Perception of Edges Versus Areas by the Crab Carcinus

Abstract

1. In the previous paper it was shown how a crab remembers the former position of a drum which has been moved in the dark. The technique can be used to test what aspects of the visual field the crab has seen. 2. If the crab sees stripes as black and white areas, the responses with increasing drum movement will repeat themselves at each stripe period, but if only edges are seen the responses pass through two periods for each stripe period of drum movement. 3. With the seeing eye clamped and the moving eye painted over, a controlled amount of tremor can be imposed on the seeing eye by oscillation of the drum. 4. The perception of edges, as opposed to areas, of black and white stripes is enhanced by artificially imposed tremor. 5. Under closed-loop conditions, with movable seeing eyes, some crabs behave as if they perceive enhanced edges.