Virtual swimming--breaststroke body movements facilitate vection

Visually induced illusory self-motion (vection) was facilitated by active breaststroke arm and body movements. Optic flow was generated by having the standing observer make these arm movements, which were detected by Kinect and incorporated into the display. When generated, this optic flow was either expanding (i.e. congruent with the observer's head motion) or contracting (i.e. incongruent with his/her head motion). Optic flow generated during these active movement conditions was also later played back to the observer during passive viewing conditions. On each of these trials, we recorded vection strength (latency, duration and magnitude). We found that: (i) both congruent and incongruent breaststroke movements increased vection (i.e. compared to passive viewing conditions); and (ii) congruent breaststroke movements increased vection more than incongruent ones. We name the enhancement provided by this type of active movement 'virtual swimming'. This demonstration shows that even unusual body movements can function as a self-motion signal.