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Abstract

Humans can perceive object shape based on a range of different sources of visual information (or cues). Two cues to shape, that the visual system appears to be especially sensitive to, are horizontal binocular disparity and geometric perspective. This study examined the relationship between fMRI activity in the human brain and the perception of shape from perspective and disparity cues. Observers viewed open book stimuli consisting of a hinged plane receding symmetrically in depth. We parametrically varied the dihedral angle between the planes. Observers were required to judge which dihedral angle was larger (or more open) of two sequentially-presented stimuli. Stimuli were rear-projected inside a 3T scanner. Psychophysical judgments were made whilst fMRI responses were collected concurrently. We employed an event-related fMRI adaptation paradigm in which stimulus changes result in increased fMRI responses (rebound effect) compared with repeated presentation of the same stimuli. Psychophysical data were fit using Probit analysis and the perceptual discriminability of different stimuli was calculated. We examined fMRI responses in early retinotopic visual areas, higher object-related (Lateral Occipital Complex-LOC) and motion-related (hMT+/V5) areas. We observed significant fMRI rebound effects, that is increased responses compared with repeated presentation of the same stimulus, in early and higher visual areas. These rebound effects were consistent with the discriminability of the perceived shape in areas LOC hMT+/V5. These results suggest that both object and motion-related visual areas are involved in the perception of 3D shapes from multiple visual cues.