A response duration limiting effect in the frog's visual system.

Optic nerve axons were recorded in dark adapted frogs. The responses to light stimuli are dependent on 2 systems: a rate saturation- and a delayed quenching mechanism. In the rate saturation mechanism, an increase of stimulus intensity or diameter increases the firing rate of a unit, until a plateau is reached. In the delayed quenching mechanism the response duration decreases with increasing stimulus intensity or diameter. Interaction of these mechanisms causes the increase and decrease in the number of impulses with increasing stimulus intensity or stimulus diameter.