Dark adaptation and the Pulfrich effect

Abstract

RESULTSThe Pulfrich effect here is measured as the difference in position of the pointer M under experimental conditions from its settings made under control condition 1. In Fig. I Procedure Each S was given several hours of practice in viewing the Pulfrich effect before he was tested. At the start of each experimenta. session S viewed the stimuli through the artificial pupils for 10 min to achieve a steady pre-experimental level of light adaptation. Then, at time 0, a neutral density filter was dropped into place in front of S's left eye and he instantly adjusted the pointer M so that it appeared equidistant with the nearest point of the phenomenal path of the moving pointer P. If the initial setting could not be made within 2 or 3 sec to S's satisfaction, the filter was removed and the procedure repeated. The S then viewed the moving pointer P for 20 min, keeping the adjustable pointer M adjusted to the same apparent distance. Fixation was maintained on the pointer P. The position of M was recorded for the initial setting and at 1 min intervals thereafter.For each of the two Ss used, 10 values of neutral density filter were employed, from 0.3 to 3.0 log units in steps of 0.3. Each value was used for 10 experimental sessions, the successive treatments for each S being arranged in a 10 by 10 Latin square. About 60 h of testing were required for each S.Control readings were obtained under two conditions. In the first (control condition 1), settings of M for apparent equidistance with P were made under conditions identical to an experimental session, except that no filters were employed, to test for stability of depth judgments over time. In control condition 2, S was given a 2D-min preadaptation period using one of the filters (during which he viewed the stimuli, but with P stationary) followed immediately by a 2D-min experimental session using that filter, during which readings were taken of the magnitude of the Pulfrich effect. This procedure was repeated for each filter value, to check that the magnitude of the Pulfrich effect had reached a true asymptote during the preadaptation period, and that S's settings of M thereafter were stable. ApparatusThe S viewed a moving pointer P, which was mounted on a turntable and crossed his line of sight from right to left every 1.8 sec, at a distance of 140 em. P moved at 31.4 em/sec. Between Sand P a half-silvered mirror was mounted at 45 deg, so that when his head was placed in an adjustable headrest P was visible through the mirror. A movable pointer M was mounted so that its reflected image in the mirror lay just below the level of P; by moving M along a scale perpendicular to his line of sight, S could make its reflected image appear equidistant with P.The S viewed the stimuli through 4-mm artificial pupils, to limit any effects due to change in pupil size and reduce the entry of extraneous stray light to the eyes. The pointers P and M were narrow upright cylinders, 2 em high, 3 mm wide, painted white and illuminated to provide luminances of 120 mL and 46 mL, respec...

Bloch’s law and a temporal integration model for simple reaction time to light

“…Since different stimulus intensities were used in each of the three experiments, the effective dark adaptation level was greatest in E 3, next greatest in E 2, and least in E 1. There is considerable evidence, both physiological (Levick & Zacks, 1970) and psychophysical (Standing, Dodwell, & Lang, 1968) showing that visual latency increases with the amount of dark adaptation, so that on this basis we would expect the longest "baseline" latency in E 3 and the shortest in E 1, which was found. If dark-adaptation level could somehow be held constant across all conditions, changes in T r from one condition to another could then be attributed to changes in the criterion, c. The lengthy procedure required, however, might be impractical in .…”

Bloch’s law and a Poisson counting model for simple reaction time to light

“…One possible explanation is that this latencydifference may be due to dark adaptation, since less adaptation was possible for higher intensity experiments due to trial-to-trial effects. Some evidence exists that visual latency increases with the amount of dark adaptation (Standing, Dodwell, & Lang, 1968). Another possibility is "expectancy": Since flashes are generally perceived later in the lower intensity experiments, the subject may expect to see them later, causing a delayed RT in those cases.…”

3d+2dtv

“…Subjects were instructed to respond only when they felt their eyes had adjusted, typically answering immediately for α R near 100% and waiting about a minute for α R near 0%. Partial adaptation to new light levels occurs immediately, with additional adaptation over approximately 20 minutes [Standing et al 1968]. We measured only the immediate effects; significant effects have previously been found when allowing subjects to adapt to differential light levels for as little as 1 minute [Aiba and Stevens 1964] or 3 minutes [Stevens and Stevens 1963;Dodwell et al 1968].…”