Effects of reference objects and extra-retinal information about pursuit eye movements on curvilinear path perception from retinal flow

We have previously shown that when traveling on a circular path, observers use the rotation in the retinal velocity field for path curvature estimation and recover their path of forward travel relative to their perceived instantaneous heading (L. Li, & J. C. K. Cheng, 2011). Here, we examined the contribution of reference objects and extra-retinal information about pursuit eye movements to curvilinear path perception. In Experiment 1, the display simulated an observer traveling on a circular path over a textured ground with and without tall posts while looking at a fixed target on the future path, along heading, or along a fixed axis in the world. We found that reference objects did not help path perception. In Experiment 2, extra-retinal signals about pursuit eye movements were introduced in two viewing conditions: one that corresponded to the natural case of traveling on a circular path when the body orientation is aligned with the instantaneous heading and one that corresponded to the unnatural case of traveling when the body orientation is fixed relative to the world. We found that extra-retinal signals support accurate path perception only for the natural case of self-motion when the body orientation is aligned with heading such that pursuit compensation helps stabilize the heading in the body-centric coordinate system.