Interaction between rod and cone signals studied with temporal sine wave stimulation.

If a temporal stimulus is presented through the cones, the threshold for a rod stimulus may be influenced even if the cone stimulus remains subthreshold. We have used sinusoidal stimulation to study the process underlying this rod-cone interaction. A first-order model is proposed consisting of a single threshold mechanism preceded by linear summation of rod and cone signals with a pure latency difference. Two deviations from this model are described. First, occasional additivity failures appear; second, if the phase difference characteristic is corrected for latency, the remaining part cannot be explained in terms of the de Lange curves of the rod and cone systems.