Extending the ‘dorsal stream vulnerability hypothesis’: Spatial reorientation and motion and form coherence in children and adults with Williams syndrome

Abstract

INTRODUCTION. From results of our previous studies on motion and form coherence thresholds, and on a modification of the Goodale post box task, we have put forward a general hypothesis of ‘dorsal stream vulnerability’, where certain brain circuits, within the parietal and frontal lobes together with the cerebellum, develop differently to normal in Williams Syndrome (WS) children. Using comparative measures of motion and form coherence, we have extended this hypothesis to children with autism and focal lesions leading to hemiplegia and elucidated the brain networks using fMRI in normal adults.

METHODS. We have tested both high functioning adults and young children with WS. We report results on two tasks: (a) an adaptation of the ‘altered views’ task of spatial reorientation — a virtual reality game to assess hippocampal function (adapted from O′ Keefe, Burgess and King); (b) Form and motion coherence thresholds in WS adults.

RESULTS. In the altered views task, two inter-related difficulties have been identified for WS individuals: i) understanding the visual transformation from 2D to 3D; ii) the ability to switch between spatial representations at different positions in space (although spatial memory from a constant viewpoint may be normal). On coherence tasks we find that form coherence thresholds did not differ significantly between our groups of WS adults and normal controls, but motion coherence thresholds were significantly higher for the WS group.

DISCUSSION. The results suggest that poor dorsal stream functioning in WS continues into adulthood, and that it is coupled to a difficulty in transforming environmental spatial information which may require hippocampal processing of visuospatial information. We discuss the broader ‘dorsal stream hypothesis’ in relation to other neurodevelopmental disorders such as perinatal brain injury.