The contribution of viewpoint oscillations to the perception of distance travelled from optic flow

• Bossard Martin
• Mestre Daniel

When exploring their environment, humans and other animals have the ability to use many sources of information to estimate the distance they travel. Several studies have shown that optic flow is a significant cue to perceive distance travelled. Furthermore, it was found that adding various viewpoint oscillations to a purely translational optic flow, simulating forward self-motion, modulated this perception. In a series of experiments, we tested whether the perception of distance travelled was also affected by viewpoint oscillation, similar to head motion during natural walking. A first series of experiments, participants were exposed to an immersive optic flow simulating forward self-motion and they were asked to indicate when they thought they had reached the remembered position of a previously seen target. The main conclusion from these experiments is that viewpoint oscillations improve the perception of distance travelled. Moreover, this effect appears to be linked to an increase in global retinal motion. However, the "ecological" contribution cannot be ruled out. Manipulating different viewpoint oscillation frequencies showed that the optimal performance was observed for a range of frequencies close to that observed for the head motion during natural walking. Two further experiments aimed to test whether the idiosyncrasy of viewpoint oscillations affects the perception of distance travelled in stationary observers and whether the absence of their own viewpoint oscillation played an important role in subjects' estimates, while they were walking on a treadmill. And finally, in a last experiment we tried to develop a dynamic measure of distance travelled to a previously seen target, with a continuous pointing task method. Overall, our results show that viewpoint oscillations play an important role in visual self-motion perception and that several parameters (including visual information, proprioceptive information and ecological aspects of natural walking) seem to be involved in this process.