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Poster D in Poster Session D: Wednesday, August 5, 2:00 – 3:45 pm, Kimmel Center, Shorin & Rosenthal Rooms

Beyond Sensory Summation: How Expectations and Sensory Evidence Shape Multisensory Perception

Elizaveta Sycheva¹, Léa St-Gelais¹, Jérémy Brunel¹, Karim Jerbi¹, Shahab Bakhtiari¹, Franco Lepore¹, Vanessa Hadid²; ¹Université de Montréal, ²McGill University

Presenter: Elizaveta Sycheva

Perceptual decisions arise through the interplay of incoming sensory evidence and prior expectations. However, it remains unclear how this interaction shapes multisensory integration during the accumulation of decision evidence over time. Using dynamic audiovisual (AV) scenes in a semantic decision task, we examined how sensory reliability and semantic expectations influence decision-making. AV signals that were both coherent and congruent accelerated responses relative to unimodal conditions. This facilitation was strongest when visual input was degraded, consistent with increased reliance on joint AV contributions, as indicated by race-model violations demonstrating multisensory coactivation. Diffusion modeling revealed increased drift rates alongside longer non-decision times, indicating stronger evidence accumulation despite additional sensory processing, and resulting in faster overall responses. Together, these findings reveal that multisensory integration is not a fixed sensory-gain mechanism but a context-dependent coactivation process that selectively enhances evidence accumulation when signals converge on a shared semantic interpretation.

Topic Area: Decision-Making, Cognitive Control & Event Cognition