Distinct position assignment mechanisms revealed by cross-order motion

Pavan, Andrea and Mather, George (2008) Distinct position assignment mechanisms revealed by cross-order motion. Vision Research, 48 (21). pp. 2260-2268. ISSN 0042-6989

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Abstract

Motion perception influences perceived position. It has been shown that first-order (luminance defined) motion shifts perceived position across a wide range of spatial and temporal frequencies. On the other hand, second-order (contrast defined) motion shifts perceived position over a narrow range of temporal frequencies, regardless of spatial frequency [Bressler, D. W., & Whitney, D. (2006). Second-order motion shifts perceived position. Vision Research, 46(6-7), 1120-1128]. These results suggest the presence of distinct position assignment mechanisms for first- and second-order motion. We investigated whether the first- and second-order systems independently encode and assign the position of a moving stimulus. To measure motion induced position shift we presented two horizontally offset Gabors placed above and below a central fixation point, with sine wave carriers drifting in opposite directions. Subjects judged the position of the top Gabor relative to the bottom one. We used both first-order Gabors (sinusoidal luminance modulation of a dynamic noise carrier enveloped by a static Gaussian) and second-order Gabors (sinusoidal contrast modulation of a dynamic noise carrier enveloped by a static Gaussian). Results showed a strong position shift in the direction of the carrier motion when both Gabors were first-order, a weak position shift when both Gabors were second-order, and no appreciable position shift when one Gabor was first-order and the other was second-order (cross-order motion). The absence of a position shift using cross-order motion supports the hypothesis that the two motion systems independently encode and assign the position of a moving object. These results are consistent with those of experiments investigating global spatial interactions between static first-order and second-order Gabor patches, indicating a commonality in the underlying spatial integration processes. © 2008 Elsevier Ltd. All rights reserved.

Item Type: Article
Schools and Departments: School of Psychology > Psychology
Depositing User: George Mather
Date Deposited: 06 Feb 2012 15:42
Last Modified: 14 Mar 2012 12:21
URI: http://sro.sussex.ac.uk/id/eprint/14048
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