A New Angle on Object-Background Effects in Vection

Abstract

We considered whether optic flow generated by 3D relief of a foreground surface might influence visually-mediated self-motion perception (vection). We generated background motion consistent with self-rotation, and a foreground object with bumpy relief was either rotated with the observer (ego-centric) or fixed in world coordinates (world-centric). We found that vection strength ratings were greater in conditions with world-centric retinal motion of the foreground object, despite generating flow that was opposite to background motion. This effect was explained by observer judgments of the axis self-rotation in depth; whereas ego-centric flow generated experiences of more on-axis self-rotation, world-centric flow generated experiences of centrifugal rotation around the foreground object. These data suggest that foreground object motion can increase the perception of self-motion generated by optic flow, even when they reduce net retinal motion coherence and promote conditions for multisensory conflict. This finding supports the view that self-motion perception depends on mid-level representations of whole-scene motion.

Keywords: diffuse; reflectance; self-motion perception; specular; vection; vision.

Figure 1.

The arrangement of the simulated environment. (a) Schematic showing the organization of the background scene and foreground object relative to the observer. (b) Overview of simulated rotations of object and scene. Dashed arrows show direction of simulated physical rotation. Solid gray arrow shows the path of an observer’s perceived centrifugal orbit (rotation and translation) in the world-relief conditions. Note diagrams not to scale.

Figure 2.

Perceptual estimates of self-motion. (a) Mean location of perceived axis of rotation in depth (δ) for conditions with (red) or without fixation (blue) during presentation of ego-centric and world-centric relief. Larger values correspond to increasingly centrifugal rotation, whereas lower values correspond to increasingly on-center axis rotation. (b) Mean vection strength ratings for the same simulation and viewing conditions. Error bars show standard errors of the mean.

Figure 3.

Normalized vection strength estimates plotted as a function of perceived axis of (self-)rotation in depth. Line of best fit superimposed. Values for perceived axis location in depth range from 0.0 (observer-centred) to 1.0 (object-centred). Note the positive relationship between vection strength and perceived distance of the axis of rotation in depth (r = +0.56).