Plausible Embodiment
"If I had this body, it would feel and work like this."
Virtual reality technology has aimed to simulate human sensorimotor input and output in order to reproduce interactions with virtual environments. User movements are tracked through sensors, executed by an avatar body, and the tactile and visual feedback the avatar should receive is conveyed back to the user through displays.
This approach works well when the user inhabits a humanoid avatar. However, it breaks down for non-human avatars. Humans have never lived with the body of an octopus, and therefore lack knowledge of how such a body should function or feel. Snakes sense heat through pit organs, but should a snake avatar present this to the user as visual information or thermal feedback? The authentic sensorimotor experience of non-human bodies is fundamentally unknowable to us, and therefore there is no correct reference to reproduce.
Therefore, to treat a non-human avatar as one's own body, we must move away from reproducing real sensorimotor experience and instead design interactions that mediate action and sensation between human and non-human bodies.
Framework: Expectation-Guided Design
I propose Plausible Embodiment as a design principle for non-human avatar experiences. Plausible Embodiment refers to a state in which a configuration of control and sensation within a non-human avatar body, differing in form from the human body, is accepted by the user as appropriate for that body and can be relied upon to use the avatar as one's own body. In short, the goal is to design experiences that lead users to the belief that "if I had this body, it would feel and work like this."
This framework leverages users' expectations toward avatar bodies — body cognition, stereotypes, and perceived affordances — as design resources. For example, when conveying the positional sensation of a tail, skin stretch feedback around the hips produces a deeper sense of immersion than vibration or purely visual cues. What creates this difference is the user's expectation of how such a sensation would be felt in that body.
Three Studies
Through three studies on control, sensation, and social practice, I have derived design insights on Plausible Embodiment across multiple layers of non-human avatar embodiment.
Plausible Control: Embodied Tentacle
This study investigated how different control mappings for an octopus-like virtual arm affect user experience. A 12-segment virtual arm was mapped one-to-one onto the 12 finger joints of the user's right hand across four conditions. Results revealed that mappings aligned with users' cognitive interpretations of the avatar body produced the most understandable and plausibly embodied control experience. For example, participants who perceived the little finger as the "tip" of the hand found mappings where the little finger controlled the tentacle tip more intuitive.
Plausible Sensation: Imaginary Joint
This study proposed reframing the boundary between a user's innate body and a virtual extension (such as a tail) as an "Imaginary Joint," delivering proprioceptive feedback through localized skin stretch. In a study with 21 participants comparing skin stretch against vibrotactile feedback, skin stretch produced more accurate perception and higher body ownership. Participants commented that "vibration just feels like a signal, whereas skin stretch feels like part of my body" and "if I had a tail, I imagine it would feel just like this," indicating that skin stretch supports Plausible Embodiment at the level of sensation more effectively than vibration.
Practices of Plausibility: Escape From Human
An interview study was conducted with non-human avatar users in Japanese VRChat communities. Users of centaurs, lamias, multi-armed creatures, and animal-form avatars revealed that they do not merely want to feel their avatar bodies — they desire to perceive and control them in ways that feel appropriate to those specific bodies. Furthermore, since existing communicative conventions cannot be directly applied to non-human forms, new forms of bodily communication are spontaneously emerging based on shared understandings of how those bodies should behave.
Future Directions
Going forward, I aim to further refine the requirements and varieties of plausibility across operation, sensation, and communication, and to explore additional layers. I also plan to investigate methods for measuring and shaping users' prior expectations as a means of designing more plausible experiences. By pre-establishing narratives or characteristics of a character, it may become possible to "install" new capabilities in users by shaping how those abilities are expected to feel and function.
The Plausible Embodiment framework is a design principle for creating believable experiences in non-human avatar embodiment, where no gold standard exists. Through this research, I aim to explore and extend the limits of human capabilities as they inhabit non-human entities.
Furthermore, related to the fact that humans and non-humans inhabit different Umwelten, the way individuals perceive the same external stimuli varies even among humans. For example, person A and person B may not experience the same "red." I hope this research can also contribute to understanding such perceptual diversity and mediating individual differences through technology.
If this vision resonates with you, feel free to reach out. I welcome collaborations and internships.
Shuto Takashita, PhD Year 2, Inami Lab, The University of Tokyo
@shike_cosmicXR
shuto.takashita@star.rcast.u-tokyo.ac.jp
