Abstract
How much time does it take to voluntarily control the perception of bistable apparent motion? Addressing this issue could shed light on the dynamics of the intentional control of perception. We used tones to cue participants to engage their intentional control over the subsequently presented bistable rotation. The initial stimulus consisted of a pair of dots either vertically or horizontally arranged around the center of mass. In each trial, an auditory cue (a 300 Hz or 600 Hz tone) was presented, and after a variable delay (up to 1 s) the initial stimulus was replaced by its orthogonally arranged version. The change in the orientation of the dot arrangement caused a bistable percept of either clockwise or counterclockwise rotation. Participants were told to intend to see counterclockwise rotation after hearing the 300 Hz tone, and clockwise rotation after hearing the 600 Hz tone, then to report the actual direction of perceived rotation. As the delay between the auditory cue and the rotation onset became shorter, the ability to intentionally control perception decreased smoothly to near chance at no delay, but remained above chance at 200 ms. In a second experiment, we further demonstrated that the minimum time required for intentional control might be affected by subjective time. In this experiment, half of the trials were preceded by adaptation to a 5-s 5 Hz flicker known to cause subjective temporal dilation while the remaining trials were preceded by adaptation to a static stimulus. At the 0 ms cue-to-rotation delay, flicker adaptation resulted in significantly superior intentional control than did static adaptation. The systematic dependence of the intention effects on the cue-to-rotation delay and flicker adaptation precluded explanations based on response bias. In summary, intentional control of apparent motion requires less than 200 ms preparation, and its underlying mechanisms might be susceptible to factors affecting subjective time.
NIH R01 EY018197, NSF BCS 0643191.