A mixed method investigation of the Rubber Hand Illusion

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Abstract

Embodiment is the experience of one’s own body. It is often studied using the Rubber Hand Illusion (RHI). This illusion varies the consistency between visual, tactile and proprioceptive signals to elicit a change to embodiment. Changes to embodiment are typically measured using a single sensory outcome measure of proprioceptive drift, which is interpreted as a proxy measure of embodiment. This approach obscures the unique contribution of other modalities such as vision and touch. The work presented in this thesis uses a mixed method approach to investigate the unique contribution of visual, tactile and proprioceptive modalities within the multisensory process of embodiment.In study one, a qualitative analysis showed that when visual-tactile discrepancies were present in the RHI, participants described both body ownership and body extension type changes to embodiment, and changes to tactile perception. In study two, psychophysical measurements of the RHI showed changes to visual, tactile and proprioceptive aspects of embodiment, suggesting that embodiment in the RHI could be measured using multiple sensory outcomes.Studies three and four assessed the utility of measuring multiple sensory outcomes of the RHI, by exploring changes to embodiment following internal and external forms of body perception training. Study three showed that brief body scan meditation, as a form of internal body perception training, reduced the longevity of the visual sensory outcome of the RHI and that this reduction was negatively correlated with improvements in interoceptive sensitivity. Study four showed that learning about the body through anatomical dissection training, as a form of external body perception training, reduced the longevity of the visual sensory outcome measure and decreased interoceptive sensitivity, but only in medical students who were high in trait personal distress. Collectively, these findings suggest that aspects of the multisensory processes of embodiment can become specialised and identify some unique contributions of individual sensory modalities to embodiment. The proprioceptive sensory outcome appears to be stable over time but the visual sensory outcome is a longer-term change to embodiment, which is susceptible to interference from body perception training. In study five, confirmatory factor analysis was used to assess the psychometric properties of an embodiment change questionnaire measuring body ownership, body extension and perceived causality in the RHI. Factor scores from the questionnaire were correlated with visual and proprioceptive outcome measures of the RHI and measures of trait empathy. The results suggested factor scores had better convergent validity than the standard illusion score used in previous research.This work has improved subjective and perceptual measures of the RHI and specified ways that individual sensory modalities provide a unique contribution to embodiment. The methods developed have further applications for studying the multisensory process of embodiment and investigating embodiment in a number of clinical groups.

Keyword(s)

Body perception ; Embodiment ; Interoceptive sensitivity ; Medical training ; Mindfulness; Mixed method ; Qualitative ; Rubber Hand Illusion

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