|The motion of contour discontinuities does not necessarily enter the
integration process. For instance, look at the dot painted on the line.
Relative to the circular aperture, the dot moves right to left. However,
this right-left motion fails to spread to the black contour, which moves
diagonally. Note, additionally, that the dot appears to slide on the contour,
as if the visual system analyzed the right-left motion into two components:
one orthogonal to the orientation of the line, and one parallel to it.
Thus the dot appears to move diagonally with the line, while at the same
time sliding along the line (Wallach,1935).
The sliding effect suggests that global segmentation processes also affect
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