Body-ownership and visual perception

The idea that our body plays an important role in visual perception has a long history in storytelling and philosophy. Some ideas are very intuitive. For example, few will disagree with the notion that smaller people perceive the world to be bigger, and vice versa, that larger people perceive the world to be smaller. In contrast, more controversial ideas regarding the role of our body in visual perception have been debated by philosophers. According to these philosophers, the very nature of visual perception lies in the fact that we have a body that moves in space. Since George Berkeley (1685 – 1753) first formalized such a fundamental role for our body in visual perception, different philosophical theories have branched out to account for the latest scientific findings. Although experimental psychologists and neuroscientists have long neglected these intriguing philosophical accounts, the recent development of body-ownership illusions allowed for a more rigorous investigation of the supposed link between our body and visual perception. In body-ownership illusions, research participants experience an artificial body (or body-part) to be their own. These illusions allow for the dissociation between the subjective experience that your body belongs to you (i.e. body-ownership) and the mere visual impression of your body from a first-person perspective. The studies that comprise this thesis use different ownership illusions to investigate the role of body-ownership in visual perception, and the role of visual perception in body-ownership, with visual perception being an umbrella-term for both visuospatial perception and visual awareness. In Study I and Study II we investigated the mechanisms by which body-size influences the perceived size of the world, by having participants experience ownership of different sized (and sometimes invisible) bodies. Our results show that this own-body-size effect does not rely on visual information per se, but instead, on the recalibration between visual and tactile information that updates the representation of external space. In Study III we combine the rubber hand illusion with binocular rivalry to show that body-ownership promotes visual awareness of a fake hand. And in Study IV we combine the rubber hand illusion with continuous flash suppression to show that ownership can be induced in the absence of visual awareness. Such unconscious ownership calls for a reevaluation of the standard definition of body-ownership. Taken together, these studies illuminate the intricate relationship between body-ownership and visual perception. In addition to the scientific research fields of visuospatial perception, visual awareness, and body-ownership, these results are valuable to the philosophical debate on the nature of visual perception and might provide future applications in clinical psychology

The 'not-so-strange' body in the mirror: : A principal components analysis of direct and mirror self-observation

This document is the Accepted Manuscript version of the following article: Paul M. Jenkinson, and Catherine Preston, ‘The “not-so-strange” body in the mirror: A principal components analysis of direct and mirror self-observation’, Consciousness and Cognition, Vol. 48, pp. 262-272, first published online 4 January 2017, doi: http://dx.doi.org/10.1016/j.concog.2016.12.007 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.In this study we adopted a psychometric approach to examine how the body is subjectively experienced in a mirror. One hundred and twenty-four healthy participants viewed their body for five minutes directly or via a mirror, and then completed a 20-item questionnaire designed to capture subjective experiences of the body. PCA revealed a two-component structure for both direct and mirror conditions, comprising body evaluations (and alienation) and unusual feelings and perceptions. The relationship between these components and pre-existing tendencies for appearance anxiety, body dysmorphic-type beliefs, dissociative symptomatology, self-objectification and delusion ideation further supported the similarity between direct and mirror conditions; however, the occurrence of strange experiences like those reported to occur during prolonged face viewing was not confirmed. These results suggest that, despite obvious differences in visual feedback, observing the body via a mirror (as an outside observer) is subjectively equivalent to observing the body directly (from our own viewpoint).Peer reviewedFinal Accepted Versio

Owning an overweight or underweight body: distinguishing the physical, experienced and virtual body

Our bodies are the most intimately familiar objects we encounter in our perceptual environment. Virtual reality provides a unique method to allow us to experience having a very different body from our own, thereby providing a valuable method to explore the plasticity of body representation. In this paper, we show that women can experience ownership over a whole virtual body that is considerably smaller or larger than their physical body. In order to gain a better understanding of the mechanisms underlying body ownership, we use an embodiment questionnaire, and introduce two new behavioral response measures: an affordance estimation task (indirect measure of body size) and a body size estimation task (direct measure of body size). Interestingly, after viewing the virtual body from first person perspective, both the affordance and the body size estimation tasks indicate a change in the perception of the size of the participant’s experienced body. The change is biased by the size of the virtual body (overweight or underweight). Another novel aspect of our study is that we distinguish between the physical, experienced and virtual bodies, by asking participants to provide affordance and body size estimations for each of the three bodies separately. This methodological point is important for virtual reality experiments investigating body ownership of a virtual body, because it offers a better understanding of which cues (e.g. visual, proprioceptive, memory, or a combination thereof) influence body perception, and whether the impact of these cues can vary between different setups

If I were a grown-up: Children's response to the Rubber Hand Illusion with different hand sizes

During childhood, children’s bodies undergo rapid physical growth, which may affect their ability to accurately perceive their own bodies as well as the external environment. Concurrently, multisensory processes underlying bodily self-consciousness gradually develop. However, little is known of the relation between changes in body size and corresponding update in bodily self-consciousness. In this study, 6- to 8-year-old children experienced the “rubber hand illusion” while watching a regular (child-like) or larger (adult-like) rubber hand being touched either synchronously or asynchronously with their own real hand. We measured proprioceptive drift and subjective ownership as well as changes in weight estimation of objects. Synchronous versus asynchronous visuotactile stroking with both the regular and larger hands caused a change in subjective body ownership but did not make a difference in perceived hand location and weight estimation of objects having the same size but different weight. Intriguingly, simply viewing the regular hand led to greater proprioceptive drift and to overestimation of the objects’ weight relative to the larger hand. In addition, weight estimation was also influenced by hand size after visuotactile stroking. These results demonstrate that visuotactile information modulates the intrinsic properties of body representation in terms of size in children and further corroborate previous findings suggesting late developing optimal calibration of visual and proprioceptive signals

Being Barbie: The Size of One’s Own Body Determines the Perceived Size of the World

A classical question in philosophy and psychology is if the sense of one's body influences how one visually perceives the world. Several theoreticians have suggested that our own body serves as a fundamental reference in visual perception of sizes and distances, although compelling experimental evidence for this hypothesis is lacking. In contrast, modern textbooks typically explain the perception of object size and distance by the combination of information from different visual cues. Here, we describe full body illusions in which subjects experience the ownership of a doll's body (80 cm or 30 cm) and a giant's body (400 cm) and use these as tools to demonstrate that the size of one's sensed own body directly influences the perception of object size and distance. These effects were quantified in ten separate experiments with complementary verbal, questionnaire, manual, walking, and physiological measures. When participants experienced the tiny body as their own, they perceived objects to be larger and farther away, and when they experienced the large-body illusion, they perceived objects to be smaller and nearer. Importantly, despite identical retinal input, this “body size effect” was greater when the participants experienced a sense of ownership of the artificial bodies compared to a control condition in which ownership was disrupted. These findings are fundamentally important as they suggest a causal relationship between the representations of body space and external space. Thus, our own body size affects how we perceive the world

Learning empathy through virtual reality : Multiple strategies for training empathy-related abilities using body ownership Illusions in embodied virtual reality

Several disciplines have investigated the interconnected empathic abilities behind the proverb “to walk a mile in someone else’s shoes” to determine how the presence, and absence, of empathy-related phenomena affect prosocial behavior and intergroup relations. Empathy enables us to learn from others’ pain and to know when to offer support. Similarly, virtual reality (VR) appears to allow individuals to step into someone else’s shoes, through a perceptual illusion called embodiment, or the body ownership illusion. Considering these perspectives, we propose a theoretical analysis of different mechanisms of empathic practices in order to define a possible framework for the design of empathic training in VR. This is not intended to be an extensive review of all types of practices, but an exploration of empathy and empathy-related phenomena. Empathy-related training practices are analyzed and categorized. We also identify different variables used by pioneer studies in VR to promote empathy-related responses. Finally, we propose strategies for using embodied VR technology to train specific empathy-related abilities

Up, down, near, far: an online vestibular contribution to distance judgement

Whether a visual stimulus seems near or far away depends partly on its vertical elevation. Contrasting theories suggest either that perception of distance could vary with elevation, because of memory of previous upwards efforts in climbing to overcome gravity, or because of fear of falling associated with the downwards direction. The vestibular system provides a fundamental signal for the downward direction of gravity, but the relation between this signal and depth perception remains unexplored. Here we report an experiment on vestibular contributions to depth perception, using Virtual Reality. We asked participants to judge the absolute distance of an object presented on a plane at different elevations during brief artificial vestibular inputs. Relative to distance estimates collected with the object at the level of horizon, participants tended to overestimate distances when the object was presented above the level of horizon and the head was tilted upward and underestimate them when the object was presented below the level of horizon. Interestingly, adding artificial vestibular inputs strengthened these distance biases, showing that online multisensory signals, and not only stored information, contribute to such distance illusions. Our results support the gravity theory of depth perception, and show that vestibular signals make an on-line contribution to the perception of effort, and thus of distance