Control of the prey orienting behavior depending on moving distance of the prey before initiation of turn in Rana catesbeiana

In our previous histological experiment, we have suggested that the optic tectum of the frog has some functional units with different sizes, and each one corresponds to output resolution of specific orienting behavior. In this study, therefore, we examined functional organization of prey orienting behavior in detail. Based on our model of orienting turn for prey, we measured turn angle of a frog (θ1), angle of a cricket before orientation response of the frog (θ2), error in orientation (θ1 minus θ2), amount of time for orienting, and angular velocity of orienting behavior from frame-by-frame analysis. Additionally, we examined moving pattern of crickets before orienting turn. The orienting responses were classified into three types Pattern A, B, and C in ascending order based on the moving distance. We plotted angular velocity of frog's orienting turn against θ1. The angular velocity showed a step-by-step increment. We also found that in only pattern A, where the crickets move the longest distance, the turn velocities are distributed discontinuously. The amplitudes where the distribution was mainly recognized showed good agreement with those where the step-by-step increment of turn velocity is observed. It is difficult for the frog to predict position of the cricket which is moving a long distance. Therefore, for such a target, they may turn into the nearest predetermined position to save energy.