Other Variations

In the past thirty years, modifications have been made to the Classical Pulfrich effect to 'eludicate neuronal mechanism for processing delay and disparity" ( Read & Cumming, 2005). The two more prominent modifications are the stroboscopic Pulfrich effect and the dynamic visual noise.

The stroboscopic Pulfrich effect

In the stroboscopic version of the Pulfrich effect, "a target is presented in apparent motion, jumping from one point to another point across the screen instead of moving continous, and is viewed with interocular delay" (Read & Cumming, 2005). Figure 5 shows the space/time diagram for the stroboscopic pulfrich effect. The dotted lines represent the trajectory of the moving objects while the "star" represent its brief appearance. It was found that " at any instant in time, the stimulus is visble to only one eye" (Read & Cumming, 2005). Therefore, there is no spatial disparity but there is temporal delay( the difference between the "stars", J) which causes the perception of depth to be present.

Figure 5. Space/Time diagram for the stroboscopic Pulfrich effect (Read & Cumming, 2005)

Dynamic visual noise

Dynamic visual noise "resembles the "snowstorm" on an untuned television" (Read & Cumming, 2005). When viewed with an interocular delay, "the noise appears to swirl in depth, with points in front of the screeen moving towards the delayed eyes, and points behind it in the opposite direction" (Read & Cumming, 2005). The dynamic visual noise is unlike the pulfrich effect, in that the depth perception experience is not merely a "trival consequences of stimulus geometry" (Read & Cumming,2005).

Thus, we see that the classical explanation of the classical pulfrich effect cannot account for the results experience by the Stroboscopic Pulfrich effect and the dynamic visual noise. In fact, in Lee’s 1970 paper, he explicitly said that the “classical explanation doesn’t seem to work for the Stroboscopic Pulfrich effect” (Lee, 1970).As a result, this gave birth to the joint encoding of motion and depth explanation.