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Frank E. Visco, Scott B. Stevenson; The effect of edge polarity on the Pulfrich stereophenomenon. Journal of Vision 2006;6(6):627. doi: 10.1167/6.6.627.
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The Pulfrich stereo-phenomenon is a consequence of a difference in signal timing between the two eyes as a result of differing levels of retinal adaptation. Here we used moving edge stimuli to investigate the interaction between local light adaptation and luminance edges in generating these delays.
The “edge only” stimuli were moving sawtooth profiles with very shallow ramps, so that the luminance at a given point changed slowly (ramp) and then changed suddenly (edge) as the pattern moved across the CRT display. Depending on polarity and motion direction, the edge caused local luminance to increase from zero (leading edge) or to decrease from the top of the ramp (trailing edge). Each eye saw two ramps moving at 5 deg/sec in counterphase. Left and right eye images were fused with a mirror haploscope. Luminance differed between eyes by one log-unit to produce the Pulfrich phenomenon.
Subjects judged the relative depth of the edges as they passed one another at the center of the display and adjusted the stimulus timing to null any apparent depth. The delay required to null the depth quantified the Pulfrich phenomenon.
With 1 log unit of interocular luminance difference, leading edges produced a relative interocular delay of 17msec. Trailing edges produced a relative delay of 7msec.
The differences in timing between leading and trailing edges can be attributed in part to early multiplicative adaptation (Hayhoe etal. 1987), such that a trailing edge is subject to local adaptation whereas a leading edge is not.
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