Comparing frontal and lateral viewing in the pigeon. II. Velocity thresholds for movement discrimination.

Pigeons have been described as poor movement detectors when tested in the frontal binocular field. Retinal organization and behaviour suggest that motion sensitivity may be better in the lateral field. Pigeons were trained to discriminate the direction of moving square gratings (0.3 cyc/deg) appearing briefly (250 msec) contingent upon pecking a key (behavioural fixation). Stimuli were presented at isoacuity distance (40 cm) 25 degrees below the beak for frontal and 80 degrees back from the beak for lateral viewing. The animal had to discriminate the direction of movement for decreasing angular velocities. Results show that lateral motion sensitivity in the pigeon is 3 times better than frontal motion sensitivity. The fovea centralis, looking laterally, seems to be adapted for motion detection and may play a special role in the recognition of moving predators.