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The effect of illusory size on force production when grasping objects.
D A Westwood1, A Dubrowski, H Carnahan
1Department of Psychology, University of Waterloo, Ontario, Canada.
Experimental Brain Research
|January 13, 2001
Summary
Visual illusions impact some, but not all, aspects of grasping and object size perception. This study reveals complex interactions between visual perception and action systems during prehension.
Area of Science:
- Cognitive psychology
- Neuroscience
- Human motor control
Background:
- Milner and Goodale's theory proposes separate visuomotor and perceptual systems.
- Previous research suggests some actions are immune to visual illusions, while others are not.
Purpose of the Study:
- Investigate the impact of illusory object size on prehension kinematics and grasping dynamics.
- Examine how visual illusions affect perceptual size judgments when object mass is constant.
Main Methods:
- Participants performed prehension tasks with objects of constant mass but varying illusory sizes.
- Grip force, load force, and movement kinematics were recorded.
- Perceptual size judgments were collected.
Main Results:
- The Ponzo illusion affected perceptual size estimates but not all prehension movements.
- Peak grip aperture, grip force, and wrist acceleration were sensitive to veridical size, not illusory size.
- Movement time and wrist velocity showed illusory size effects.
- Peak load force was unaffected by veridical or illusory size.
Conclusions:
- Certain prehension components are immune to pictorial size illusions, while others are susceptible.
- Complex interactions between perceptual and visuomotor systems govern anticipatory grasp scaling.