Velocity Modulation of Optical Flow Affects Self-Motion Perception during Body Motion

Previous studies have shown that modifying visual information contributes to the on-line control of self-motion, and that vection can be induced by modifying the velocity of optical flow. In this study, we investigate whether velocity modulation of optical flow affects self-motion perception during whole-body motion. In our experiments, visual stimuli were provided by a virtual wall consisting of dots on a screen. The participants are asked to move their own head from a starting point to a goal in 1.5 sec (about 33 cm/s). We compared three conditions of visual feedback (optical flow) with/without modifications, ie,, accelerated, decelerated, and no change in optical flow. The rates of change in velocity were between 0.5 and 2 times the control condition. As a result, we found that the accelerated condition induced under-shooting, while the decelerated condition induced over-shooting relative to the control condition's goal point. Moreover, the positioning errors became largest with a change rate of 1.5 times. Our findings suggest that self-motion perception during body motion is influenced by the velocity change of the optical flow, and that there is an optimal rate of velocity change for perceiving a self-motion. Finally, we discuss the mechanism of integrating visual and proprioceptive information.