Comparison of frequency characteristics of photopic and scotopic S-potentials in the carp

Frequency characteristics of photopic and scotopic L-type S-potentials were studied in the carp retina, using either an impulse or a sinusoidal light input superimposed on a steady background light of various intensities. The photopic type responses were faster than the scotopic responses if their frequency characteristics were compared without background illumination. However, the difference was not absolute. Both types of responses became faster in the presence of background illumination. The stronger the background, the faster was the response. At relatively high background intensities, the response to a flash became diphasic due to the rebound effect which corresponds to a low frequency attenuation in the gain characteristics. The main difference between the two types of responses was found in the phase relation; the scotopic units showed more phase lag indicating an extra delay even under a condition in which the time course of their response was faster than that of the photopic units.