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Marie de Montalembert, Laurent Auclair, Pascal Mamassian; Where is the sun for hemi-neglect patients?. Journal of Vision 2008;8(6):443. doi: https://doi.org/10.1167/8.6.443.
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The visual system uses prior constraints to disambiguate a scene, in particular that the light source position is preferentially assumed to be comming slightly from the left rather than straight above (Sun and Perona, 1998, Nature Neuroscience, 1, 183–184). One explanation of this bias could be a cerebral hemispheric difference. This hypothesis makes an interesting prediction: hemi-neglect patients might use a default light source position at a location different from the one found for normal observers. The aim of this study was to explore in neglect patients their preferred light source position. For this purpose we used the ambiguous shaded “Polo Mint” stimulus (Gerardin, de Montalembert and Mamassian, 2007, Journal of Vision, 7, 1–11), a ring divided in eight equal sectors. All but one sectors had the same shape, convex or concave, as determined by the light source position. Participants had to report the side (left or right) of the odd sector, and in a second task, to report the shape (convex or concave) of this odd sector. Five neglect patients and fourteen control participants ran the experiment; patients presented a neglect syndrom after a right temporo-parietal lesion due to a stroke or a tumor; they did not present any visual deficits such as hemianopsia or other visual field deficit. Results show a significant reduction of the light source position bias for neglect patients, but they do not present a right bias. This left bias could be explained by an attentional bias on a representation. Such an explanation is consistent with recent theories on mechanisms underlying the neglect syndrome.
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