Image Cyclorotation, Cyclovergence and Perceived Slant

Any stereoscopic imagery system must maintain the images in horizontal, vertical and torsional alignment. Humans maintain torsional alignment by rotating the eyes around the visual axes - a response known as cyclovergence. We have produced the first measurements of the dynamics of human cyclovergence and have shown that cyclovergence compensates well for low amplitude, low frequency torsional misalignments of binocular images.

We have also shown that cyclovergence is driven more by cyclorotations of horizontal lines than of vertical lines. Teleoperated systems should emulate this strategy because vertical disparities code slant in depth and should therefore by retained, whereas horizontal disparities arise only from misalignment of images and should therefore by nulled.

We have found that objective measurements of cyclovergence compare well with those obtained by a psychophysical nonius procedure. We have revealed conditions under which torsional misalignment of binocular images gives rise to illusory slant and propose a procedure for eliminating illusory slant.