Yes / Motion-in-depth can be detected by using two different types of binocular cues: change of disparity (CD) and inter-ocular velocity differences (IOVD). To investigate the underlying detection mechanisms, stimuli can be constructed that isolate these cues or contain both (FULL cue). Two different methods to isolate the IOVD cue can be employed: anti-correlated (aIOVD) and de-correlated (dIOVD) motion signals. While both types of stimuli have been used in studies investigating the perception of motion-in-depth, for the first time, we explore whether both stimuli isolate the same mechanism and how they differ in their relative efficacy. Here, we set out to directly compare aIOVD and dIOVD sensitivity by measuring motion coherence thresholds. In accordance with previous results by Czuba et al. (2010), we found that motion coherence thresholds were similar for aIOVD and FULL cue stimuli for most participants. Thresholds for dIOVD stimuli, however, differed consistently from thresholds for the two other cues, suggesting that aIOVD and dIOVD stimuli could be driving different visual mechanisms.

Yes / Purpose: Two binocular sources of information serve motion-in-depth (MID) perception: changes in disparity over time (CD), and interocular velocity differences (IOVD). While CD requires the computation of small spatial disparities, IOVD could be computed from a much lower-resolution signal. IOVD signals therefore might still be available under conditions of binocular vision impairment (BVI) with limited or no stereopsis, e.g. amblyopia. Methods: Sensitivity to CD and IOVD was measured in adults who had undergone therapy to correct optical misalignment or amblyopia in childhood (n=16), as well as normal vision controls with good stereoacuity (n=8). Observers discriminated the interval containing a smoothly-oscillating MID “test” stimulus from a “control” stimulus in a two-interval forced choice (2IFC) paradigm. Results: Of the BVI observers with no static stereoacuity (n=9), one displayed evidence for sensitivity to IOVD only, while there was otherwise no sensitivity for either CD or IOVD in the group. Generally, BVI observers with measurable stereoacuity (n=7) displayed a pattern resembling the control group: showing a similar sensitivity for both cues. A neutral-density (ND) filter placed in front of the fixing eye in a subset of BVI observers did not improve performance. Conclusions: In one BVI observer there was preserved sensitivity to IOVD but not CD, though overall only those BVI observers with at least gross stereopsis were able to detect disparity-based or velocity-based cues to MID. The results imply that these logically distinct information sources are somehow coupled, and in some cases BVI observers with no stereopsis may still retain sensitivity to IOVD. / UK Biotechnology and Biological 498 Sciences Research Council (BBSRC): BB/M002543/1 (Alex R. Wade) BB/M001660/1 (Julie 499 M. Harris) and BB/M001210/1 (Marina Bloj)