Kwabena A. Boahen, Andreas Andreou
The goal of perception is to extract invariant properties of the underly(cid:173) ing world. By computing contrast at edges, the retina reduces incident light intensities spanning twelve decades to a twentyfold variation. In one stroke, it solves the dynamic range problem and extracts relative reflec(cid:173) tivity, bringing us a step closer to the goal. We have built a contrast(cid:173) sensitive silicon retina that models all major synaptic interactions in the outer-plexiform layer of the vertebrate retina using current-mode CMOS circuits: namely, reciprocal synapses between cones and horizontal cells, which produce the antagonistic center/surround receptive field, and cone and horizontal cell gap junctions, which determine its size. The chip has 90 x 92 pixels on a 6.8 x 6.9mm die in 2/lm n-well technology and is fully functional.