Yen-Tung Lee

This paper defends virtual veridicalism, according to which many perceptual experiences in virtual reality are veridical. My argument centers on perceptual variation, the phenomenon in which perceptual experience appears all the same while being reliably generated by different properties under different circumstances. It consists of three stages. The first stage argues that perceptual variation can occur in color perception without involving misperception. The second stage extends the argument to perceptual variation of space, arguing that it is possible for individuals to perceive distinct physical spaces as having the same experiential space without suffering from systematic misperception. The final stage proceeds to argue that perceptual variation without misperception in color and spatial perception can occur across virtual and ordinary environments. In that sense, given that ordinary experiences are presumably veridical, experiences in virtual reality are also veridical.

Virtual reality is poised to be increasingly important in our lives. This dissertation investigates the philosophical foundations of virtual reality, probing the metaphysics and epistemology of perceptual experiences of virtual environments. Specifically, it asks 1) what there is in virtual reality and 2) how we perceive virtual things. It defends virtual veridicalism, the view that perceptual experiences in virtual reality are as veridical as ordinary experiences. The defense consists of six chapters. Chapter 1 explains why such questions need to be addressed. Chapter 2 develops a realist view of virtual objects and properties, arguing that virtual objects exist and instantiate properties that may or may not be instantiated by ordinary physical objects. Chapter 3 presents an argument in defense of virtual veridicalism. I argue that the common criterion whereby we consider ordinary experiences veridical justifies the veridicality of perceptual experiences of virtual objects and properties. Chapter 4 looks for a representationalist account of perceptual content that could lend theoretical support to my defense of virtual veridicalism. I argue that none of the currently prominent representationalist views succeed. Rather, Chapter 5 proposes a new account — role representationalism — to achieve the goal. This account claims that, despite some differences in perceptual contents between the virtual and ordinary physical domains, a fundamental aspect of contents remains constant in perceptual experience across both domains, and it is the constant aspect that grounds the veridicality of perceptual experiences of virtual objects and properties. Chapter 6 assesses Chalmers’s (2017) defense of virtual veridicalism and argues that his defense cannot succeed unless presupposing role representationalism as the underlying theory of content of perceptual experiences. Finally, I conclude that 1) there are virtual objects and properties in virtual reality, and 2) we perceive these entities in a way that is as veridical as our perception of ordinary objects.

The distinction between the first-person perspective (1PP) and the third-person perspective (3PP) has been widely regarded as fundamental and rigid, and many researchers hold that genuine bodily illusions can only be experienced from the 1PP. We applied VR technology to investigate whether this mainstream view is correct. In our experiments, the participants were immersed in a VR environment in which they saw a life-sized virtual body either from the 1PP or from the 3PP. They either passively received tactile stimulations and/or actively interacted with a virtual soccer ball. Our VR system created novel visuo-motor-tactile correlations between the real and the virtual world: when the participant interacted with a real plastic soccer ball, he/she would feel corresponding tactile sensations and see the avatar performing the exact same movements. We found that a clear sense of ownership over the avatar was induced not only in the 1PP condition but also in the Passive-3PP and the Active-3PP conditions. We also observed evidence suggesting that it is possible to experience one’s body-location, 1PP-location, as well as self-location, both from the 1PP and from the 3PP. Together, we demonstrate that there is in fact no fundamental gap between embodied 1PP and embodied 3PP in the virtual world.

Body ownership concerns what it is like to feel a body part or a full body as mine, and has become a prominent area of study. We propose that there is a closely related type of bodily self-consciousness largely neglected by researchers—experiential ownership. It refers to the sense that I am the one who is having a conscious experience. Are body ownership and experiential ownership actually the same phenomenon or are they genuinely different? In our experiments, the participant watched a rubber hand or someone else’s body from the first-person perspective and was touched either synchronously or asynchronously. The main findings: (1) The sense of body ownership was hindered in the asynchronous conditions of both the body-part and the full-body experiments. However, a strong sense of experiential ownership was observed in those conditions. (2) We found the opposite when the participants’ responses were measured after tactile stimulations had ceased for 5 s. In the synchronous conditions of another set of body-part and full-body experiments, only experiential ownership was blocked but not body ownership. These results demonstrate for the first time the double dissociation between body ownership and experiential ownership. Experiential ownership is indeed a distinct type of bodily self-consciousness.

Self-location—the sense of where I am in space—provides an experiential anchor for one's interaction with the environment. In the studies of full-body illusions, many researchers have defined self-location solely in terms of body-location—the subjective feeling of where my body is. Although this view is useful, there is an issue regarding whether it can fully accommodate the role of 1PP-location—the sense of where my first-person perspective is located in space. In this study, we investigate self-location by comparing body-location and 1PP-location: using a head-mounted display (HMD) and a stereo camera, the subjects watched their own body standing in front of them and received tactile stimulations. We manipulated their senses of body-location and 1PP-location in three different conditions: the participants standing still (Basic condition), asking them to move forward (Walking condition), and swiftly moving the stereo camera away from their body (Visual condition). In the Walking condition, the participants watched their body moving away from their 1PP. In the Visual condition, the scene seen via the HMD was systematically receding. Our data show that, under different manipulations of movement, the spatial unity between 1PP-location and body-location can be temporarily interrupted. Interestingly, we also observed a “double-body effect.” We further suggest that it is better to consider body-location and 1PP-location as interrelated but distinct factors that jointly support the sense of self-location.

Recent studies of the rubber hand illusion (RHI) have shown that the sense of body ownership is constrained by several factors and yet is still very flexible. However, exactly how flexible is our sense of body ownership? In this study, we address this issue by investigating the following question: is it possible that one may have the illusory experience of owning four hands? Under visual manipulation, the participant adopted the experimenter’s first-person perspective (1PP) as if it was his/her own. Sitting face to face, the participant saw four hands—the experimenter’s two hands from the adopted 1PP together with the subject’s own two hands from the adopted third-person perspective (3PP). We found that: (1) the four-hand illusion did not occur in the passive four-hand condition. (2) In the active four-hand condition, the participants tapped their index fingers, imitated by the experimenter. When tactile stimulations were not provided, the key illusion was not induced, either. (3) Strikingly, once all four hands began to act with the same pattern and received synchronous tactile stimulations at the same time, many participants felt as if they had two more hands. These results show that the sense of body ownership is much more flexible than most researchers have suggested.

We investigate two issues about the subjective experience of one's body: first, is the experience of owning a full-body fundamentally different from the experience of owning a body-part?Second, when I experience a bodily sensation, does it guarantee that I cannot be wrong about whether it is me who feels it? To address these issues, we conducted a series of experiments that combined the rubber hand illusion (RHI) and the “body swap illusion.” The subject wore a head mounted display (HMD) connected with a stereo camera set on the experimenter's head. Sitting face to face, they used their right hand holding a paintbrush to brush each other's left hand. Through the HMD, the subject adopted the experimenter's first-person perspective (1PP) as if it was his/her own 1PP: the subject watched either the experimenter's hand from the adopted 1PP, and/or the subject's own hand from the adopted third-person perspective (3PP) in the opposite direction (180°), or the subject's full body from the adopted 3PP (180°, with or without face). The synchronous full-body conditions generate a “self-touching illusion”: many participants felt that “I was brushing my own hand!” We found that (1) the sense of body-part ownership and the sense of full-body ownership are not fundamentally different from each other; and (2) our data present a strong case against the mainstream philosophical view called the immunity principle (IEM). We argue that it is possible for misrepresentation to occur in the subject's sense of “experiential ownership” (the sense that I am the one who is having this bodily experience). We discuss these findings and conclude that not only the sense of body ownership but also the sense of experiential ownership call for further interdisciplinary studies.

In a recent study (Chen et al., 2018), we conducted a series of experiments that induced the “four-hand illusion”: using a head-mounted display (HMD), the participant adopted the experimenter’s first-person perspective (1PP) as if it was his/her own 1PP. The participant saw four hands via the HMD: the experimenter’s two hands from the adopted 1PP and the subject’s own two hands from the adopted third-person perspective (3PP). In the active four-hand condition, the participant tapped his/her index fingers, imitated by the experimenter. Once all four hands acted synchronously and received synchronous tactile stimulations at the same time, many participants felt as if they owned two more hands. In this paper, we argue that there is a philosophical implication of this novel illusion. According to Merleau-Ponty (1945/1962) and Legrand (2010), one can experience one’s own body or body-part either as-object or as-subject but cannot experience it as both simultaneously, i.e., these two experiences are mutually exclusive. Call this view the Experiential Exclusion Thesis. We contend that a key component of the four-hand illusion—the subjective experience of the 1PP-hands that involved both “kinesthetic sense of movement” and “visual sense of movement” (the movement that the participant sees via the HMD)—provides an important counter-example against this thesis. We argue that it is possible for a healthy subject to experience the same body-part both as-subject and as-object simultaneously. Our goal is not to annihilate the distinction between body-as-object and body-as-subject, but to show that it is not as rigid as suggested by the phenomenologists.