Depth information and perceived self-motion during simulated gaze rotations

When presented with random-dot displays with little depth information, observers cannot determine their direction of self-motion accurately in the presence of rotational flow without appropriate extra-retinal information (Royden CS et al. Vis Res 1994;34:3197-214.). On theoretical grounds, one might expect improved performance when depth information is added to the display (van den Berg AV and Brenner E. Nature 1994;371:700-2). We examined this possibility by having observers indicate perceived self-motion paths when the amount of depth information was varied. When stereoscopic cues and a variety of monocular depth cues were added, observers still misperceived the depicted self-motion when the rotational flow in the display was not accompanied by an appropriate extra-retinal, eye-velocity signal. Specifically, they perceived curved self-motion paths with the curvature in the direction of the simulated eye rotation. The distance to the response marker was crucial to the objective measurement of this misperception. When the marker distance was small, the observers' settings were reasonably accurate despite the misperception of the depicted self-motion. When the marker distance was large, the settings exhibited the errors reported previously by Royden CS et al. Vis Res 1994;34-3197-3214. The path judgement errors observers make during simulated gaze rotations appear to be the result of misattributing path-independent rotation to self-motion along a circular path with path-dependent rotation. An analysis of the information an observer could use to avoid such errors reveals that the addition of depth information is of little use.