Perceptual Coherence : Hearing and Seeing

230 Perceptual Coherence
Figure 5.15. The addition of a constant sinusoidal wave (i.e., the pedestal) provides
a way to determine if motion perception is due to motion energy detection.
From “Three-Systems Theory of Human Visual Motion Perception: Review and
Update,” by Z.-L. Lu and G. Sperling, 2001, Journal of the Optical Society of
America, A, 18, 2331–2370. Copyright 2001 by the Optical Society of America.
Reprinted with permission.
motion of a moving luminance or contrast grating. The dark and light
bands of the grating oscillate back and forth, and this effect is purely due to
the addition of the pedestal energy (figure 5.15).
First, if the detection systems for first-order or second-order patterns are
based on energy detection, then the addition of the pedestal should have no
effect on the perception of motion, because a static wave does not change
the output. A moving luminance grating will appear to move to the right
even if the pedestal is added. (This outcome does not tell us if there are one
or two systems; it simply tells us if the systems can detect energy.)
Second, if the detection systems for first-order or second-order patterns
are based on the detection of features such as light or dark peaks, zero
crossings, or valleys, then the addition of the pedestal should result in the