Jovan Kemp^1,2 (), Bas Rokers^1,2; ¹Psychology, New York University Abu Dhabi, ²Center for Brain and Health, New York University Abu Dhabi

Accurate motion in depth perception is critical for interaction with the physical world. However, ~50% of individuals are unable to exploit binocular motion cues in part of their visual field - a type of apperceptive agnosia (Barendregt et al., 2014, Barendregt et al., 2016). Motion in depth stimuli contain two binocular cues. An interocular velocity difference (IOVD) cue, defined by differences in velocity of the two retinal projections, and a changing disparity (CD) cue based on differences in binocular disparity over time. Prior work has studied the contribution of these cues, but not under complete cue isolation conditions. Here, we leveraged a recently developed isolation technique, which exploits the periodic nature of gratings (Sheliga et al., 2016; Whritner et al., 2021). Participants judged the direction of gratings moving in depth (toward/away) as defined by either the full cue, or the IOVD/CD cues in isolation. Gratings were presented in the central 7.5 deg of the visual field at each of 32 locations (8 polar angles x 4 eccentricities). Sensitivity varied significantly both across and within observers. For all observers performance dropped with eccentricity across conditions (p = 0.002), as expected based on a decrease in retinal resolution. In addition, performance varied idiosyncratically across eccentricity-matched polar angle locations not easily captured by group level statistics. Finally, sensitivity in the full cue condition was best predicted by performance in the IOVD cue (p = 0.022), but not the CD cue (p = 0.1) condition, consistent with previous findings using cue-reduced stimuli. In all, isolating contributions of the two binocular cues to motion-in-depth are consistent with observed between- and within-participant variation in prior work. Our design provides an improved framework for identifying motion processing deficiencies in the human visual system, and may further our understanding of the neural basis of visual agnosias.

Acknowledgements: NYUAD Center for Brain and Health, funded by Tamkeen under NYU Abu Dhabi Research Institute grant CG012