Perceptual Coherence : Hearing and Seeing

5
Perception of Motion
It is early August in Tennessee, and I am enjoying the flashing of
fireflies each evening. There are only a small number of fireflies,
and the flashes are unsynchronized. It is relatively easy to match the successive
flashes to each firefly. However, if there were many flies and their
flashes were synchronized so that there were alternate periods of dark and
light (as happens with several species), it would be very difficult to match
the sequence of flashes firefly by firefly. In the previous chapter, I considered
the correspondence problem for static textures. In this chapter, I consider
the correspondence problem for moving stimuli, primarily in the
visual domain, and tracking the erratic movements of fireflies is one of the
most difficult problems.
It could be argued that detecting motion is the most important thing animals
do. Animals must detect motion when they are stationary and when
they are moving. Motion degrades camouflage and crystallizes objects. It
protects us from predators and provides prey. At one level, motion perception
simply is another kind of texture segmentation. There is a change in the
visual field such that one region pops out and is perceived as beginning and
ending at different locations in the field. In fact, Julesz (1995) and others list
movement as one of the factors leading to texture segmentation. However, in
this section, I treat movement in terms of the correspondence problem to
emphasize the similarity to the perception of repetition and symmetry.
Two findings from the research on texture perception stand out for me.
The first is that both preattentive effortless perceiving and attentive “scrutinizing”
perceiving are found for visual textures and repeating noise segments.
It is not clear whether these two impressions imply that there are two
distinct and nonoverlapping processes or if it means that several processes
necessarily are active simultaneously, another example of multiresolution.
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