Advanced Search

Browse by Discipline

Scientific Societies

E-print Alerts

Add E-prints

E-print Network

  Advanced Search  

1 Introduction An object's motion cannot be determined from a single measurement on its contour

Summary: 1 Introduction
An object's motion cannot be determined from a single measurement on its contour
owing to the ambiguity known as the aperture problem (Wallach 1935; Marr and Ullman
1981; Adelson and Movshon 1982). Local measurements must therefore be combined
across space. In figure 1a, the ambiguous motion of the contour labeled 1 can be resolved
by combining it with another contour's motion, eg by intersection of constraints. Alter-
natively, one may utilize the unambiguous motion of a `feature,' such as the corner
labeled 2. It has long been recognized that unambiguous features can have powerful
effects on motion perception (Wallach 1935; Nakayama and Silverman 1988). However,
some features are spurious, such as the T-junction labeled 3 which is due to occlusion
(Shimojo et al 1989). The cross-bar of the T is a contour that is `owned' by the occlud-
ing region; the stem of the T is a contour that is occluded by that region. The stem
and cross-bar lie in different planes and the T-junction in the image is artifactual,
corresponding to no physical feature, and moving with no physical object. In the
example of figure 1, the two squares translate to the left and right but the T-junction
moves downward. Such spurious motions will distort motion estimates if they are treated
as real. Occlusions and the spurious motions that occur with them are common in
natural motion sequences, but humans generally discount them correctly. In the local
motion domain, however, spurious features are not obviously distinguishable from non-
spurious; form information is apparently needed and used in human motion interpreta-


Source: Adelson, Edward - Computer Science and Artificial Intelligence Laboratory, Department of Brain and Cognitive Science, Massachusetts Institute of Technology (MIT)


Collections: Biology and Medicine