The influence of visual pattern combinations on responses of movement sensitive cells in the cat's superior colliculus.

Summary This investigation was generally aimed at determining how the responses of movement sensitive cells in the cat's superior colliculus are influenced by the types, and the combinations, of light patterns used to stimulate the retina of one eye. In particular, it was of interest to see whether the responses of such cells are either enhanced, or diminished, when one pattern in the visual field is made to move at a given velocity relative to another, as compared to a single pattern moving at the same velocity. The responses of 41 single neurons in the superior colliculi of 18 unanesthetized, pre-trigeminal cats were recorded with extracellular microelectrodes. Eighteen units were tested for variations in directional selectivity and/or orientation preference , and 25 units for variations in velocity preference , when one moving pattern (or pattern combination) was substituted for another. Eleven units were tested for variations in excitability when movement of one pattern relative to another , at one given velocity, was substituted for the movement of a single pattern at the same velocity. (On some units more than one type of test was done.) Twenty-five units (61%) showed a change in at least one of their response characteristics (directional selectivity, orientation preference, velocity preference, excitability) when tested with different patterns or pattern combinations. It is suggested that these findings may be related, on a neural level, to human psychophysical data which suggest that the subjectively perceived velocity of an object moving in the visual field depends to a significant degree on the number, and the configuration, of moving and non-moving objects present.