Roles of Reference Object and Extraretinal Information in Path Perception from Optic Flow

In this study, we investigate the role of reference objects and extra-retinal information on path perception. In Experiment 1, the display simulated an observer traveling on a circular path over a textured ground or a textured ground with 20 posts (depth range: 5–20m). The simulated observer gaze direction was pointed to a target (1) on the path at 30° away from the initial heading, (2) at 15° outside of the path, (3) at 15° inside of the path, or (4) along the Z-axis of the simulated environment. Furthermore, path performance was similar for the two display conditions and consistent with our previous findings, indicating that reference objects did not help path perception. In Experiment 2, instead of pointing to the target, the simulated observer gaze direction pointed to the instantaneous heading thus the target moved on the screen rendering pursuit eye movements. Compared with data from Experiment 1, path performance was more accurate and less affected by path curvature, indicating that extraretinal signals improved path perception. We conclude that the presence of reference objects do not improve path perception when the scene contains rich optic flow information. Extraretinal information helps observers accurately estimate path rotation and thus contribute to accurate path perception.