Two-pulse measures of temporal integration in the fovea and peripheral retina.

Abstract

The temporal integration of luminous energy was compared in the fovea and at 7 ° eccentricity using a white-appearing stimulus provided by a glow modulator tube transilluminating a 21.8′ opal glass target in a free-viewing situation. In Experiment 1, a three-interval temporal forced-choice adaptive staircase procedure was used to estimate thresholds for brief (3-msec) and long (102-msec) two-pulse stimuli. The data of five observers showed that in the fovea the long stimulus required significantly more luminous energy at threshold than the brief stimulus [t(14) = 5.60, p < .01]; however, at 7°, threshold luminous energy was not significantly different for the brief and long stimulus. Thus, Bloch’s law held in the periphery but not in the fovea, and the critical duration was longer (> 102 msec) in the periphery than in the fovea (< 102 msec). In Experiment 2, the detectability of a brief (3 msec) and a long (102 msec) two-pulse stimulus, both equal in total luminous energy, was compared at the same two retinal locations using a yes-no signal-detection procedure. The data of three observers showed that in the fovea the detectability of the long stimulus was 30% less than that of the brief stimulus, whereas at 7° brief and long stimulus detectability was approximately the same. Thus, both experiments demonstrated a foveal-peripheral difference in two-pulse visual temporal integration, with the fovea evidencing less integration.