When I Move, You (cognitively) Move': action observation and the fusion illusion.
53.552, Tuesday, May 14, 8:30 am - 12:30 pm, Vista Ballroom
Connor Reid1, Gerome A Manson1, Luc Tremblay1, Timothy N Welsh1; 1Faculty of Kinesiology & Physical Education, University of Toronto
In shared environments, one actors response may serve as an event code for an observer (Sebanz et al., 2003). This activated event code may then be used by the observer to simulate the performance of the actor. What remains to be determined, however, is if this observation-evoked simulation is confined to visual processing or if it extends to the processing of multisensory information. Shams et al. (2000; 2002) reported audio-visual phenomena in which conflicting auditory information biases visual perception. In the fusion illusion, a single flash and two beeps are erroneously perceived as two flashes, and in the fission illusion, two flashes and a single beep are perceived as one flash. Interestingly, Tremblay and Nguyen (2010) demonstrated that participants are more accurate at reporting the number of flashes when stimuli are presented at the portion of a goal-directed movement where limb velocity is highest. Given the proposed link between action and perception, the current experiment was designed to evaluate whether participants performance on these illusions would benefit from observing a goal-directed movement similar to Tremblay and Nguyen. Participants (n=12) fixated a target on the aiming board and reported the number of perceived flashes after either executing or observing an aiming movement. Audiovisual stimuli were presented at 0ms, 100ms, or 200ms relative to movement onset. Partly consistent with Tremblay and Nguyen, participants were more susceptible to the fusion illusion when the stimuli were presented late (200ms) relative to earlier in the trajectory (100ms). Critically, this pattern emerged in both performance and observation tasks. This finding is consistent with the hypothesis that observers simulate the performance of the actor and, hence, experience comparable alterations in multisensory processing. It is also possible, however, that the modulation of the illusion occurred because the limb displacement on the retina provided contrasting cues.