The effect occurs because the filter reduces the luminance of the pendulum on the one retina, producing a slight delay in transmission to the binocular cells in the visual cortex. This delay means the pendulum’s dim image is “assumed” by the brain to lag behind spatially—as if noncorresponding points were stimulated—thereby fooling the brain into thinking the pendulum is moving in 3-D. The greater the velocity of the pendulum (for instance, during midflight), the greater the three-dimensionality experienced, hence its elliptical path in 3-D.
It has been a long journey from Leonardo, Wheatstone and Victorian parlor toys to modern physiology and psychophysics, but we have barely begun to understand the subtleties of binocular vision. In the next issue we will explore this theme further.
Note: This article was originally printed with the title, "Seeing in Stereo."
This article was originally published with the title Seeing in Stereo.