CONE ROD INTERACTION OVER TIME AND SPACE

Scotopic background stimulation can elevate [human] photopic increment thresholds by > 2 log units. This cone-rod interaction is greatest on small backgrounds (< 1.degree. diameter), but is found consistently on large backgrounds as well. Interaction develops and disappears quickly as backgrounds are turned on or off, respectively. The onset, and in some cases the offset, of a background stimulus can produce an additional, transitory interaction that augments the interactions that is maintained by continued presentation of the same background. A simple center-surround model of cone-rod interaction is suggested: nearby scotopic excitation raises photopic thresholds and more distant scotopic stimulation primarily antagonizes this interaction.