Optic flow has an immediate and an enduring effect on the perceived straight ahead in the visual control of steering toward a goal

摘要

We examined whether the effect of optic flow on locomotion control can be indirect through recalibrating the perceived straight ahead (SA) and thus affecting the perceived target egocentric direction. The display (110?°Hx95?°V) simulated a participant walking over a textured ground plane at 2 m/s. In each 10-s trial, participants used a joystick to steer toward a target placed 25 m away within 15?° from their SA (i.e., their body midline). Their simulated heading in the display was displaced 10?° to the left or right of their SA. In Experiment 1, a vertical line was flashed for 100 ms at 0, 2.5, or 5 s after each trial, and 10 participants were asked to judge whether the line was to the left or right of their SA. A 2AFC adaptive procedure was used to find a point of subjective equality (PSE) representing the line position corresponding to the perceived SA. The staircases for left and right heading displacement were interleaved to prevent adaptation. The measured PSE was biased toward the displaced heading by 14%?±2% (mean?±SE) when the line is flashed immediately after the trial, by 7%?±1% at 2.5 s, and the bias disappeared at 5 s. In Experiment 2, 50 participants were asked to use a mouse to move a vertical line to their SA for three times before steering, and 5 s after steering for 20, 30, or 90 trials with left or right heading displacement. The judged SA shifted by 8%?±3%, 11%?±3%, and 23%?±4% of the heading displacement after 20, 30, and 90 trials of steering, respectively, and was mirrored by the change of the last 1-s heading error averaged across the first and the last 10 trials. We conclude that discrepant optic flow causes an immediate and an enduring shift of the perceived SA during locomotion.