Spatial modulation of audiovisual integration in the sound-induced flash illusion: A hierarchical drift diffusion modeling approach

The sound-induced flash illusion (SIFI) is a classic phenomenon in audiovisual integration research, reflecting the interactive mechanisms in multimodal information processing. This study aimed to recruit 30 healthy participants to explore the effects of sound and flash presentation frequencies and spatial location of stimuli on the perceptual decision-making. Previous studies have used illusion rate or accuracy as the core measurement indices, which fail to reflect the underlying cognitive processes of perceptual decision-making and thus have certain limitations. Therefore, this study aims to model the process of behavioral responses in the task. Among the perceptual decision-making models-Only the Hierarchical Drift Diffusion Model (HDDM) is suitable for the experimental task in this study. We used the drift rate, which reflects the speed of perceptual information accumulation in the model, as the core indicator. The results showed that both the sound-flash combinations and spatial location information significantly influenced evidence accumulation. Furthermore, the overall drift rate for right-side spatial presentation conditions was higher than for left-side conditions. The left-side advantage in B1F1 may reflect the right hemisphere's superiority in spatial attention, while the right-side advantage in B2F1 may reflect hemispheric differences in audiovisual integration. This study is the first to introduce HDDM in analyzing the spatial modulation mechanism within the SIFI paradigm, confirming that spatial location information not only has an independent main effect but can also interact with sensory combination factors to dynamically influence perceptual decision-making.