Self-other bodily merging in the context of synchronous but arbitrary-related multisensory inputs

A debated issue in the multisensory literature concerns the relative contribution of bottom-up sensory components versus top-down cognitive elaborations in contributing to the rise and persistency of bodily illusion. Previous studies, for instance, have shown that simultaneity of sensory inputs and plausibility of the stimulated object play an important role in the rubber hand phenomenon, whereas violation of tactile expectancy does not disrupt the illusory feeling to own a fake hand. The present research examined this issue in the context of the "enfacement" phenomenon (i.e., self-other face-perception modification), using entirely arbitrary and non-ecological pairs of visual and tactile events. Visual and tactile stimulation was matched in terms of spatial location, but not linked by any previously learned associations, making temporal synchrony a critical binding factor. Participants received electro-tactile stimulations on their cheek, while they watched the face of a stranger illuminated on the cheek with a dot of white light. Synchronous (vs. asynchronous) stimulations yielded the enfacement effect. In addition, the stranger stimulated in synchrony was judged as more similar, physically and in terms of personality, and as closer to the self. These findings suggest that synchronous multisensory stimulation on the face can produce both perceptual and social binding, even in the absence of any previously learned associations between the stimulations.