Field adaptation causes proportional changes in cone response latency and log sensitivity for (1) psychophysical reaction times to threshold stimuli, (2) intracellular recordings of turtle cone responses, (3) local electroretinogram recordings of monkey cone responses and (4) theoretical impulse response functions derived from psychophysical flicker thresholds. To a good approximation, this relationship holds for all levels of cone adaptation except those that cause significant photopigment bleaching. For L and M cones, the proportionality constant between latency and log sensitivity appears to be cone-specific and largely independent of spatiotemporal stimulus parameters. For S cones, the proportionality constant depends to some extent on influences from other cone types.