October 2003
Volume 3, Issue 9
Free
Vision Sciences Society Annual Meeting Abstract  |   October 2003
Illusory positional shifts affect both perception and action
Author Affiliations
  • Anna Ma-Wyatt
    Department of Psychology, The University of Western Australia, Australia
  • Paul V McGraw
    Department of Optometry, University of Bradford, UK
Journal of Vision October 2003, Vol.3, 122. doi:10.1167/3.9.122
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      Anna Ma-Wyatt, Paul V McGraw; Illusory positional shifts affect both perception and action. Journal of Vision 2003;3(9):122. doi: 10.1167/3.9.122.

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Abstract

Purpose: It has been suggested that separate visual pathways exist for perception and action (e.g. Goodale and Milner, 1992). Much of the evidence for this notion is based on the fact that the visuomotor, or action system, is resistant to many visual illusions. However, many experiments showing a dissociation between perception and action required subjects to make a motor response which was more complex than the equivalent perceptual judgement. We investigated whether a simple motor response (ballistic pointing) was influenced by an illusory change in visual position. Methods: When a grating is drifted behind a stationary window, the window itself appears displaced in the direction of motion. We used this effect to create an illusory positional offset. Four identical patches, presented in a diamond formation, all drifted either up, down, to the left, or to the right. In the perceptual condition, subjects were asked to judge the position of a line relative to the intersection of the perceived position of the four patches. In the action condition, subjects were asked to point to the perceived intersection. Results: Subjects showed a positional bias in judging the perceived centre of the four-patch arrangement in the direction of motion. Measures of positional bias were similar in direction and magnitude in the pointing condition. Conclusions: For a simple positional judgement, it is possible to demonstrate similar absolute errors for both perception and action, suggesting that a dissociation between the two systems is not a general finding and may be partially due to task demands.

Ma-Wyatt, A., McGraw, P. V.(2003). Illusory positional shifts affect both perception and action [Abstract]. Journal of Vision, 3( 9): 122, 122a, http://journalofvision.org/3/9/122/, doi:10.1167/3.9.122. [CrossRef]
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