email: yweiss at cs dot huji dot ac dot il
The ease by which we compute motion of objects in a scene is deceptive. Here are some demonstrations of the ambiguity of motion and our visual system's use of perceptual grouping in order to resolve this ambiguity.
Note: If you cannot see the embedded videos, you can download them using the links in the caption. They are Quicktime format and will play in any compatible player.
A narrow ellipse oscillating rigidly about its center appears
However, a fat ellipse undergoing the same
motion appears nonrigid
The apparent nonrigidity of a fat ellipse is not really a
"visual illusion". A rotating ellipse or a nonrigid pulsating
ellipse can cause the exact same stimulation on our retinas. In
the ellipse contour is always doing the same thing, only the markers'
The ellipse's motion can be influenced by features not
physically connected to the ellipse. In this sequence (quicktime 420k)
the ellipse is always doing the same thing, only the dots'
The ellipse's motion is not influenced by spurious
features. In this sequence (quicktime 407k)
our visual system parses the scene into two rigidly moving
objects, rather than one nonrigdly deforming one.
So what does this mean?
Our visual system integrates multiple
measurements in order to analyze the motions in a scene. It also makes
a decision which measurements to integrate and which to segment. We
have developed a computational model of motion integration that is
consistent with human observers' perception of these stimuli. The
model is consistent with a wide range of previously published
phenomena and is described
in this paper.
Perceptual Science Group Home Page