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M. Castelo–Branco, M. Mendes, M.F. Silva, L. Simões, M. Jorge, J. Saraiva; Low and High–Level Perceptual Deficits in Williams Syndrome: Implications for Neurodevelopmental Models of Visual Function . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5652.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Williams Syndrome – WS is a neurodevelopmental disorder of genetic origin that has been used as a model to understand visual cognition, in particular visual dorsal stream functions. We have hypothesized that early magnocellular deficits may contribute to abnormal visual dorsal processing in WS. Additionally, we have asked whether motion integration deficits become more prominent in tasks that require cross–talk between dorsal and ventral visual streams. Methods: A group of six adolescents with the classical WS cognitive profile was tested with a psychophysical technique based on a frequency–doubling (FD) illusion to selectively assess early magnocellular M–y processing. A test battery was used to probe different aspects of global motion perception (speed and direction discrimination, and coherence thresholds for planar and spherical surfaces at different time windows). Results: We have found a significant involvement of low–level magnocellular representations in WS as assessed by the FD contrast sensitivity task. On the contrary, no global significant differences were observed between WS and the control group regarding standard global motion perceptual tasks. We did however find in all subjects deficits in a novel structure from motion coherence task, which required motion integration of objects with unpredictable axis of rotation. Conclusions: Our findings provide a new magnocellular mechanism for the origin of dorsal stream deficits in these patients, and gives a new framework to understand the contribution of this pathway to dorsal stream functions. They are also consistent with recently described genetic and neuroanatomic abnormalities in early visual areas. Finally, selective structure from motion coherence deficits support the proposal that there is a separate pathway in the dorsal stream that is involved in structure from motion processing.
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