De-Wei Dai¹, Po-Jang (Brown) Hsieh¹; ¹National Taiwan University

The intentional binding (IB) effect is the perceived shortening of time between a voluntary action and its sensory outcome. This study investigates the IB effect for different audiovisual sensory outcomes. Experiment 1 examines whether the perceived causality of sensory events affects the IB effect's magnitude. It employs a 2 x 2 repeated measures design: Action (Passive/Agency) and Event (Collision/Pass), using a modified IB task (Libet clock). We discovered that the IB effect for the sensory outcome is eliminated when the outcome includes both audio and visual modalities, regardless of perceived causality. The second experiment aims to determine whether this attenuation is due to multisensory integration or the divided attention nature of the paradigm. Experiment 2 employs a 2 x 3 repeated measures design: Action (Passive/Agency) and Event (Audio Only/Audiovisual Integrated/Audiovisual Irrelevant). The focus is on whether the IB magnitude (i.e., the difference between Passive and Agency) changes with the type of sensory event. Participants' primary task is to judge the onset of a collision sound. In the Audiovisual conditions, participants also assess the trajectory of two colored discs on the screen. In the Audiovisual Integrated condition, two discs launch toward center fixation and bounce away upon contact, with a simultaneous collision sound depicting a causal event. In the Audiovisual Irrelevant condition, two discs launch in pseudo-randomized directions, unrelated to the target sound. Results show that the IB magnitude is significantly weaker in both Audiovisual Integrated and Audiovisual Irrelevant conditions compared to Audio Only. The attenuation in the Audiovisual Irrelevant condition suggests that the effect is due to high perceptual load rather than multisensory integration.