In their letter, Kisielewska and Mirucka [1] point to a fundamental issue of virtual reality research: do experiences in virtual reality differ from real world experiences, and if so, should this be reflected in terminology we use to describe them? They make their case on body ownership and argue for a distinction of ownership experienced in real versus virtual reality. Although we support the claim that the aspect and subject of ownership which is investigated should always be stated clearly, we oppose to their call for distinguishing different types of ownership depending on the origin of their subject.
Body ownership describes the conscious awareness of having a body. Over the last decade, the traditional perspective of body representation being composed of body schema and body image has been replaced by a generally compatible but more integrative perspective [2, 3]. In this notion, which is also picked up by Kisielewska and Mirucka [1], body ownership emerges through a conglomerate of different body representations, informed by multisensory information plus cognitive-emotional processes. Importantly, the relation between physical input and the experience of ownership is comparable to any other sensory experience – a result of quantifiable sensory input processed with individual preferences and cognitions.
There are various ways to induce ownership illusions, and mechanistically speaking, they overlap considerably. Irrespective of the implementation through an obesity suit [4], a rubber hand [5], a movie [6, 7], or a virtual avatar [8‒10], all illusions work through the combination about altered visual information about the body combined with another sensory modality, usually either locomotion or touch. In all cases, the congruent multisensory information is combined with cognitions and emotions about the owned body (part) to an ownership experience. Notably, phenomena associated to body ownership have been observed irrespective of the presentation modality used to create an ownership illusion [8]. The distinction proposed by Kisielewska and Mirucka [1] negates the probably identical quality of embodiment in all these cases and sacrifices a mechanistically plausible terminology to a deceptive clarity.
Instead of focusing on the terminology of how an ownership illusion was technically implemented, we advocate efforts to standardize procedures on describing ownership induced through the respective method. Ownership illusions are relative illusions, and even successful illusions do not replace the sense for the physical body [8]. Hence, for the evaluation of their implementation and their effectiveness, quantification of the strength of the illusion can be crucial. Clinical studies are currently heterogeneous in whether and how they assess ownership measures: while some authors used a Visual Analogue Scale [9], others [10, 11] used a questionnaire filed from the assessment suggested by Piryankova and colleagues [8]. If studies using embodiment illusions observe different effects, methodological differences in how these illusions were produced need to be considered. However, from a mechanistic point of view, it is not relevant how the illusion was produced, but how successful it was.
Conflict of Interest Statement
The authors have no conflicts of interest to declare.
Funding Sources
This study was not supported by any sponsor or funder.
Author Contributions
S.C.B., K.E.G., and S.Z. conceptualized the letter and reviewed and edited the manuscript. S.C.B. wrote the original draft.