EVIDENCE FOR HIGH-VELOCITY SMOOTH-PURSUIT IN THE TRAINED CAT

It is generally accepted that in cats smooth pursuit velocity of the e ye never exceeds a few degrees per second. This is in contrast with ob servations in primates, where smooth pursuit velocity can reach values as high as 100 degrees/s. Cats were trained to fixate and pursue spot s of light appearing on a translucent screen. Spots were moved in the horizontal and vertical planes at different constant velocities up to 80 degrees/s. Eye position was recorded with the scleral search coil t echnique. Naive cats did not pursue moving targets with high efficienc y. Smooth eye movement velocity saturated at 5 degrees/s. After a few days of training, smooth-pursuit eye velocity increased with target ve locity and saturated at 25 degrees/s on average. However, velocities t wice as high have been observed frequently. When the target was unexpe ctedly extinguished, smooth eye movement velocity dropped to values cl ose to 0 degrees/s in approximately 350 ms. After a short training per iod (usually 5 times the same target presentation), the eye continued to move smoothly until the target reappeared. These data suggest that smooth pursuit eye movements of the cat are qualitatively similar to t hose of primates, but reach lower velocities and are more variable in their characteristics.