No abstract

When mapped with white light, each receptive field consisted either of an excitatory ("on") center and a concentric inhibitory ("off") surround, or of the reverse arrangement. Monochromatic stimuli revealed that each receptive field was composed of two mutually antagonistic components (one excitatory, one inhibitory) which had different spectral sensitivities and different spatial distributions. For some units the two chromatic components had identical spatial distributions.

These units responded vigorously to stimuli moving entirely across their receptive field centers in one direction (preferred) and not at all when the direction of motion was reversed (null). The directional selectivity was the result of an inhibitory mechanism which prevented responses to null movements. Surrounding each field center was a concentric antagonistic region produced by a second inhibitory mechanism.