Contextual effects in speed perception may occur at an early stage of processing.
Baker, Daniel H. and Graf, Erich W. (2010) Contextual effects in speed perception may occur at an early stage of processing. Vision Research, 50, (2), 193-201. (doi:10.1016/j.visres.2009.11.011).
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How does nearby motion affect the perceived speed of a target region? When a central drifting Gabor patch is surrounded by translating noise, its speed can be misperceived over a fourfold range. Typically, when a surround moves in the same direction, perceived centre speed is reduced; for opposite-direction surrounds it increases. Measuring this illusion for a variety of surround properties reveals that the motion context effects are a saturating function of surround speed (Experiment I) and contrast (Experiment II). Our analyses indicate that the effects are consistent with a subtractive process, rather than with speed being averaged over area. In Experiment III we exploit known properties of the motion system to ask where these surround effects impact. Using 2D plaid stimuli, we find that surround-induced shifts in perceived speed of one plaid component produce substantial shifts in perceived plaid direction. This indicates that surrounds exert their influence early in processing, before pattern motion direction is computed. These findings relate to ongoing investigations of surround suppression for direction discrimination, and are consistent with single-cell findings of direction-tuned suppressive and facilitatory interactions in primary visual cortex (V1)
|Keywords:||speed perception, surround suppression, facilitation, plaid|
|Subjects:||Q Science > Q Science (General)
B Philosophy. Psychology. Religion > BF Psychology
|Divisions:||University Structure - Pre August 2011 > School of Psychology > Division of Cognition
|Date Deposited:||13 Jan 2010|
|Last Modified:||28 Mar 2014 15:16|
Exploring mechanisms for the resolution of ambiguity in visual scenes
Funded by: BBSRC (BB/E012698/1)
Led by: Erich William Graf
1 August 2007 to 31 July 2009
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