Tangent fields from population coding

Abstract

This paper addresses the problem of local orientation selection or tangent field estimation using population coding. We use Gabor filters to model the response of orientation sensitive units in a cortical hypercolumn. Adopting the biological concept of population vector decoding [4], we extract a continuous orientation estimate from the discrete set of responses in the Gabor filter bank which is achieved by performing vectorial combination of the broadly orientation-tuned filter outputs. This yields a population vector the direction of which gives a precise and robust estimate of the local contour orientation. We investigate the accuracy and noise robustness of orientation measurement and contour detection and show how the certainty of the estimated orientation is related to the shape of the response profile of the filter bank. Comparison with some alternative methods of orientation estimation reveals that the tangent fields resulting from our population coding technique provide a more perceptually meaningful representation of contour direction and shading flow.