Neuronal responses in the visual cortex of awake cats to stationary and moving targets

SummaryOver 300 single units from the visual cortex (within and around the projection of the central area) were recorded from awake and non-paralyzed cats (chronic preparation). Spontaneous activity of 25% of the neurons was below 3/sec, that of 75% above 3/sec (mean 7.65 spikes/sec). Diffuse illumination had only little influence, but nearly all neurons responded to stimulation with some sort of visual contrast. This would be either an irregularly moved shadow on the screen with irregular boundaries (e. g. a hand with moving fingers), a dark stripe moving in a certain direction, stationary parallel gratings with a certain orientation, or saccadic eye movements across a checkerboard. Although some neurons responding to one stimulus type could also be responsive to other stimuli, the majority of units only responded to one stimulus type. The responses to stationary gratings (alternating parallel dark and bright stripes) and to moving dark stripes are described in detail. Responses to stationary gratings showed no adaptation. The orientation of the grating stripes was critical for each neuron, the optimal and minimal response orientation were separated by about 90°. For movement sensitive neurons, the direction of the movement was critical. Most neurons had only one, some had two preferred directions separated by 180°. No statistically significant predominance of certain orientation or direction preferences was found. The preferred target velocity of movement sensitive neurons was between 10 and 60°/sec, above 80–100°/sec only occasional or no responses could be elicited. Neurons which responded to saccadic eye movements (above 300°/sec) in the presence of a checker board, usually did not respond to slower target movements below 100°/sec.The results support the view that the visual system has different channels for the perception of moving and of stationary objects.