Dissertations, Theses, and Capstone Projects

Date of Degree

2-2026

Document Type

Master's Thesis

Degree Name

Master of Science

Program

Cognitive Neuroscience

Advisor

Tony Ro

Subject Categories

Cognition and Perception | Cognitive Neuroscience | Cognitive Science | Computational Neuroscience | Life Sciences

Keywords

Illusory touch, Multisensory integration, Somatosensory cortex, Functional magnetic resonance imaging (fMRI), Cross-modal perception, Visuotactile interaction

Abstract

Perceptual illusions arising from multisensory integration reveal how the brain constructs subjective experience from sensory input, and provide a powerful means of allowing the investigation of neural processes that track perceptual interpretation rather than physical stimulation alone. While visual illusions induced by auditory or tactile stimuli have been fairly well studied, the neural mechanisms underlying visually-induced illusory touch remain unclear. This study investigated whether illusory tactile perception engages the somatosensory cortex in a manner similar to veridical touch. Twenty healthy adults participated in an event-related functional magnetic resonance imaging (fMRI) study while performing a tactile numerosity judgment task. Each trial consisted of an initial visuotactile stimulus followed 100 ms later by one of four conditions: no stimulus, visual stimulus only, tactile stimulus only, or a combined visuotactile event. Participants reported the number of touches perceived, regardless of visual input. Behavioral results show that participants reported illusory touch on 54% of trials containing only a second visual stimulus, with substantial inter-individual variability. fMRI whole-brain analyses contrasted illusory touch versus veridical touch under matched physical stimulation, and this contrast revealed significant activation in the insular cortex and the adjacent rolandic operculum, which is part of the secondary somatosensory cortex. However, there was no detectable primary somatosensory cortex activation at the group level. In contrast, veridical perception across different physical conditions produced widespread activation across sensory and task-related networks. These findings suggest that visually-induced illusory touch arises from top-down integrative processes in higher-order multisensory regions rather than from the stimulus-driven activation of the primary somatosensory cortex. The results provide support for models of multisensory perception that emphasize probabilistic inference and indicate that illusory and veridical tactile percepts may engage distinct neural mechanisms.

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