Experimental Induction of Micro- and Macrosomatognosia: A Virtual Hand Illusion Study

Abstract

Although body size misperceptions are known to occur under various neurological and psychiatric conditions, their neurocognitive underpinnings are not yet resolved. Accordingly, it would be beneficial to have an experimental paradigm, by which aberrant body misperceptions could be induced and systematically investigated. Expanding upon the “Virtual Hand Illusion” (VHI), this study aimed to design such a paradigm. Using a body-motion tracking system, we translated the participant's real hand position and movements to an embodiable, but resizable virtual hand model that we presented to the participants via a head-mounted display. The virtual hand's size was then systematically shrunk and enlarged in five different conditions (i.e., −50%, −25%, 0%, +25% or +50% rescaling). Applying this VHI derivate on n = 35 healthy participants, we investigated (1) if participants experience Sense of Ownership (SoO) and Sense of Agency (SoA) over a virtual hand that significantly deviates in size from their own hand, and (2) if by such size-deviant VHI induction, a change in their own hand size perception is also induced. Virtual hand embodiment was explicitly and implicitly assessed by means of self-report and EDA analysis. Questionnaire results revealed a stable SoA across all hand size conditions, while SoO parametrically decreased according to the hand scaling factor in either direction. Hand size perception, in turn, adapted according to the hand-scaling factor. In conclusion, the present study provides an important step toward an experimental paradigm that can induce and investigate aberrant body-size misperceptions.

Body transfer illusions in the schizophrenia spectrum: a systematic review

“…Implicit embodiment measures such as the proprioceptive drift (k = 8), somatosensory evoked potentials via electroencephalography (EEG) (k = 1), skin temperature (k = 1), the self-localization drift (k = 1), or the forearm bisection task (k = 1) were, in turn, used less often. Except for two studies in which skin temperature and EEG were obtained, no other physiological embodiment measures, such as the electrodermal fear response during artificial limb threatening [26][27][28] , were collected.…”

“…Therefore, future BTI research should include different implicit measures to operationalize the illusion. One promising approach is recording the participant's electrodermal activity while the virtual hand is threatened by a virtual syringe, as implemented in some BTI studies 26,27,57 and using this physiological marker as another implicit measure of artificial hand embodiment.…”

Design of an Immersive Virtual Reality Framework to Enhance the Sense of Agency Using Affective Computing Technologies

“…In ref. [122], the authors showed that users perceive the virtual hand as part of their own body and that the sense of agency is dependent on the delay and movement variability between their real and the virtual hand. Also, in ref.…”

“…Others, such as [119], highlight the importance of developing frameworks based on appraisal to manage cognitive models, which may be useful for managing intention when addressing the SoA. Also, other research, such as [97,120,122], suggests that the sense of agency can be improved by adapting the virtual environment to the users' body movements.…”