Summary: 2003 Special issue
Moving objects appear to slow down at low contrasts
Department of Psychology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0109, USA
Moving cars give the illusion of slowing down in foggy conditions, because low contrast reduces perceived speed. A grey square that drifts
horizontally across a surround of black and white vertical stripes appears to stop and start as it crosses each stripe, because its contrast keeps
changing. A moving square whose vertical and horizontal edges have different contrasts will show illusory distortions in perceived direction.
Contrast also affects the apparent amplitude and salience of back-and-forth apparent motion. Finally, a line of black and white dots on a grey
surround moves in illusory directions, because of a mismatch in the contrasts along and across the dotted line. Thus, motion signals in the
early parts of the visual system are profoundly altered by stimulus luminance and contrast. This suggests that motion is coded by the relative
firing rates of neural channels tuned to fast and slow motion, with contrast-dependence being a motion analog of the BezoldBrucke hue
q 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Contrasts; Luminance; Motion perception; Speed perception
Motion perception allows us to keep track not only of
moving objects, but also of our own movements through
space (Gibson, 1950; Nakayama, 1985). It also provides
valuable raw material for neural modelers. One might guess