Chromatic Signals in the Visual Pathway of the Domestic Cat

Abstract

Recordings from the cornea (ERG) and optic nerve (ONR) in the arterially perfused cat eye as well as in vivo from the visual cortex (VECP) revealed a rod (500 nm) mechanism and two clearly distinct cone mechanisms with sensitivity maxima near 460 and 560 nm, when strong selective chromatic adaptation was applied. However, the action spectra obtained during the first seconds of dark adaptation had a sensitivity maximum near 510 nm and came spectrally close to a rod action spectrum. It became apparent that a 510 nm mechanism was present during strong purple adaptation light, when rods were clearly saturated. This mechanism was able to follow flicker as high as 38 c/s; it could be found in the cone dominated VECP recordings; in the ERG it produced cone-like responses of short latency with pronounced a-waves and off-responses; it showed steep V-log I functions, different from rods, and followed the cone branch of the dark adaptation curve. Its spectrum could not be matched by any weighted addition of a 460 nm and 560 nm pigment nomogram. Apparently in cat under photopic conditions, besides a 460 and a 560 nm cone mechanism, a 510 nm mechanism is active which differs in many respects from rods. When strong white or yellow adapting lights are used, opponent-like interactions between these three mechanisms can be demonstrated.