Interaction of the movements of the two eyecups in the crab Carcinus

Summary 1. The movements of the two eyecups of the crab, Carcinus, have been recorded simultaneously during optokinetic responses. 2. Experiments in which the eyes view different visual stimuli reveal that, at the start of a response, the eyecups have a considerable degree of independence and can even move in opposite directions. As the response progresses, interaction between the eyes increases, until the eyecups move at similar velocities in the direction of the slower of the two visual inputs, or are stationary. 3. Similar interactions between the eyes were observed during memory responses and during the responses to sinusoidal oscillation of the two sets of stripes. Each eye has its own system for converting perceived motion into eyecup movement. These two systems are linked on the afferent rather than the efferent side of the brain. 5. The fast phase of optokinetic nystagmus is governed by the eye whose fast-phase movement occurs away from the midline, and the fast phases of this eyecup lead the other by 30-80 msec. Also, fast phases only occur at their normal frequency when the governing eye can see the stripes