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Frank E. Visco, Scott B. Stevenson; Time course of local adaptation in the pulfrich phenomenon. Journal of Vision 2005;5(8):254. doi: 10.1167/5.8.254.
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The Pulfrich stereophenomenon is a perception of depth in moving targets resulting from time delays in one eye. We have shown previously that Pulfrich effects can result from localized changes in retinal adaptation caused by objects in the immediate surround of a target. In this study we will attempt to characterize the time course of local retinal adaptation by leading the target in one eye with a small bright spot of light.
Two counter-phased, computer generated luminous discs (50cd/m2 − 10′ arc) on a black background were presented to each eye in a haploscope. The discs moved in a saw tooth wave at 300′ per second with a 2-degree excursion. A smaller (50cd/m2 − 2′ arc) luminous flank either led or followed the disc in its trajectory. By adjusting the interocular phase delay of the two discs the subject nulled any perceived depth. This difference in phase, quantified in milliseconds, corresponds to the interocular difference in signal timings. To determine the time course of adaptation we measured the Pulfrich caused by flanks at several temporal gaps relative to the bob.
A leading flank in one eye produced a Pulfrich effect of 12 to 15 msec for targets that were otherwise equal in luminance. The effect occurred when the flank led the disc by 0 to 100 msec and was maximum at about 35 msec. A lagging flank had little or no effect for any time lag.
In this experiment we were able to exploit this timing-critical judgment to characterize the time course of local retinal adaptation. As a flank traverses the retina, it leaves a wake of local adaptation in its path. As the disc passes through this region of adaptation its transmission time is shortened, causing depth with motion. When the position of a disc corresponds to the peak of the adaptation wave the relative disparity between the two retinal signals is at its maximum.
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