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1 Introduction We describe a new illusion of visual motion, which we have named after Mondrian's

Summary: 1 Introduction
We describe a new illusion of visual motion, which we have named after Mondrian's
well known painting Broadway Boogie-Woogie. This painting contains checkered strips
which appear to shift around during inspection in a jazzy, unstable way. Our figure 1
contains a grid of similar lines, composed of alternating light and dark squares.
If the whole pattern is moved obliquely up to the right at 1 deg sĄ1
to 10 deg sĄ1
the eyes fixate a stationary point (or if the eyes track an obliquely moving finger, which
comes to much the same thing), a curious illusion can be seen. The small squares within
each line appear to flow or race along the lines. The speeded flow `overtakes' the
motion of the lines themselves, so that, if the pattern moves up to the right, the small
squares seem to race up the verticals and to the right along the horizontals. Moreover,
the vertical and horizontal lines look as though they are not rigidly welded together,
but instead are sliding over each other (see Anstis 1990). An animated version of the
illusion can be viewed on our web page at http://www-psy.ucsd.edu/$sanstis/SATric.html
and the Perception website: http://www.perceptionweb.com/misc/p3378/. We show that the
illusion is greatest when the background luminance matches the average luminance
of the light and dark squares. When the background is substantially darker (or lighter)
than the mean luminance of the squares, the illusion vanishes (see right side of figure 1)


Source: Anstis, Stuart - Department of Psychology, University of California at San Diego
Cavanagh, Patrick - Department of Psychology, Harvard University


Collections: Biology and Medicine