Introduction

In 1997, we were designing experiments to assess the stability of correspondence between points in the two retinas and the phenomenon of stereoscopic hysteresis (Diner and Fender, 1987; Fender and Julesz, 1967). As part of these experiments, we presented binocularly uncorrelated random-dot images to the two eyes in a stereoscope. Binocularly uncorrelated images produce a percept of noisy, incoherent depth, since there is no consistent disparity signal. However, when we moved the images in the two eyes laterally in opposing directions we obtained a compelling sense of coherent motion in depth. When the display was stopped, the stimulus again appeared as noisy depth. We quickly realized that the motion-in-depth percept was consistent with dichoptic motion cues in the stimulus. Thus, a compelling sense of changing depth can be supported by a stimulus that produces no coherent static depth. This was quite surprising, since experiments several years earlier had suggested that stereoscopic motion-in-depth perception could be fully explained by changes in disparity between correlated images. Unknown to us, Shioiri and colleagues had made similar findings, which they reported at the same Association for Research in Vision and Opthalmology (ARVO) meeting where we first presented our findings (Shioiri et al., 1998, 2000), although we found out they had also presented them earlier at a meeting in Japan. We performed a number of experiments on this phenomenon, reported as conference abstracts (Allison et al., 1998; Howard et al., 1998) that were subsequently cited.