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Claudia L. R. Gonzalez, Tzvi Ganel, Melvyn A. Goodale; Perceptual illusions affect visually-guided actions with the non-dominant but not with the dominant hand. Journal of Vision 2005;5(8):354. doi: 10.1167/5.8.354.
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The visuomotor system that controls real-time target-directed movements is remarkably resistant to a wide range of perceptual illusions. The fact that the visual control of action is refractory to visual illusions has been used as evidence to suggest that vision-for-action and vision-for-perception are functionally and neurally dissociable. Nevertheless, one might expect that more deliberate and less-practiced actions, which would involve more cognitive control, might be susceptible to perceptual illusions. To test this idea, we asked subjects to reach out and grasp simple objects with their non-dominant (left) hand and compared their performance to that of their dominant (right) hand in the context of two pictorial illusions. In Experiment 1, we found that even though grasping movements using the dominant hand were completely unaffected by the Ponzo illusion, the illusion had a significant effect on grasping movements with the non-dominant hand. In Experiment 2, we replicated these results using the Ebbinghaus illusion. In other words, in both experiments, grip aperture was scaled to the real size of the target when participants used their right hand but to the apparent (illusory) size of target when they used their left hand. This dissociation was accompanied by longer movement times, as well as by greater variability in movement trajectories in the left hand. These results indicate that qualitative differences exist between the visual control of actions that are performed by the dominant and non-dominant hands. The fact that actions with the right hand but not with the left are resistant to perceptual illusions may reflect a basic distinction in the neural substrates of the visual control of automatic and controlled movements. In addition, our findings suggest that one must be careful in the selection of actions when testing predictions about possible dissociations between vision-for-perception and vision-for-action.
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