Relative rod and cone contributions in iconic storage.

Abstract

Using a two-alternative forced-choice procedure, subjects were required to detect a 4’ spatial gap between two briefly presented luminous rectangles when there was a temporal delay between the offset of the first rectangle and the onset of the second. Since the rectangles were never on simultaneously, detection of the spatial gap must have involved short-term visual storage (STVS). For each condition (fixed ISI, wavelength, eccentricity), luminance was varied, and the 75% threshold for detecting the gap with STVS was estimated. The difference in the gap detection thresholds for the white and colored conditions were calculated and compared to the difference predicted from both the relative rod and cone densities of each colored filter. (This latter difference was determined experimentally with absolute and differential standard threshold procedures and was also calculated theoretically.) The results were that, for eccentricities of about 3°–10°, gap detection was done by the cones for ISIs up to roughly 100 msec but by rods for longer ISIs.