Perceived spatial displacement of motion-defined contours in peripheral vision

Zhao Fan & John Harris*
University of Reading, UK

Correspondence address: John Harris, School of Psychology and Clinical Language Sciences, University of Reading, Reading, UK, RG6 6AL. Email address: j.p.harris@reading.ac.uk

Abstract

 

Two types of motion-induced displacement of equiluminous kinetic contours were investigated. In line with Ramachandran and Anstis’ finding (1990), the direction of the first type was the same as that of unidirectional drifting dots next to static pattern. The kinetic contour in the second type of displacement was defined by two patterns moving in opposite directions, with the displacement in the direction of motion of the dots in the more eccentric field, so that the location of a kinetic contour defined by an expanding pattern is perceived as more eccentric, and that defined by a contracting as less eccentric. Two explanations for this effect (that the displacement reflects a greater weight given to the more eccentric motion, or that the region containing centripetal motion expands perceptually into that containing centrifugal motion) were tested in a further experiment by varying the velocity of the more eccentric region. The results ruled out explanations which are purely based on ‘special role of motion signals within the more eccentric field’. Instead, a mechanism based on processing imbalance between motion signals of different directions must be introduced in order to account for the perceived spatial displacement of the second type of motion-defined contours. Further control experiment showed that the difference in perceived location was not due to differences in the discriminability of expanding and contracting patterns. Our finding provides new evidence for a bias towards centripetal motion in human vision (Raymond, 1994), and suggests that the direction of motion induced displacement of kinetic contour is not always in the direction of an adjacent moving pattern. (Fan & Harris, 2008, Vision Research).

Demonstration 1: Perceived position displacement of equiluminous kinetic edges defined by unidirectional moving pattern and static texture

Demonstration 2: Perceived position displacement of kinetic edges defined by motion contrast: A new type of perceived spatial displacement

Demonstration 3: No perceived edge displacement was observerd - a ‘zero eccentricity’ condition

Demonstration 4: Perceived displacement of motion-defined edges in the ‘speed imbalance of expansion’ condition: the role of motion signals within the far half-pattern

Demonstration 5: Perceived displacement of motion-defined edges in the ‘speed imbalance of contraction’ condition: the addition of the 'speed imbalance' and 'centripetal bias'