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Viewer-centered and body-centered frames of reference in direct visuomotor transformations.
M Carrozzo1, J McIntyre, M Zago
1Human Physiology Section, Scientific Institute Santa Lucia, via Ardeatina 306, I-00179 Rome, Italy. carrozzo@caspur.it
Experimental Brain Research
|December 11, 1999
Summary
Reaching movements use egocentric frames of reference. Sensorimotor transformation gradually shifts from viewer-centered to body-centered and arm-centered coordinates for accurate endpoint specification.
Area of Science:
- Neuroscience
- Cognitive Science
- Human Motor Control
Background:
- Previous research suggested reaching endpoint specification in an egocentric frame.
- Distinguishing sensorimotor transformation from short-term memory storage was challenging due to memorized targets.
Purpose of the Study:
- Investigate sensorimotor transformation directly.
- Examine reaching toward continuously visible targets, bypassing memory storage.
Main Methods:
- Utilized a virtual reality system for 3D target presentation.
- Employed two tasks: 'Seen Hand' (with visual feedback) and 'Unseen Hand' (without feedback).
Main Results:
- 'Seen Hand' task: variability and contraction axes converged toward the viewer's midpoint.
- 'Unseen Hand' task: contraction correlated with sight-line; variability axes rotated anti-clockwise, not viewer-centered.
- Findings support a two-stage transformation process.
Conclusions:
- Reaching endpoint specification involves a gradual coordinate transformation from viewer-centered to body-centered and arm-centered.
- Parietal areas integrate visual and proprioceptive signals for egocentric reaching representations.