Eye Movements of the Crab Leptograpsus Variegatus Elicited by Imposed Leg Movements

1. The horizontal component of eyestalk movements elicited by moving the legs of blinded crabs is described. 2. The animals' bodies were fixed to a stand and the legs were supported on either a sphere or platform and subjected to movement around the three major axes (yaw, pitch, and roll). Both sinusoidal and stepped movements of the legs were studied. 3. The effect of moving the legs on one side only, homolateral or contralateral to the eyestalk was also studied. 4. The eyestalk excursion elicited by sinusoidal leg excursion around the vertical axi9 (yaw) is a nearly linear function of the leg excursions over the range of 1-40 peak to peak at o-i Hz. The amplification of the system is about 0-4 when the animal's legs are supported on a ball, and o-8-i-o when the legs are supported on a platform. 5. The frequency response of the system to yaw is nearly flat for eye excursions of 16° peak to peak, over the range of o-oo5-o-i Hz. 6. The visual system has a powerful braking effect on the eye rotation, when this is generated by the imposed leg movements. 7. Eyestalk responses to yaw can be interpreted to be compensatory in that they stabilize the eyes in space in freely moving animals. 8. Eyestalk movements to pitch and roll are complex. In roll, their horizontal component indicates the presence of considerable rectification in the leg proprioceptor-eye system. 9. The functional significance of the eyestalk movements in the horizontal plane is discussed.