Body transfer illusions in the schizophrenia spectrum: a systematic review

Abstract

Schizophrenia has been viewed as a disorder of the self. Accordingly, the question arises if and how senses of ownership and agency are impaired in schizophrenia. To address this question, several body transfer illusions (BTIs) have been investigated in schizophrenia patients and other schizophrenia spectrum (SCZ-S) populations. The objective of the study was to systematically review the current evidence from BTIs in the SCZ-S. A systematic literature search in PubMed and CENTRAL (search date: February 12, 2022) was conducted on BTI studies carried out in SCZ-S populations. Studies were included if they were published in English after peer review, reported original research data, related to the SCZ-S, and used a BTI as its study method. Conference papers, study protocols, and reviews were excluded. For each included BTI study, various study characteristics and outcomes were retrieved, and a risk-of-bias score was calculated based on six study quality criteria. K = 40 studies were identified, of which k = 20 studies met the eligibility criteria. For BTI paradigms using visuotactile stimulation, most studies found elevated sense of ownership ratings in SCZ-S populations compared to healthy controls (HC). Implicit illusion measures (e.g., proprioceptive drift), in turn, did not generally indicate elevated embodiment levels in SCZ-S populations. Likewise, no consistent group differences emerged between SCZ-S populations and HC with respect to BTI paradigms using visuomotor stimulation. Furthermore, BTI vividness was found to correlate significantly with core symptoms of schizophrenia and various subclinical characteristics related to the SCZ-S. In line with the self-disturbance hypothesis, SCZ-S populations appear to be affected by aberrations in bodily self-awareness. Review registration: PROSPERO (identifier: CRD42022287960).

Mental Representations of the Body and Malleability of the Sense of Body Ownership in Schizophrenia within the Embodied Subject Model

“…It involves the manipulation of the sense of body ownership in a manner which, in effect, causes the illusion of the incorporation of an external object and initiates an important trend of research regarding the sense of body ownership. Studies of this type became a part of the body transfer illusion (BTI) paradigm (Baum et al, 2022). A short, 10-minute synchronous tactile stimulation of two upper limbs: one artificial, placed in front of the person, the other being the participant's own limb hidden from his vision, is sufficient for the person to start perceiving the artificial hand as their own.…”