Abstract
Response characteristics of the previously categorized four types of cat retinal ganglion cells (ON-I, OFF-I, ON-II and OFF-II) were investigated using light and dark spot stimuli by recordings of unit discharges from the optic tract, and phasic and tonic nature of these four types of cells were further clarified. ON-I and OFF-I are phasic in nature and respond to only a transient increase and decrease in luminance, respectively. ON-II and OFF-II are tonic and continue to respond to a stationary light and dark contrast, respectively. Besides, a difference is also found between ON-I and ON-II in the firing patterns of the transient response to a bright spot stimulus. ON-I responds to the onset of a bright spot with an initial burst followed by dispersed discharges. In ON-II's transient response, initial discharge rate is as high as that of ON-I's burst, but in contrast with the case of ON-I's response, the discharge rate gradually decreases toward a mean rate of sustained responses to the spot.
