relative to controls. This result suggests that the motion deficit is an enduring feature in WS and is a marker for one aspect of dorsal-stream vulnerability.

Associations between the developmental trajectories of visual scanning and disengagement of attention in infants

The relation between the developmental trajectories of visual scanning and disengagement of attention and gaze were examined throughout early infancy. A sample of 10 infants carried out a scanning and a disengagement task with the same visual stimuli six times between 6 and 26 weeks of age. Frequency and latency measures were analyzed using multivariate multilevel models and Monte Carlo analyses. The results suggest that the ability to scan a face or an abstract stimulus evolves slightly earlier than the ability to shift gaze to a newly appeared target in the periphery. This is consistent with the account that the parvocellular stream becomes functional slightly before the magnocellular stream. The study revealed no indications of a positive association between the development of scanning and disengagement on the level of the individual infant. Scanning and disengagement change scores contrasted more with one another than could be expected on the basis of chance. This implies that the magnocellular and the parvocellular stream develop rather independently up to the age of 26 weeks.

Motion processing specialization in Williams syndrome

Williams syndrome (WS) is a rare genetic disorder characterized by severe spatial deficits and relatively spared language. Although initial research suggested that WS entails a generalized motion processing deficit, later work demonstrated intact biological motion perception in people with WS, reflecting a sparing of a specific motion perception system. The present study examined whether this sparing is unique to biological motion, or extends to other motion tasks as well. WS children and adults and normal controls were tested to examine developmental changes across a variety of motion tasks. Results indicated that WS individuals performed at normal levels for motion coherence and biological motion tasks but had elevated thresholds for the 2-D form-from-motion task, a profile that extended into adulthood. These findings provide evidence that a genetic impairment can lead to a selective motion processing deficit and argue against characterizing WS as including a general motion processing impairment. The nature of the motion deficit is considered, including the implications for WS dorsal/ventral processing.

Visual depth processing in Williams–Beuren syndrome

Patients with Williams-Beuren Syndrome (WBS, also known as Williams Syndrome) show many problems in motor activities requiring visuo-motor integration, such as walking stairs. We tested to what extent these problems might be related to a deficit in the perception of visual depth or to problems in using this information in guiding movements. Monocular and binocular visual depth perception was tested in 33 patients with WBS. Furthermore, hand movements to a target were recorded in conditions with and without visual feedback of the position of the hand. The WBS group was compared to a group of control subjects. The WBS patients were able to perceive monocular depth cues that require global processing, but about 49% failed to show stereopsis. On average, patients with WBS moved their hand too far when no visual feedback on hand position was given. This was not so when they could see their hand. Patients with WBS are able to derive depth from complex spatial relationships between objects. However, they seem to be impaired in using depth information for guiding their movements when deprived of visual feedback. We conclude that the problems that WBS patients have with tasks such as descending stairs are not due to an inability to judge distance.

Relative sparing of primary auditory cortex in Williams Syndrome

Williams Syndrome (WS) is a neurodevelopment disorder associated with a hemizygous deletion on chromosome 7. WS is characterized with mental retardation, severe visual-spatial deficits, relative language preservation, and excellent facial recognition. Distinctive auditory features include musical ability, heightened sound sensitivity, and specific patterns of auditory evoked potentials. These features have led to the hypothesis that the dorsal forebrain is more affected than the ventral. Previously, we reported primary visual area 17 abnormalities in rostral striate cortex, a region contributing to the dorsal visual pathway. Based on the dorsal-ventral hypothesis, and language and auditory findings, we predicted a more normal histometric picture in auditory area 41. We used an optical dissector method to measure neurons in layers II-VI of area 41 in right and left hemispheres of the same 3 WS and 3 control brains used in the area 17 study. There was a hemisphere by diagnosis interaction in cell packing density (CPD) in layer IV and in cell size in layer III between WS and control brains. Post hoc analysis disclosed in control brains, but not WS, a layer IV left > right asymmetry in CPD, and a layer III left < right asymmetry in cell size. WS brains showed more large neurons bilaterally in layer II and in left layer VI. Histometric alterations in area 41 were less widespread than rostral visual cortex. Also, there was less asymmetry in the WS brain. We interpret layers II and VI differences as reflecting increased limbic connectivity in primary auditory cortex of WS.

The influences of visibility and anomalous integration processes on the perception of global spatial form versus motion in human amblyopia

Do amblyopes demonstrate general irregularities in processes of global image integration? Or are these anomalies stimulus specific? To address these questions we employed directly analogous global-orientation and global-motion stimuli using a method that allows us to factor out any influence of the low-level visibility loss [Simmers, A. J., Ledgeway, T., Hess, R. F., & McGraw, P. V. (2003). Deficits to global motion processing in human amblyopia. Vision Research 43, pp. 729-738]. The combination of orientation and motion coherence thresholds reported here provides comparable psychophysical measures of global processing by spatial-sensitive and motion-sensitive mechanisms in the amblyopic visual system. The results show deficits in both global-orientation and global-motion processing in amblyopia, which appear independent of any low-level visibility loss, but with the most severe deficit affecting the extraction of global motion. This provides evidence for the existence of a dominant temporal processing deficit in amblyopia.

An experiment of nature: brain anatomy parallels cognition and behavior in Williams syndrome

Williams syndrome (WS) is a neurogenetic-neurodevelopmental disorder characterized by a highly variable and enigmatic profile of cognitive and behavioral features. Relative to overall intellect, affected individuals demonstrate disproportionately severe visual-spatial deficits and enhanced emotionality and face processing. In this study, high-resolution magnetic resonance imaging data were collected from 43 individuals with WS and 40 age- and gender-matched healthy controls. Given the distinct cognitive-behavioral dissociations associated with this disorder, we hypothesized that neuroanatomical integrity in WS would be diminished most in regions comprising the visual-spatial system and most "preserved" or even augmented in regions involved in emotion and face processing. Both volumetric analysis and voxel-based morphometry were used to provide convergent approaches for detecting the hypothesized WS neuroanatomical profile. After adjusting for overall brain volume, participants with WS showed reduced thalamic and occipital lobe gray matter volumes and reduced gray matter density in subcortical and cortical regions comprising the human visual-spatial system compared with controls. The WS group also showed disproportionate increases in volume and gray matter density in several areas known to participate in emotion and face processing, including the amygdala, orbital and medial prefrontal cortices, anterior cingulate, insular cortex, and superior temporal gyrus. These findings point to specific neuroanatomical correlates for the unique topography of cognitive and behavioral features associated with this disorder.

Foreshortened Dorsal Extension of the Central Sulcus in Williams Syndrome

Williams syndrome (WMS) is a genetic condition resulting from a hemideletion on chromosome 7 that causes cognitive impairment, and a variety of growth and physical abnormalities. Little is currently known about brain morphology in WMS, although one recent MRI report suggested that the central sulcus was abnormally short on its dorsal end compared to normal IQ controls. We sought to replicate this finding in a group of 28 persons with WMS in comparison to both an age and sex matched normal IQ control group (n = 22). In addition, we sought to test the specificity of this finding by a further comparison to an IQ matched control group (n = 20). Using high resolution isotropic voxel MRI, the dorsal and ventral extension of the central sulcus was traced and the distance from the interhemispheric and sylvian fissures was measured. The dorsal extension of the central sulcus in both hemispheres was significantly more distant from the interhemispheric fissure in WMS compared to the lower IQ group and to the normal control group (p's < 0.001). There was no significant difference between groups in the ventral end of the central sulcus. These results suggest that the abnormal dorsal end of the central sulcus may be a specific characteristic of WMS not shared with general mental retardation or low IQ.

Neuropsychological profile of Italians with Williams syndrome: an example of a dissociation between language and cognition?

Important claims have been made regarding the contrasting profiles of linguistic and cognitive performance observed in two genetically based syndromes, Williams syndrome (WS) and Down syndrome (DS). Earlier studies suggested a double dissociation, with language better preserved than nonverbal cognition in children and adults with WS, and an opposite profile in children and adults with DS. More recent studies show that this initial characterization was too simple, and that qualitatively different patterns of deficit observed within both language and visual-spatial cognition, in both groups. In the present study, large samples of children and adolescents with WS and age-matched DS are compared with typically developing (TD) controls matched to WS in mental age, on receptive and expressive lexical and grammatical abilities, semantic and phonological fluency, digit span and nonverbal visual-spatial span, and on 2 visual-spatial construction tasks. Study 1 confirmed distinct profiles of sparing and impairment for the 2 groups, within as well as between language and nonlinguistic domains, even after IQ variations were controlled. In Study 2 we compared performance of the children, adolescents and young adults with DS and WS included in the first study, divided on the basis of the chronological age of the participants (under 8 years; over 12 years). Although it is important to stress that these are cross-sectional rather than longitudinal data, the results demonstrated that the profile of younger children is different in respect to those of the older children; initial states of the system cannot be inferred by the final state. Possible neural substrates for these profiles and trajectories are discussed.

Visual perceptual impairment in children at 5 years of age with perinatal haemorrhagic or ischaemic brain damage in relation to cerebral magnetic resonance imaging

Children with perinatally acquired parenchymal haemorrhage are thought to have better visual perceptual skills than those with leukomalacia. We examined seven prematurely born children with parenchymal haemorrhage and 14 with grades 2-4 leukomalacia, at the age of 5 years. Clinical and magnetic resonance imaging parameters were related to visual perceptual performance assessed with the L94, using performance age. Belonging to the leukomalacia group, the inability to walk, a diminished peritrigonal white matter, a high degree of gliosis and cortical damage were associated with poorer visuo-perceptual skills. Enlarged lateral ventricles, confirming the findings of Melhelm (Radiology 214 (2000) 199), were associated with both cognitive, perceptual and motor problems and probably reflect the considerable extent of the brain damage. Specific factors protecting against visual perceptual impairment were a preserved volume of the right optical radiation and of the splenium of the corpus callosum. Children with leukomalacia are at considerable risk of visual perceptual impairment. Children with right-sided parenchymal haemorrhages also appear to be at risk although they function much better due to better motor and cognitive skills.

Reading and Phonological Awareness in Williams Syndrome

This article describes the relationship between reading, phonological awareness abilities (PA), and intelligence in a group of 16 individuals with Williams syndrome (WS) and in a group of 16 typically developing children, matched for mental age. The individuals with WS were impaired in passage comprehension, in some areas of PA investigated (syllable deletion and rhyme detection), and in nonword reading accuracy, a measure of grapheme-phoneme conversion. This latter finding is relevant, considering that in Italy regular print-to-sound correspondence is the most practiced teaching routine in the early phases of learning to read.

Normal and anomalous development of visual motion processing: motion coherence and 'dorsal-stream vulnerability'

Directional motion processing is a pervasive and functionally important feature of the visual system. Behavioural and VEP studies indicate that it appears as a cortical function after about 7 weeks of age, with global processing, motion based segmentation, and the use of motion in complex perceptual tasks emerging shortly afterwards. A distinct, subcortical motion system controls optokinetic nystagmus (OKN) from birth, showing characteristic monocular asymmetries which disappear as binocular cortical function takes over in normal development. Asymmetries in cortical responses are linked to this interaction in a way that is not yet fully understood. Beyond infancy, a range of developmental disorders show a deficit of global motion compared to global form processing which we argue reflects a general 'dorsal-stream vulnerability'.

Disorders of motion and depth

Damage to the human homologue of area MT produces a motion perception deficit similar to that found in the monkey with MT lesions. Even temporary disruption of MT processing with transcranial magnetic stimulation can produce a temporary akinetopsia [127]. Motion perception deficits, however, also are found with a variety of subcortical lesions and other neurologic disorders that can best be described as causing a disconnection within the motion processing stream. The precise role of these subcortical structures, such as the cerebellum, remains to be determined. Simple motion perception, moreover, is only a part of MT function. It undoubtedly has an important role in the perception of depth from motion and stereopsis [112]. Psychophysical studies using aftereffects in normal observers suggest a link between stereo mechanisms and the perception of depth from motion [9-11]. There is even a simple correlation between stereo acuity and the perception of depth from motion [128]. Future studies of patients with cortical lesions will take a closer look at depth perception in association with motion perception and should provide a better understanding of how motion and depth are processed together.

Visual performance in specific syndromes associated with intellectual disability

PURPOSE

To report visual performance in adults with specific causes of intellectual disability (ID) and to compare the test results to published reports.

METHODS

In a large-scale multicenter epidemiologic study of sensory impairments in 1598 adults with ID, the authors performed ocular assessments in 1539 persons. They compared the test results of those with five specific genetic disorders (Angelman syndrome, Prader-Willi syndrome, fragile X syndrome, Williams-Beuren syndrome, and tuberous sclerosis).

RESULTS

An overrepresentation of strabismus, low vision, and refractive errors was found. Apart from fragile X syndrome and Prader-Willi syndrome (with in general mild to moderate ID), the other syndrome groups contained one or more subjects with visual impairment or blindness. A number of them had never been seen by an ophthalmologist.

CONCLUSIONS

The authors confirm a number of ocular features previously reported by other studies and suggest some additional ocular features. They found increased frequencies of treatable ophthalmologic conditions in the subgroups. Because reliable ocular assessment is feasible for 85% of persons with ID, the results are an incentive to address visual functioning in people with ID in order to correct ocular problems and maximize their possibilities.

Word reading and reading-related skills in adolescents with Williams syndrome

BACKGROUND

Individuals with Williams syndrome have good spontaneous language despite low levels of intelligence. This study explores the relationship between intelligence, word decoding and reading-related skills in 20 individuals with Williams syndrome.

METHODS

In addition to the KBIT, the participants were administered standardized measures of reading, vocabulary, rapid naming, phonological skills and an experimental measure of rhyme judgement.

RESULTS

There was wide variability in the reading achievement among the individuals with WS. While some participants were unable to recognize letters of the alphabet, others scored within the normal range of tests of single word reading and decoding. Reading scores were correlated with intelligence as measured on KBIT matrices but not with the vocabulary measures. Reading also correlated with phonological awareness tasks yet, surprisingly, not with rapid naming.

CONCLUSION

It is suggested that in individuals with retardation, intelligence rather than language and language-related skills predict achievements in word reading.

A test battery of child development for examining functional vision (ABCDEFV)

A battery of 22 tests is described, intended to give an integrated assessment of children's functional visual capacities between birth and four years of age. As well as sensory visual measures such as acuity, visual fields and stereopsis, the battery is intended to tap a range of perceptual, motor, spatial and cognitive aspects of visual function. Tests have been drawn from practice in ophthalmology and orthoptics, vision research, paediatric neurology, and developmental psychology to give an overall view of children's visual competences for guidance in diagnosis, further investigation, management and rehabilitation of children with developmental disorders. 'Core vision tests' require no motoric capacities beyond saccadic eye movements or linguistic skills and so assess basic visual capacities in children of any age. 'Additional tests' have age-specific requirements and are designed to pinpoint specific deficits in the perceptual, visuo-motor and spatio-cognitive domains. Normative data are reported on nine age groups between 0-6 weeks and 31-36 months, each including 32-43 typically developing children. Pass/fail criteria for each test are defined. These data allow the selection of a subset of tests for each age group which are passed by at least 85% of normally developing children, and so are appropriate for defining normal development. The normalized battery has been applied to a range of at-risk and clinical groups. Aspects of children's visual performance are discussed in relation to neurobiological models of visual development.

Cross-modal plasticity: where and how?

Animal studies have shown that sensory deprivation in one modality can have striking effects on the development of the remaining modalities. Although recent studies of deaf and blind humans have also provided convincing behavioural, electrophysiological and neuroimaging evidence of increased capabilities and altered organization of spared modalities, there is still much debate about the identity of the brain systems that are changed and the mechanisms that mediate these changes. Plastic changes across brain systems and related behaviours vary as a function of the timing and the nature of changes in experience. This specificity must be understood in the context of differences in the maturation rates and timing of the associated critical periods, differences in patterns of transiently existing connections, and differences in molecular factors across brain systems.

Intact perception of biological motion in the face of profound spatial deficits: Williams syndrome

Williams syndrome (WS) is a rare genetic disorder that results in profound spatial cognitive deficits. We examined whether individuals with WS have intact perception of biological motion, which requires global spatial integration of local motion signals into a unitary percept of a human form. Children with WS, normal mental-age-matched children, and normal adults viewed point-light-walker (PLW) displays portraying a human figure walking to the left or right. Children with WS were as good as or better than control children in their ability to judge the walker's direction, even when it was masked with dynamic noise that mimicked the local motion of the PLW lights. These results show that mechanisms underlying the perception of at least some kinds of biological motion are unimpaired in children with WS. They provide the first evidence of selective sparing of a specialized spatial system in individuals with a known genetic impairment.