Orientation perception in Williams Syndrome: discrimination and integration

An opposing function of paralogs in balancing developmental synapse maturation

The disc-large (DLG)-membrane-associated guanylate kinase (MAGUK) family of proteins forms a central signaling hub of the glutamate receptor complex. Among this family, some proteins regulate developmental maturation of glutamatergic synapses, a process vulnerable to aberrations, which may lead to neurodevelopmental disorders. As is typical for paralogs, the DLG-MAGUK proteins postsynaptic density (PSD)-95 and PSD-93 share similar functional domains and were previously thought to regulate glutamatergic synapses similarly. Here, we show that they play opposing roles in glutamatergic synapse maturation. Specifically, PSD-95 promoted, whereas PSD-93 inhibited maturation of immature α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-type glutamate receptor (AMPAR)-silent synapses in mouse cortex during development. Furthermore, through experience-dependent regulation of its protein levels, PSD-93 directly inhibited PSD-95's promoting effect on silent synapse maturation in the visual cortex. The concerted function of these two paralogs governed the critical period of juvenile ocular dominance plasticity (jODP), and fine-tuned visual perception during development. In contrast to the silent synapse-based mechanism of adjusting visual perception, visual acuity improved by different mechanisms. Thus, by controlling the pace of silent synapse maturation, the opposing but properly balanced actions of PSD-93 and PSD-95 are essential for fine-tuning cortical networks for receptive field integration during developmental critical periods, and imply aberrations in either direction of this process as potential causes for neurodevelopmental disorders.

Supramodal agnosia for oblique mirror orientation in patients with periventricular leukomalacia

Periventricular leukomalacia (PVL) is characterized by focal necrosis at the level of the periventricular white matter, often observed in preterm infants. PVL is frequently associated with motor impairment and with visual deficits affecting primary stages of visual processes as well as higher visual cognitive abilities. Here we describe six PVL subjects, with normal verbal IQ, showing orientation perception deficits in both the haptic and visual domains. Subjects were asked to compare the orientation of two stimuli presented simultaneously or sequentially, using both a two alternative forced choice (2AFC) orientation-discrimination and a matching procedure. Visual stimuli were oriented gratings or bars or collinear short lines embedded within a random pattern. Haptic stimuli comprised two rotatable wooden sticks. PVL patients performed at chance in discriminating the oblique orientation, both for visual and haptic stimuli. Moreover when asked to reproduce the oblique orientation, they often oriented the stimulus along the symmetric mirror orientation. The deficit generalized to stimuli varying in many low level features, was invariant for spatiotopic object orientation, and also occurred for sequential presentations. The deficit was specific to oblique orientations, and not for horizontal or vertical stimuli. These findings show that PVL can affect a specific network involved with the supramodal perception of mirror symmetry orientation.

Basic visual perceptual processes in children with typical development and cerebral palsy: The processing of surface, length, orientation, and position

The present study aims to assess how the processing of basic visual perceptual (VP) components (length, surface, orientation, and position) develops in typically developing (TD) children (n = 215, 4-14 years old) and adults (n = 20, 20-25 years old), and in children with cerebral palsy (CP) (n = 86, 5-14 years old) using the first four subtests of the Battery for the Evaluation of Visual Perceptual and Spatial processing in children. Experiment 1 showed that these four basic VP processes follow distinct developmental trajectories in typical development. Experiment 2 revealed that children with CP present global and persistent deficits for the processing of basic VP components when compared with TD children matched on chronological age and nonverbal reasoning abilities.

Spatial Language and the Embedded Listener Model in Parents' Input to Children

Language is a collaborative act: To communicate successfully, speakers must generate utterances that are not only semantically valid but also sensitive to the knowledge state of the listener. Such sensitivity could reflect the use of an "embedded listener model," where speakers choose utterances on the basis of an internal model of the listener's conceptual and linguistic knowledge. In this study, we ask whether parents' spatial descriptions incorporate an embedded listener model that reflects their children's understanding of spatial relations and spatial terms. Adults described the positions of targets in spatial arrays to their children or to the adult experimenter. Arrays were designed so that targets could not be identified unless spatial relationships within the array were encoded and described. Parents of 3-4-year-old children encoded relationships in ways that were well-matched to their children's level of spatial language. These encodings differed from those of the same relationships in speech to the adult experimenter (Experiment 1). In contrast, parents of individuals with severe spatial impairments (Williams syndrome) did not show clear evidence of sensitivity to their children's level of spatial language (Experiment 2). The results provide evidence for an embedded listener model in the domain of spatial language and indicate conditions under which the ability to model listener knowledge may be more challenging.

Performance on the Kaufman Brief Intelligence Test-2 by Children With Williams Syndrome

We describe the performance of 292 4- to 17-year-olds with Williams syndrome (WS) on the Kaufman Brief Intelligence Test-2 (KBIT-2; Kaufman & Kaufman, 2004). Mean IQ Composite, Verbal standard score (SS), and Nonverbal SS were in the borderline range relative to the general population, with variability similar to the general population. Correlations between SSs and CA were close to 0, with no significant sex differences. There was a significant effect of maternal education on Verbal SS. The KBIT-2 appropriately captures the full range of performance of 8- to 17-year-olds with WS for the abilities measured and of all but the very lowest-functioning 5- to 7-year-olds. However, the KBIT-2 does not contain easy enough items to adequately assess the abilities of the lowest quartile of 4-year-olds.

Drawing ability in typical and atypical development; colour cues and the effect of oblique lines

BACKGROUND

Individuals with Williams syndrome (WS) have poor drawing ability. Here, we investigated whether colour could be used as a facilitation cue during a drawing task.

METHOD

Participants with WS and non-verbal ability matched typically developing (TD) children were shown line figures presented on a 3 by 3 dot matrix, and asked to replicate the figures by drawing on an empty dot matrix. The dots of the matrix were either all black (control condition), or nine different coloured dots (colour condition). In a third condition, which also used coloured dots, participants were additionally asked to verbalise the colours of the dots prior to replicating the line drawings (colour-verbal condition).

RESULTS

Performance was stronger in both WS and TD groups on the two coloured conditions, compared with the control condition. However, the facilitation effect of colour was significantly weaker in the WS group than in the TD group. Replication of oblique line segments was less successful than replication of non-oblique line segments for both groups; this effect was reduced by colour facilitation in the TD group only. Verbalising the colours had no additional impact on performance in either group.

CONCLUSION

We suggest that colour acted as a cue to individuate the dots, thus enabling participants to better ascertain the spatial relationships between the parts of each figure, to determine the start and end points of component lines, and to determine the correspondence between the model and their replication. The reduced facilitation in the WS group is discussed in relation to the effect of oblique versus non-oblique lines, the use of atypical drawing strategies, and reduced attention to the model when drawing the replication.

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.

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.

Drawing the line: drawing and construction strategies for simple and complex figures in Williams syndrome and typical development

In the typical population, a series of drawing strategies have been outlined, which progressively emerge during childhood. Individuals with Williams syndrome (WS), a rare genetic disorder, produce drawings that lack cohesion, yet drawing strategies in this group have hitherto not been investigated. In this study, WS and typically developing (TD) groups drew and constructed (from pre-drawn lines and shapes) a series of intersecting and embedded figures. Participants with WS made use of the same strategies as the TD group for simple intersecting figures, though were less likely to use a typical strategy for more complex figures that contained many spatial relations. When replicating embedded shapes, the WS group used typical drawing strategies less frequently than the TD group, despite attempting to initiate a strategy that is observed in TD children. Results suggested that individuals with WS show a particular difficulty with replicating figures that include multiple spatial relations. The impact of figure complexity and task demands on performance are discussed.