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Christopher R. L. Cantor, Clifton M. Schor; The flash-pulfrich effect. Journal of Vision 2005;5(8):204. doi: 10.1167/5.8.204.
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© ARVO (1962-2015); The Authors (2016-present)
The classical Pulfrich effect describes a perceived depth elicited by a moving object that is viewed with unequal illuminance in the two eyes. The image in the dimmer eye is thought to have a latency-induced spatio-temporal offset that results in a binocular disparity between the dim and bright images. The Pulfrich effect has a monocular correlate, the Hess effect, that describes the relative mislocalization of two moving objects of different brightness in the same eye. As would be expected, the dimmer object is seen to move with a positional lag.
We present a novel version of the Pulfrich effect based on another monocular mislocalization, the Flash Lag effect (FLE). The FLE describes the relative misalignment of two moving objects when they are presented for different temporal durations. The position of a flashed object appears to lag behind a continuously presented object. We developed a binocular correlate of this stimulus to produce a Pulfrich like motion-depth illusion.
We compared the Hess and FLE under monoptic and dichoptic conditions while varying luminance and flash duration. Both dichoptic conditions produced Pulfrich depth effects with pendular motion. The dichoptic Hess condition produced the classic Pulfrich effect. When we combined the Hess and FLE in the dichoptic condition, we could reverse the depth direction of the classic Pulfrich effect if the brighter image was flashed. Thus the dichoptic FLE produced disparities that were independent of those produced by luminance difference between the two eyes.
*Note that the flash-Pulfrich effect is not to be confused with the stroboscopic-Pulfrich effect (Lee 1970) that attempts to cancel binocular disparities by strobing both bright and dim images. The flashed-Pulfrich effect is generated by strobing only one of the images.
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