Auditory gating during visually-guided action?

We recently used an audiovisual illusion (Shams et al., 2000) during fast and accurate reaching movements and showed that susceptibility to the fusion illusion is reduced at high limb velocities (Tremblay and Nguyen, 2010). This study aimed to determine if auditory information processing is suppressed during voluntary action (Chapman and Beauchamp, 2006), which could explain reduced fusion during reaching movements. Instead of asking our participants () to report the number of flashes, we asked them to report the number of beeps (Andersen et al., 2004). Before each trial, participants were asked to fixate on a target LED presented on a horizontal reaching surface. The secondary stimuli combined 3 flash (0, 1, 2) by 2 beep (1, 2). During control tests, the secondary stimuli were presented at rest. In the experimental phase, stimuli were presented 0, 100 or 200 ms relative to the onset of a fast and accurate movement. Participants reported the number of beeps after each trial. A 3 flash × 2 beep × 4 presentation condition (0, 100, 200 ms + Control) ANOVA revealed that participants were less accurate at perceiving the actual number of beeps during the movement as compared to the control condition. More importantly, the number of flashes influenced the number of perceived beeps during the movement but not in the control condition. Lastly, no relationship was found between limb velocity and the number of perceived beeps. These results indicate that auditory information is significantly suppressed during goal-directed action but this mechanism alone fails to explain the link between limb velocity and the fusion illusion.