Visual control of turning responses to tactile stimuli in the crayfishProcambarus clarkii

Summary Specimens of the crayfishProcambarus clarkii turn to face in the direction of a brief tactile stimulus delivered to a walking leg. The control system that guides this directed behavior was investigated under closed-loop and open-loop conditions. The accuracy of turns exhibited in these experiments was compared to baseline accuracy established by animals restrained from forward and backward walking but allowed to rotate in the yaw plane.Procambarus clarkii individuals deprived of visual feedback tended to undershoot the target angle. Response accuracy increased when a uniform field of stripes moved across the visual field in accordance with the turning movements of the animal. Response accuracy did not match the accuracy observed under baseline conditions, however, unless the responding animal encountered a novel visual image, such as the silhouette of a crayfish, in the moving visual field.Visual feedback thus influences the accuracy of turning in crayfish in two important ways. Movement of stripes across the visual field of a crayfish feeds back positively and promotes rapid turning during the initial phase of a response. This effect obtains regardless of the direction or rate of movement of the stripes in the visual field. The appearance of a novel image in the visual field feeds back negatively to inhibit at least partially further turning. Feedback from the visual system appears to fine tune basic turning movements initiated by a tactile stimulus and crudely directed according to that input. Turning behavior in the crayfish resembles in this respect compensatory eye movements in the lobster and escape responses in a number of arthropods.Neural mechanisms that may explain the experimental results are discussed with particular emphasis on the possibility of interaction between voluntary turning responses and optomotor reactions.