ONE-PULSE AND TWO-PULSE MEASURES OF VISUAL TEMPORAL INTEGRATION

Visual temporal integration was investigated using one-pulse and two-pulse stimuli. The one-pulse stimuli were rectangular light flashes varying in duration from 20 to 316 msec; the two-pulse stimuli were two successive 2-msec rectangular light flashes separated by dark intervals varying from 0.1 to 88 msec. The visual field, in the form of a disk subtending 22' visual angle, was viewed binocularly by dark adapted observers.;Two intersecting functions, each describing a relationship between threshold luminance and stimulus duration, were fitted to each day's results. With L as threshold luminance (in mL), E as relative threshold energy (in mL-msec), T as total stimulus duration (in msec), and C and K as constants, these two functions can be represented by L X T = C and L = K for the one-pulse thresholds, and E = C and E / T = K for the two-pulse thresholds. The intersection of these functions for each of the two types of stimuli was used to provide an intercept measure of critical duration. This intercept measure of critical duration was about 100 msec for the one-pulse thresholds and about 50 msec for the two-pulse thresholds, estimates that are in general agreement with prior research.;In Experiment 1, one-pulse critical duration and two-pulse critical duration, though different in magnitude, were significantly correlated across days for one of the two observers (O:GB, r (14) = .75, p .05). This result suggests that both measures were responsive to similar organismic (subject) variables which changed across days. Daily variations were obtained for both the intercept measure of critical duration and the range of durations displaying partial integration.;The relationship E / T = K (one of the functions fitted to the two-pulse thresholds) adequately described two-pulse partial integration when daily results were individually examined. This relationship was not as clearly observable when the daily thresholds were combined, i.e., when thresholds were averaged across sessions, The relationship E / T = K has been reported for two-pulse thresholds in the light-adapted fovea, but this apparently is the first study to identify this relationship in the dark-adapted fovea.;The Random Method of Limits procedure enabled fast and reliable threshold determinations for all durations during a single testing session. In Experiment 1, both one-pulse and two-pulse thresholds were determined (during separate sessions) on each of 16 days. In Experiment 2, one-pulse thresholds were obtained on 8 days, and two-pulse thresholds were obtained on 8 subsequent days. Additionally in Experiment 2, thresholds of a constant duration control stimulus were obtained throughout each session to determine that neither practice nor fatigue effects were confounding the data. Two observers participated in each of the two experiments.