Distinct position assignment mechanisms revealed by cross-order motion

Paven, A. 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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Distinct position assignment mechanisms revealed by cross-order motion
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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.

Item Type:Article
Additional Information: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.
Keywords:Position assignment, Motion-induced position shift, First-order motion, Second-order motion, Cross-order motion
Subjects:C Biological Sciences > C800 Psychology
C Biological Sciences > C850 Cognitive Psychology
Divisions:College of Social Science > School of Psychology
ID Code:4743
Deposited By: Alison Wilson
Deposited On:13 Oct 2011 18:17
Last Modified:13 Mar 2013 09:02

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