|In this pattern, you see a sort of spotlight that rotates in a gray
field, sequentially revealing different parts of a black circle over a
white surround. This interpretation is not obvious: at the tips of the
lentil-shaped region there is information suggesting that the lentil is
in fact rotating. Metelli (1940)
was so impressed with this lack of potential motion that he called this
phenomenon "apparent rest". Apparent rest may be understood as a demonstration
of the role of occlusion on motion integration. Given that the tips of
the lentil are not treated as real contour terminators, but as accidental
terminators revealed by the spotlight, the visual system does not enter
their motion signals into the computation of the global motion percept.
For an alternative interpretation of apparent rest in terms of a homogeneity
principle, see Metelli (1965).
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