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Abstract:
Neurons with aligned visual and tactile receptive fields have
been reported in several interconnected regions of the parietal
cortex (VIP and area 7b), basal ganglia (putamen), and frontal
cortex (premotor area 6). In the premotor cortex, some bimodal
cells continue to respond to a visual object in the receptive field
even after the light is turned off, which suggests that the neural
system underlying these responses is bistable. A computational
model that can account for this phenomenon is presented based on a
recurrent network with a bistable shiftable attractor. The model
encodes object location close to the body by a self-sustaining
packet of activity on the somatotopic map.
Although sensory inputs from different modalities are dynamically
aligned on this map, the activity packet does not depend on these
inputs and can move continuously on the map using only motion
information. The map is also locally stable at a uniform low
activity state, corresponding to the absence of an object. The
model makes testable predictions for transient responses and what
happens when a second object is introduced. This model provides an
explicit, plausible sensorimotor mechanism for representing object
permanence in body-centered coordinates, and could be used to guide
motor behavior in the dark, behind occlusion, or when the target is
out of view.
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