Proneness and methodological factors in body ownership illusions

Abstract

Researchers have long been enamoured with the nature of embodiment and perceptual experiences involving a distinctive change in one’s body-space perspective. Throughout the previous few decades, studies on out-of-body experiences (OBEs) and body ownership illusions (BOIs) have highlighted the prevalence of a wide range of body-self perceptual distortions occurring across populations. Numerous cognitive and neurological theories have been posited in order to explore the nature of embodiment. Furthermore, previous studies have indicated that particular factors, including verbal hallucinations and fantasy proneness, predispose some people to body ownership distortions such as OBEs. Other research has focused on the methodological factors that produce a realistic illusion of disembodiment, or body ownership transfer, to an external source. In order to investigate this field of research further, four experiments were conducted using variations of the Body Transfer Illusion (BTI) to evaluate conditions most conducive to having the experience of swapping bodies with another person. Individual differences were also investigated in order to explore one’s proneness to having a realistic experience of ownership transfer. The pilot experiment included seven participants and the findings demonstrated a significant relationship between a participant having had verbal hallucinations in the past and their immersion in the BTI. Experiment 1 had 15 participants and the results showed that a negative relationship exists between age and immersion in a newly-developed variation of the BTI, the Mirrored Body Illusion (MBI). Experiment 2 consisted of 40 participants and, consistent with Experiment 1, the results showed a negative association between age and immersion (i.e., increasing age was associated with a decrease in immersion in the illusion) across both the BTI and MBI configurations. An effect was also noted between schizotypy proneness and immersion in the BTI. Experiment 3 contained 20 participants, and the findings revealed a single variable which predicted immersion in both the BTI and MBI: Having a prior history of verbal hallucinations. Finally, a meta-analysis was performed on the aggregate data in Experiment 2 and 3 in order to ascertain patterns and commonalities across these two experiments. The variable most prominent in predicting one’s level of immersion in the BTI was age (a negative association was noted). Implications regarding individual differences and experimental conditions in BOIs are discussed. A body-self matrix model is emphasised to contextualise the role of individual differences discovered throughout the studies conducted. The role of multimodal matching in body representation is also critiqued, and a new visuospatial continuation principle is proposed. Finally, some of the remaining unanswered methodological and proneness questions in this field are considered.