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J Neurophysiol (September 16, 2009). doi:10.1152/jn.00411.2009
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Submitted on May 13, 2009
Revised on September 3, 2009
Accepted on September 8, 2009

Radial biases in the processing of motion and motion-defined contours by human visual cortex

Colin W.G. Clifford1*, Damien John Mannion2, and James Scott McDonald2

1 The University of Sydney
2 University of Sydney

* To whom correspondence should be addressed. E-mail: colinc{at}psych.usyd.edu.au.

Luminance gratings reportedly produce a stronger fMRI BOLD signal in those parts of the retinotopic cortical maps where they are oriented radially to the point of fixation (Sasaki et al., 2006). We sought to extend this finding by examining anisotropies in the response of cortical areas V1-V3 to motion-defined contour stimuli. fMRI at 3T was used to measure the BOLD signal in the visual cortex of six human subjects. Stimuli were composed of strips of spatial white noise texture presented in an annular window. The texture in alternate strips moved in opposite directions (left-right or up-down). The strips themselves were static and tilted 45° left or right from vertical. Comparison with maps of the visual field obtained from phase-encoded retinotopic analysis revealed systematic patterns of radial bias. For motion, a stronger response to horizontal was evident within V1 and along the borders between V2 and V3. For orientation, the response to leftward tilted contours was greater in left dorsal and right ventral V1-V3. Radial bias for the orientation of motion-defined contours analogous to that reported previously for luminance gratings could reflect cue-invariant processing or the operation of distinct mechanisms subject to similar anisotropies in orientation tuning. Radial bias for motion might be related to the phenomenon of "motion streaks" whereby temporal integration by the visual system introduces oriented blur along the axis of motion. We speculate that the observed forms of radial bias reflect a common underlying anisotropy in the representation of spatiotemporal image structure across the visual field.







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