Receptor interactions and visual persistence.

Two experiments are described that provide evidence for an interaction between the cone and rod systems following the offset of a stimulus. Experiment 1 employs a visual persistence task in which the observer is required to integrate two brief flashes separated by a variable ISI. Threshold luminance as a function of ISI is determined for several conditions of target wavelength. Striking differences between short and long wavelength targets are found which indicate the possible exclusion of rod participation at the brief ISIs. Experiment 2 employs a forward-masking task to demonstrate that the stimulus conditions of the first experiment result in a transient reduction in rod system activity following stimulus offset while the cone system is still active. Results support this proposal. Implications for the locus of persistence within the visual system are discussed.