In both biological and artificial pattern-recognition systems, the detection of oriented light-intensity edges is an important preprocessing step. We have constructed a silicon VLSI device containing an array of photoreceptors with additional hardware for computing center-surround (edge-enhanced) response as well as edge orientation at every point in the receptor lattice. Because computing the edge orientations in the array local to each photoreceptor would have made each pixel-computation unit too large (thereby reducing the resolution of the device), we devised a novel technique for computing the orientations outside of the array. All the transducers and computational elements are analog circuits made with a conventional CMOS process
