The perception of 3D form depends on hand conformation and the integration of stimuli of stimuli from the multiple points of contact with the hand. To understand the neural mechanisms underlying stereognosis we need to understand three things: 1) how neurons respond to surface structure at the individual points of contact, 2) how a stimuli at separate regions of skin are integrated, and 3) how this integration depends on hand conformation. The experiments proposed here are aimed at taking a first step towards understanding these three facets of 3D form perception.
Aim 1 is to determine how neurons in SI and SII cortex respond to 3D surface structure contacting a single finger. This study will be limited to surface curvature and edges of the kind that occurs when a finger contacts a rigid object. 3D surface structure varies in the plane parallel to and normal to the skin surface. The experiments related to aim 1 will study neural responses to edges and corners whose orientation and curvature vary in the plane parallel to the skin surface and neural responses to surface curvature normal to the skin surface.
Aim 2 is to determine how neurons in SI and SII cortex respond to stimuli presented to two fingers. Surfaces indenting tow finger tips signal different things about an object depending on the surfaces' relative motions, orientations, and curvatures. Experiments related to aim 2 will study 1) the effects of stimulus direction and velocity; b) the effects of edge orientation, and c) the effects of surface curvature and slope on adjacent fingers.
Aim 3 is to determine the neural mechanisms of objective constancy in the face of varying finger position. When we scan our fingers over an object the primary information from two or more fingers varies with finger spread but the percept is unaffected. The experimented related to Aim 3 concentrate on the convergent mechanisms (between proprioceptive and cutaneous information) that must operate to compensate for finger position when abduction varies.
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