Why does Listing's plane rotate during vergence?

Recall the afterimage experiment. It showed to perceptual consequences of obeying Listing's law. A horizontal line (gray) had the orientations shown on the right relative to the horizontal meridian (yellow-green) of the eye (the after image).

When the eyes converge

  • the right eye is looking left
  • and the left eye is looking right

If the eyes continued to obey Listing's law while converged then, when the eyes looked up, the horizontal gray lines would have different orientations in the two eyes and would therefore be seen with torsional disparity.

Likewise when looking down you would perceive a torsional disparity but in the opposite direction.

Copyright © 1996 Tutis Vilis and Douglas Tweed
University of Western Ontario
London Ontario Canada
Updated October 28, 2005

Comments welcome. Email to tutis.vilis@schulich.uwo.ca