Document Detail

A static geometrical illusion contributes largely to the footsteps illusion.
MedLine Citation:
PMID:  18686709     Owner:  NLM     Status:  MEDLINE    
When a black and a white rectangle drifts across a stationary striped background with constant velocity, the rectangles appear to alternately speed up and slow down. Anstis (2001, Perception 30 785-794; 2004, Vision Research 44 2171-2178) suggested that this 'footsteps' illusion is due to confusion between contrast and velocity signaling in the motion detectors of the human visual system. To test this explanation, three experiments were carried out. In experiment 1, the magnitudes of the footsteps illusion in dynamic and static conditions was compared. If motion detectors play an important role in causing the illusion, it should be reduced in the static condition. Remarkably, however, we found that the illusory misalignment between the black and the white rectangle was even more prominent in the static condition than in the dynamic condition. In experiment 2, we measured the temporal-frequency properties of the footsteps illusion. The results showed that the footsteps illusion was tuned to low temporal frequencies. This suggests that the static illusory misalignment can contribute sufficiently to the dynamic illusory misalignment. In experiment 3, the magnitude of the illusion was measured with the rectangles drifting on a temporally modulated background instead of a spatially modulated background. If contrast affects the apparent velocity of the rectangles, temporal modulation of a uniform background should also cause the footsteps illusion. However, the results showed that the magnitude of the illusion was much reduced in this condition. Taken together, the results indicate that the footsteps illusion can be regarded as a static geometrical illusion induced by the striped background and that motion detectors play a minor role at best.
Shoji Sunaga; Masayuki Sato; Natsuko Arikado; Hiroshi Jomoto
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Perception     Volume:  37     ISSN:  0301-0066     ISO Abbreviation:  Perception     Publication Date:  2008  
Date Detail:
Created Date:  2008-08-08     Completed Date:  2008-11-10     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0372307     Medline TA:  Perception     Country:  England    
Other Details:
Languages:  eng     Pagination:  902-14     Citation Subset:  IM    
Department of Visual Communication Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka 815-8540, Japan.
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MeSH Terms
Contrast Sensitivity / physiology*
Motion Perception / physiology*
Optical Illusions / physiology*
Photic Stimulation / methods*

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