Perceptual Coherence : Hearing and Seeing

Perception of Motion 205
(The two frames are alternated in exactly the same way as in the classic apparent
motion presentations.) Even though the two stimuli are presented
discretely, the perception is that the elongated rectangle appears to grow
out of the contiguous square (figure 5.4A) even if the extension is the
brightness of the opposite square (figure 5.4B). If the elongated rectangle
touches both squares, then the rectangle appears to grow out of both if
the squares are identical or grows out of the one with the same brightness if
the squares differ (figure 5.4C).
In the second type of configuration, two different rectangles are shown
in frame 1, and then a connected combination of the two shapes is shown
in frame 2. The perceived motion goes along the smoothest contours and
tends to parse the figures along concave contours (figure 5.4D). In the
third type of configuration, the first frame contains a small square and
an elongated vertical rectangle. In one variant, the second frame contains
an elongated horizontal rectangle that appears to go behind the original
vertical rectangle (figure 5.4E). The perception here is a smooth extension
of the original square into a horizontal rectangle that proceeds
behind the vertical rectangle. If the two frames alternate, the horizontal
rectangle appears to extend and contract. In the other variant, the second
view contains two horizontal rectangles that do not touch the vertical
rectangle (figure 5.4F). The perception here is quite different: the original
square seems to extend to the right but is not part of the right rectangle,
and the right rectangle flashes on and off. The parsing module guesses
that the right square represents a brand-new object because it does
not butt up against the vertical rectangle. It is not part of the apparent
motion of the original left square (a similar auditory outcome is presented
below).
Using the same type of stimuli, Holcombe (2003) demonstrated that the
sudden onset of a visual stimulus could be interpreted as a morphing motion,
as found by Tse et al. (1998) above, but it also could be interpreted
as the disappearance of a shape in the foreground. Several examples are
shown in figure 5.5. If we simply compare figures 5.5A, 5.5B, and 5.5C, in
5.5A only 27% of observers see the small gray square morph into the gray
rectangle, but in 5.5C nearly all observers perceive a morphing motion.
Figure 5.5A is consistent with the black rectangle disappearing, exposing
the hidden part of the gray rectangle, but that cannot occur in figure 5.5C.
Figure 5.5B is an intermediate case because the gray segment overlapping
the black rectangle provides an ambiguous cue to occlusion. Similarly, in
5.5D and 5.5E, the small textured rectangle could occlude a central segment
of the black-and-white gradient in 5.5D, but the texture background
in 5.5E makes occlusion unlikely.
Tse et al. (1998) and Holcombe (2003) argued, successfully in my opinion,
that these results blur any distinction between the parsing and matching