Bias in perception of ambiguous movement in discrete stimulus presentations

Goddard, Paul and Blackaby, L. and Wilson, Steve (2003) Bias in perception of ambiguous movement in discrete stimulus presentations. In: 26th European Conference on Visual Perception, 1st - 5th September 2003, Paris, France.

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Bias in perception of ambiguous movement in discrete stimulus presentations
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Official URL: http://www.perceptionweb.com/abstract.cgi?id=v0311...

Abstract

Successive presentations of two different stimulus configurations were used to generate a compelling but ambiguous apparent-motion sequence, such that the likelihood of the perceived motion being resolved as clockwise or anticlockwise was equal. In the first stimulus configuration, four small squares were arranged in a square formation (5 deg × 5 deg) about a central fixation mark; in the second, they were arranged in a diamond formation. Twelve naïve observers reported perceived direction of motion in discrete presentations (< 1 s), comprising three stimulus configurations (square - diamond - square; stimulus configuration duration 100 ms; ISI 200 ms). We were surprised to find that ten of the observers exhibited a strong bias for motion in one or other direction. This bias to report a particular direction persisted even when observers were informed of the inherent ambiguity of the stimulus. Next, in extended presentations (2 min) five observers indicated each occurrence of a perceived switch in direction. Despite individual variation, all observers reported switches in direction; an analysis of the interswitch durations conformed to a gamma distribution. These observations support the notion that uninterrupted presentations are required for perceptual switching to occur in ambiguous displays (Leopold et al, 2002 Nature Neuroscience 5 605 - 609).

Item Type:Conference or Workshop Item (Poster)
Additional Information:Successive presentations of two different stimulus configurations were used to generate a compelling but ambiguous apparent-motion sequence, such that the likelihood of the perceived motion being resolved as clockwise or anticlockwise was equal. In the first stimulus configuration, four small squares were arranged in a square formation (5 deg × 5 deg) about a central fixation mark; in the second, they were arranged in a diamond formation. Twelve naïve observers reported perceived direction of motion in discrete presentations (< 1 s), comprising three stimulus configurations (square - diamond - square; stimulus configuration duration 100 ms; ISI 200 ms). We were surprised to find that ten of the observers exhibited a strong bias for motion in one or other direction. This bias to report a particular direction persisted even when observers were informed of the inherent ambiguity of the stimulus. Next, in extended presentations (2 min) five observers indicated each occurrence of a perceived switch in direction. Despite individual variation, all observers reported switches in direction; an analysis of the interswitch durations conformed to a gamma distribution. These observations support the notion that uninterrupted presentations are required for perceptual switching to occur in ambiguous displays (Leopold et al, 2002 Nature Neuroscience 5 605 - 609).
Keywords:Bias, perception, vision, illusions
Subjects:C Biological Sciences > C800 Psychology
C Biological Sciences > C850 Cognitive Psychology
C Biological Sciences > C830 Experimental Psychology
Divisions:College of Social Science > School of Psychology
ID Code:3616
Deposited By: Alison Wilson
Deposited On:05 Nov 2010 14:16
Last Modified:13 Mar 2013 08:50

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