Abstract
Brief auditory events can influence the perception of visual events (Shams et al. 2000). Also, humans are less susceptible to the fusion illusion (i.e., 2 flashes with 1 beep perceived as 1 flash) when stimuli are presented at high limb velocity during a reaching movement (Tremblay & Nguyen, 2010). In this study, we presented unimodal visual events to test the hypothesis that decreased susceptibility to an audio-visual illusion arises from absolute visual information processing up-regulation (cf. relative visual-to-auditory processing). Participants performed reaches towards a visual target (30 cm amplitude: 290-350 ms). A secondary visual stimulus presented in the lower visual field was constituted of one or two flashes (20 ms duration, 60 ms SOA) and presented at 0, 100, 200, 300, 400 or 500 ms relative to movement onset or at rest (i.e., control trials). Participants were asked to report whether they perceived one or two flashes after each trial. An ANOVA contrasted the perceived flashes using a 7 condition (control, 0-500 ms) by 2 flash (1-2) design. Post-hoc analyses of the condition by flash interaction showed that participants perceived: 1) more flashes during the movement (i.e., in all but the 300 ms condition) than at rest in the 1-flash trials and 2) fewer flashes during movement (i.e., at 200 and 300 ms only) than at rest in the 2-flash trials. Such decreased ability to accurately report the number of flashes was also observed across experimental conditions. These results represent evidence against the absolute visual up-regulation hypothesis.Acknowledgments: Canada Foundation for Innovation; Natural Sciences and Engineering Research Council of Canada