Institution: University of California Berkeley
Talk Title: Effects of Convergence and Monocular viewing on Perception of the Worldâs Horizontal and Vertical in Virtual Reality
Abstract: When we converge to look at a near target our eyes also typically undergo incyclotorsion where their top poles rotate towards the nose. In order to perceive orientations in the world accurately the visual system must take into account eye position and not rely only on the orientation of a stimulus on the retina. Here we utilized Virtual Reality (VR) to study how our perception is affected by cyclovergence. Subjects performed Subjective Visual Vertical (SVV) and Subjective Visual Horizontal (SVH) tasks using the FOVE0 VR headset at three head positions: upright, 20 degrees right-ear down and 20 degrees left-ear down. While they fixated on a head-fixed central target, subjects reported whether a line originating from the target, tilted between -12 to 12 degrees, was CW or CCW with respect to the world. The fixation target was presented binocularly while the stimulus line was presented either monocularly or binocularly at two vergence distances: 0.3m (near) or 1.5m (far). Near and far conditions were blocked while the other conditions were randomized. We found the mean difference in perceived vertical (SVV) between the left and right eye viewing conditions across all head positions to be 2.4 ± 0.3 degrees for near and 0.9 ± 0.3 degrees for far. The mean difference in perceived horizontal (SVH) between the left and right eye viewing across all head positions was 1.8 ± 0.4 degrees for near and 0.8 ± 0.3 degrees for far. That is, errors in perceived line orientation showed a CW bias in the left eye viewing condition and a CCW bias in the right eye viewing condition. These results show a bias in the monocular perception of the worlds horizontal and vertical consistent with the expected incyclotorsion at near viewing. Our findings suggest that the visual system does not utilize an extra retinal signal when assessing the orientation of a stimulus relative to the world presented monocularly in a VR setting.