Orientation bandwidths of psychophysical channels in the human visual system were inferred from contrast thresholds for a special class of polar-separable, two-dimensional patterns. Detection thresholds for these patterns conformed to a model with linear filtering by orientation-selective channels followed by probability summation across these channels. The number of channels (6-8 pairs) and their half-bandwidths at half-sensitivity (approximately 17 degrees) did not differ at 4 and 10 cycles/degree. The results extend the many one-dimensional, linear system models of vision to two dimensions.