Weighted visual and vestibular cues for spatial updating during passive self-motion

When walking or driving, it is of the utmost importance to continuously track the spatial relationship between objects in the environment and the moving body in order to prevent collisions. Although this process of spatial updating occurs naturally, it involves the processing of a myriad of noisy and ambiguous sensory signals. Here, using a psychometric approach, we investigated the integration of visual optic flow and vestibular cues in spatially updating a remembered target position during a linear displacement of the body. Participants were seated on a linear sled, immersed in a stereoscopic virtual reality environment. They had to remember the position of a target, briefly presented before a sideward translation of the body involving supra-threshold vestibular cues and whole-field optic flow that provided slightly discrepant motion information. After the motion, using a forced response participants indicated whether the location of a brief visual probe was left or right of the remembered target position. Our results show that in a spatial updating task involving passive linear self-motion humans integrate optic flow and vestibular self-displacement information according to a weighted-averaging process with, across subjects, on average about four times as much weight assigned to the visual compared to the vestibular contribution (i.e., 79% visual weight). We discuss our findings with respect to previous literature on the effect of optic flow on spatial updating performance