The optokinetic response (OKR) of rainbow trout was investigated using rotating vertical black and white stripes. The rainbow truot showed two kinds of OKR patterns, Sliding-OKR (S-OKR) and Circular-OKR (C-OKR). S-OKR means the response as the fish follows the rotating stripes like a hand of a clock, while C-OKR is the response as the fish follows the stripes along the inner wall of an experimental trough. The S-OKR appeared mainly when the stimulus velocity (the rotating velocity of the stripes) was low (20 deg/s), while the C-OKR was dominant when the stimulus velocity was high (more than 60 deg/sec). With the stimulus velocity within an appropriate range, the fish followed the simulus as fast as the stimulus itself.
The maximum followable velocity (Vmax) depended upon the stripe width and the illumination intensity, while the minimum followable velocity (Vmin) was not affected by these factors. An abnormal OKR (very rapid response to only one stimulus direction) was produced by unilateral eye-enucleation. The unilateral tectal-ablation had the same effect on the OKR as the contralateral eye-enucleation. These results suggest that visual input from both eyes in necessary for normal OKR and that most of these inputs project to the contralateral optic tectum.
