Binocular perceived direction

R. van Ee, M.S. Banks & B.T. Backus (1999). Perceived visual direction near an occluder. Vision Research, 39, 4085-4097. pdf
direct demo

Demonstration and predictions of perceived direction near an occluder.

  1. Free fuse the white square by uncrossing (left and middle figure) or crossing (middle and right figure) your eyes. Fixate the white square carefully and use the small vertical nonius lines to assess the accuracy of your vergence (they should appear vertically aligned). Notice the perceived shape of the rod.
  2. Hering's laws, strictly interpreted, predict that the middle section of the line will appear displaced leftward from the tops and bottoms.
  3. Erkelens' prediction, again strictly interpreted, is that the line will appear straight.
  4. Most people perceive a curved line.