title: A haptic size-contrast illusion affects size perception but not grasping.
abstract: Object features (e.g. size, shape and orientation) are relevant for recognition and identification, but also for the control of manual actions. Converging evidence suggests a dissociation between the visual systems that mediate object perception and object-directed action. Here we present evidence suggesting that a similar dissociation might exist in the haptic domain. We demonstrate that a haptic variation of a size-contrast illusion influences the perceived size of a target object, but not the degree to which the hand is opened when that object is the target of a grasping movement. This finding is consistent with the view that object perception is "scene-based" and takes into consideration not only the size of the target object but also the sizes of other nearby objects. In contrast, the control of object-directed action is primarily driven by the absolute size of the target object independent of the relative sizes of other objects in the environment, suggesting a "actor-based" frame of reference. The present findings suggest that dissociations between action and perception are not unique to the visual system, but might instead reflect a general organizational principle of sensory processing.
authors.affiliation: School of Health and Human Performance, Dalhousie University, 6230 South Street, Halifax, Nova Scotia, B3H 3J5, Canada. David.Westwood@dal.ca
authors.forename: David A
authors.initials: DA
authors.lastname: Westwood
authors.forename: Melvyn A
authors.initials: MA
authors.lastname: Goodale
mesh_terms: D000328:Adult; D005260:Female; D006225:Hand / Q000502:physiology; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology*; D011601:Psychophysics; D013028:Space Perception / Q000502:physiology*