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Distortion in perceived image size accompanies flash lag in depth
Terence C P Lee1, Sieu K Khuu, Wang Li
1Department of Psychology, The University of Hong Kong, Hong Kong SAR, China. terencel@hkbu.edu.hk
Journal of Vision
|October 4, 2008
Summary
The flash-lag-in-depth effect causes illusory changes in perceived object size. This size misperception is linked to stereomotion, not looming, suggesting novel depth perception mechanisms.
Area of Science:
- Visual perception
- Depth perception
- Illusory phenomena
Background:
- The flash-lag effect is a spatiotemporal visual illusion.
- Previous research focused on the flash-lag effect as a spatial offset.
Purpose of the Study:
- Investigate the flash-lag-in-depth effect.
- Examine accompanying illusory changes in perceived object size.
- Determine the role of stereomotion versus looming in this effect.
Main Methods:
- Used a dot-defined square moving in depth (stereomotion) and a flashed Gaussian blob.
- Observers matched the apparent size of the flashed blob against a reference.
- Manipulated square's motion (approaching/receding) and depth cue (stereomotion/looming).
Main Results:
- A strong flash-lag-in-depth effect was observed.
- Approaching motion reduced perceived flashed blob size; receding motion enlarged it.
- This size effect was diminished/eliminated when looming cues were used instead of stereomotion.
Conclusions:
- The flash-lag-in-depth effect is associated with illusory size changes.
- Stereomotion, not looming, drives this size misperception.
- Findings challenge simple projective geometry explanations for visual depth perception.
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