Spatial Representations in the Parietal Cortex May Use Basis Functions

Abstract

The parietal cortex is thought to represent the egocentric posi(cid:173) tions of objects in particular coordinate systems. We propose an alternative approach to spatial perception of objects in the pari(cid:173) etal cortex from the perspective of sensorimotor transformations. The responses of single parietal neurons can be modeled as a gaus(cid:173) sian function of retinal position multiplied by a sigmoid function of eye position, which form a set of basis functions. We show here how these basis functions can be used to generate receptive fields in either retinotopic or head-centered coordinates by simple linear transformations. This raises the possibility that the parietal cortex does not attempt to compute the positions of objects in a partic(cid:173) ular frame of reference but instead computes a general purpose representation of the retinal location and eye position from which any transformation can be synthesized by direct projection. This representation predicts that hemineglect, a neurological syndrome produced by parietal lesions, should not be confined to egocentric coordinates, but should be observed in multiple frames of reference in single patients, a prediction supported by several experiments.