Local-Global visual deficits in Williams Syndrome: Stimulus presence contributes to diminished performance on image-reproduction

Impainnents in visuospatial processing exhibited by individuals with Williams Syndrome (WS) have been ascribed to a local processing bias. The imprecise specification of this local bias hypothesis has led to contradictions between different accounts of the visuospatial deficits in WS. We present two experiments investigating visual processing of geometric Navon stimuli by children with WS. The first experiment examined image reproduction in a visuoconstruction task and the second experiment explored the effect of manipulating global salience on recognition of visual stimuli by varying the density of local elements possessed by the stimuli. In the visuoconstruction task, the children with WS did show a local bias with respect to controls, but only when the target being copied was present; when drawing from memory, subjects with WS produced a heterogeneous pattern of answers. In the recognition task, children with WS exhibited the same sensitivity to global figures as matched controls, confinning previous findings in which no local bias in perception was found in WS subjects. We propose that subjects with WS are unable to disengage their attention from local elements during the planning stage of image reproduction (a visual-conflict hypothesis).