Attention-dependent representation of a size illusion in human V1
Author
Fang, F.
Boyacı, Hüseyin
Kersten, D.
Murray, S.O.
Date
2008Source Title
Current Biology
Print ISSN
0960-9822
Electronic ISSN
1879-0445
Publisher
Cell Press
Volume
18
Issue
21
Pages
1707 - 1712
Language
English
Type
ArticleItem Usage Stats
139
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126
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Abstract
One of the most fundamental properties of human primary visual cortex (V1) is its retinotopic organization, which makes it an ideal candidate for encoding spatial properties, such as size, of objects. However, three-dimensional (3D) contextual information can lead to size illusions that are reflected in the spatial pattern of activity in V1 [1]. A critical question is how complex 3D contextual information can influence spatial activity patterns in V1. Here, we assessed whether changes in the spatial distribution of activity in V1 depend on the focus of attention, which would be suggestive of feedback of 3D contextual information from higher visual areas. We presented two 3D rings at close and far apparent depths in a 3D scene. When subjects fixated its center, the far ring appeared to be larger and occupy a more eccentric portion of the visual field, relative to the close ring. Using functional magnetic resonance imaging, we found that the spatial distribution of V1 activity induced by the far ring was also shifted toward a more eccentric representation of the visual field, whereas that induced by the close ring was shifted toward the foveal representation, consistent with their perceptual appearances. This effect was significantly reduced when the focus of spatial attention was narrowed with a demanding central fixation task. We reason that focusing attention on the fixation task resulted in reduced activity in-and therefore reduced feedback from-higher visual areas that process the 3D depth cues.