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Melanie Palomares, Barbara Landau, Howard Egeth, James Hoffman; Collinear inhibition in Williams Syndrome?. Journal of Vision 2003;3(9):667. doi: 10.1167/3.9.667.
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Williams Syndrome (WS) is a rare genetic disorder with a distinct cognitive hallmark: relatively spared language and profoundly impaired visuospatial cognition. This profile is of interest because it suggests that genetic deficits might target specific cognitive systems, in this case, the system of spatial cognition. Most studies WS have used complex visuo-motor tasks such as drawing or block construction to evaluate their visuospatial abilities. Some have suggested that these deficits are not linked to “low-level” visual functions such as stereopsis and acuity (e.g. Atkinson et al, 1999). However, neuroanatomical studies show that V1 has decreased volume (Reiss et al, 2000) and has abnormal connectivity (Galaburda and Bellugi, 2000) in WS.
To explore the contribution of “low-level” visual functions in WS deficits, we measured threshold contrast for detecting a grating with and without collinear flankers. In normal adults, collinear flankers facilitate grating detection (Polat and Sagi, 1993), which is thought to be mediated by the long-range horizontal connections in V1. We found that WS participants (12–33 years old) have contrast thresholds for detecting an unflanked grating that is as good as normal adults, and better than normal 3- to 5-year old children. However, we found that WS were actually worse (i.e. inhibited) in the presence of collinear flankers regardless of their distance from the target (at 3 and 9 lambda), while normal children showed no significant effects of flankers, and normal adults showed facilitation. Normal detection thresholds in WS indicate that their the mechanism underlying their feature detection is intact, while the lack of collinear facilitation in WS suggests that visual tasks requiring spatial integration is impaired, perhaps reflecting abnormal V1 connectivity.
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