Multisensory Integration Dominates Hypnotisability and Expectations in the Rubber Hand Illusion

Area of Science:

• Neuroscience
• Psychology
• Cognitive Science

Background:

• Recent studies suggest the rubber hand illusion (RHI) may be primarily driven by hypnotic suggestibility and expectations (demand characteristics).
• These claims are based on analyses of a large study involving 353 participants and measures of hypnotisability using the Sussex-Waterloo Scale of Hypnotisability (SWASH).

Purpose of the Study:

• To re-examine the claims that hypnotic suggestibility and expectations are the main causes of the RHI.
• To determine the relative contributions of multisensory stimulation, hypnotisability, and expectations to the RHI.

Main Methods:

• Re-analysis of existing data from a large-scale RHI experiment with 353 participants.
• Inclusion of participants' expectancy ratings alongside SWASH scores and synchronous/asynchronous stimulation conditions.

Main Results:

• Synchronous multisensory stimulation consistently produced greater illusion and proprioceptive drift than asynchronous stimulation across all SWASH levels.
• Hypnotisability (SWASH scores) modestly influenced subjective illusion ratings, but did not explain the primary effect of stimulation synchrony.
• Expectations had a negligible effect on illusion ratings, with multisensory stimulation being the dominant factor (2-3 times stronger).

Conclusions:

• The rubber hand illusion is fundamentally a multisensory bodily illusion.
• While trait suggestibility can modulate the RHI, it is not the primary driver.
• Expectations play a minimal role in the experience of the RHI.