Temporal Summation of S-Cone Signals: Dependence of the Critical Duration on the Signal Polarity

Encoding luminance variations is essential for all next steps of information processing in the visual system. This process is divided between two channels, an ON channel excited by luminance increments and an OFF channel excited by luminance decrements. While the existence of an S-cone OFF channel is disputed (Calkins, 2001), there are psychophysical findings suggesting its presence (e.g., McLellan & Eskew, 2000).