CHANGES IN CRITICAL DURATION DURING DARK-ADAPTATION

Critical duration was measured using a 10 min test spot, located 5° from the fovea, in the nasal visual field. Subjects (N = 2) were pre-adapted to a luminance of 2.3 L (23,000 td) for 10 min. Data were then collected at 250 and 500msec, 1, 2, 4, 7, and 10 sec of dark-adaptation. For each of these times, stimulus duration ranged from 9.5 to 152 msec and temporal summation capability was calculated from resulting threshold determinations. Within the first 10 sec of dark-adaptation, critical duration increased from 30 to 80 msec, with approx 75% of the change occurring within the first 2 sec for both observers. These results show that increases in temporal summation capability contribute to lowering of threshold primarily during the very early stages of dark-adaptation. © 1979.