Impact of Body Size Match to an Avatar on the Body Ownership Illusion and User's Subjective Experience

What I see and what I feel: the influence of deceptive visual cues and interoceptive accuracy on affective valence and sense of effort during virtual reality cycling

Background

How we feel during exercise is influenced by exteroceptive (e.g., vision) and interoceptive (i.e., internal body signals) sensory information, and by our prior experiences and expectations. Deceptive visual cues about one's performance during exercise can increase work rate, without negatively impacting affective valence (good/bad responses) or perceived exertion. However, what is less understood is whether the perception of the exercise experience itself can be shifted, if work rate is held constant. Here we aimed to investigate whether deceptive vision-via illusory hills in a virtual reality (VR) cycling experience-alters affective valence and perceived exertion when physical effort is controlled. We also evaluated whether the accuracy with which one detects interoceptive cues influences the extent to which deceptive visual information can shift exercise experiences.

Methods

A total of 20 participants (10 female; 30.2 ± 11.2 yrs) completed three VR cycling conditions each of 10-min duration, in a randomised, counterbalanced order. Pedal resistance/cadence were individualised (to exercise intensity around ventilatory threshold) and held constant across conditions; only visual cues varied. Two conditions provided deceptive visual cues about the terrain (illusory uphill, illusory downhill; resistance did not change); one condition provided accurate visual cues (flat terrain). Ratings of affective valence (Feeling Scale) and of perceived exertion (Borg's RPE) were obtained at standardised timepoints in each VR condition. Interoceptive accuracy was measured via a heartbeat detection test.

Results

Linear mixed effects models revealed that deceptive visual cues altered affective valence (f2 = 0.0198). Relative to flat terrain, illusory downhill reduced affective valence (Est = -0.21, p = 0.003), but illusory uphill did not significantly improve affective valence (Est = 0.107, p = 0.14). Deceptive visual cues altered perceived exertion, and this was moderated by the level of interoceptive accuracy (Condition-Interoception interaction, p = 0.00000024, f2 = 0.0307). Higher levels of interoceptive accuracy resulted in higher perceived exertion in the illusory downhill condition (vs flat), while lower interoceptive accuracy resulted in lower perceived exertion in both illusory hill conditions (vs flat) and shifts of greater magnitude.

Conclusions

Deceptive visual cues influence perceptual responses during exercise when physical effort does not vary, and for perceived exertion, the weighting given to visual exteroceptive cues is determined by accuracy with which interoceptive cues are detected. Contrary to our hypotheses, deceptive visual cues did not improve affective valence. Our findings suggest that those with lower levels of interoceptive accuracy experience most benefit from deceptive visual cues, providing preliminary insight into individualised exercise prescription to promote positive (and avoid negative) exercise experiences.

Impact of Personalized Avatars and Motion Synchrony on Embodiment and Users’ Subjective Experience: Empirical Study

Background

Embodiment through a virtual avatar is a key element for people to feel that they are in the virtual world.

Objective

This study aimed to elucidate the interaction between 2 methods of eliciting embodiment through a virtual avatar: motion synchronization and appearance similarity between a human and avatar, to understand embodiment (agency, body ownership, and self-location) and subjective experience (presence, simulator sickness, and emotion) in virtual reality.

Methods

Using a full-body motion capture system, 24 participants experienced their virtual avatars with a 3D-scanned face and size-matched body from a first-person perspective. This study used a 2 (motion; sync and async) × 2 (appearance; personalized and generic) within-subject design.

Results

The results indicated that agency and body ownership increased when motion and appearance were matched, whereas self-location, presence, and emotion were affected by motion only. Interestingly, if the avatar’s appearance was similar to the participants (personalized avatar), they formed an agency toward the avatar’s motion that was not performed by themselves.

Conclusions

Our findings would be applicable in the field of behavioral therapy, rehabilitation, and entertainment applications, by eliciting higher agency with a personalized avatar.

Younger and Older Adults’ Cognitive and Physical Functioning in a Virtual Reality Age Manipulation

Objectives: Age group stereotypes (AGS), especially those targeting old age, affect an individual’s behavior and long-term cognitive and physiological functioning. Conventional paradigms investigating the related mechanisms lack validity and stability. Our novel approach for the activation of self-relevant AGS uses a virtual reality (VR) ageing experience, measuring relevant effects on performance parameters.

Methods: In a between-subjects experimental design, young participants embodied either a younger or older avatar in a 3D virtual environment to capture the effects on physical (Study 1; N = 68) and cognitive performance (Study 2; N = 45). In Study 3 (N = 117), the paradigm was applied to older participants.

Results: For the younger participants, embodying older avatars was associated with declines in memory and physical performance when compared to the younger avatar age group. Furthermore, the manipulations’ main effects were moderated by negative explicit AGS that matched the respective performance domains. For the older participants, we found no significant performance differences in the two domains investigated.

Discussion: The experimental manipulation demonstrated an impact on relevant performance parameters on a motivational and strategic level, especially for strong performance-related AS, but for young participants only. Possible reasons and mechanisms for the differences in younger and older samples’ results are discussed.

Supervised learning for analysing movement patterns in a virtual reality experiment

The projection into a virtual character and the concomitant illusionary body ownership can lead to transformations of one's entity. Both during and after the exposure, behavioural and attitudinal changes may occur, depending on the characteristics or stereotypes associated with the embodied avatar. In the present study, we investigated the effects on physical activity when young students experience being old. After assignment (at random) to a young or an older avatar, the participants' body movements were tracked while performing upper body exercises. We propose and discuss the use of supervised learning procedures to assign these movement patterns to the underlying avatar class in order to detect behavioural differences. This approach can be seen as an alternative to classical feature-wise testing. We found that the classification accuracy was remarkably good for support vector machines with linear kernel and deep learning by convolutional neural networks, when inserting time sub-sequences extracted at random and repeatedly from the original data. For hand movements, associated decision boundaries revealed a higher level of local, vertical positions for the young avatar group, indicating increased agility in their performances. This occurrence held for both guided movements as well as achievement-orientated exercises.

Visual feedback improves movement illusions induced by tendon vibration after chronic stroke

BACKGROUND

Illusion of movement induced by tendon vibration is commonly used in rehabilitation and seems valuable for motor rehabilitation after stroke, by playing a role in cerebral plasticity. The aim was to study if congruent visual cues using Virtual Reality (VR) could enhance the illusion of movement induced by tendon vibration of the wrist among participants with stroke.

METHODS

We included 20 chronic stroke participants. They experienced tendon vibration of their wrist (100 Hz, 30 times) inducing illusion of movement. Three VR visual conditions were added to the vibration: a congruent moving virtual hand (Moving condition); a static virtual hand (Static condition); or no virtual hand at all (Hidden condition). The participants evaluated for each visual condition the intensity of the illusory movement using a Likert scale, the sensation of wrist's movement using a degree scale and they answered a questionnaire about their preferred condition.

RESULTS

The Moving condition was significantly superior to the Hidden condition and to the Static condition in terms of illusion of movement (p < 0.001) and the wrist's extension (p < 0.001). There was no significant difference between the Hidden and the Static condition for these 2 criteria. The Moving condition was considered the best one to increase the illusion of movement (in 70% of the participants). Two participants did not feel any illusion of movement.

CONCLUSIONS

This study showed the interest of using congruent cues in VR in order to enhance the consistency of the illusion of movement induced by tendon vibration among participants after stroke, regardless of their clinical severity. By stimulating the brain motor areas, this visuo-proprioceptive feedback could be an interesting tool in motor rehabilitation. Record number in Clinical Trials: NCT04130711, registered on October 17th 2019 ( https://clinicaltrials.gov/ct2/show/NCT04130711?id=NCT04130711&draw=2&rank=1 ).

Influence of virtual reality visual feedback on the illusion of movement induced by tendon vibration of wrist in healthy participants

Introduction

Illusion of movement induced by tendon vibration is an effective approach for motor and sensory rehabilitation in case of neurological impairments. The aim of our study was to investigate which modality of visual feedback in Virtual Reality (VR) associated with tendon vibration of the wrist could induce the best illusion of movement.

Methods

We included 30 healthy participants in the experiment. Tendon vibration inducing illusion of movement (wrist extension, 100Hz) was applied on their wrist during 3 VR visual conditions (10 times each): a moving virtual hand corresponding to the movement that the participants could feel during the tendon vibration (Moving condition), a static virtual hand (Static condition), or no virtual hand at all (Hidden condition). After each trial, the participants had to quantify the intensity of the illusory movement on a Likert scale, the subjective degree of extension of their wrist and afterwards they answered a questionnaire.

Results

There was a significant difference between the 3 visual feedback conditions concerning the Likert scale ranking and the degree of wrist’s extension (p<0.001). The Moving condition induced a higher intensity of illusion of movement and a higher sensation of wrist’s extension than the Hidden condition (p<0.001 and p<0.001 respectively) than that of the Static condition (p<0.001 and p<0.001 respectively). The Hidden condition also induced a higher intensity of illusion of movement and a higher sensation of wrist’s extension than the Static condition (p<0.01 and p<0.01 respectively). The preferred condition to facilitate movement’s illusion was the Moving condition (63.3%).

Conclusions

This study demonstrated the importance of carefully selecting a visual feedback to improve the illusion of movement induced by tendon vibration, and the increase of illusion by adding VR visual cues congruent to the illusion of movement. Further work will consist in testing the same hypothesis with stroke patients.

Controlling the Sense of Embodiment for Virtual Avatar Applications: Methods and Empirical Study

BACKGROUND

The sense of embodiment (SoE) is the feeling of one's own body, and research on the SoE extends from the rubber hand illusion to the full-body ownership illusion with a virtual avatar.

OBJECTIVE

The key to utilizing a virtual avatar is understanding and controlling the SoE, and it can be extended to several medical applications. In this study, we aimed to clarify these aspects by considering the following three subcomponents of SoE: sense of agency, ownership, and self-location.

METHODS

We defined a human avatar (HA), point light avatar (PLA), and out-of-body point light avatar (OBPLA) and compared them in three user studies. In study 1, 28 participants were recruited and the three avatar conditions (HA, PLA, and OBPLA) were compared. In study 2, 29 new participants were recruited, and there were two avatar conditions (HA ad PLA) and two motion synchrony conditions (synchrony and asynchrony). In study 3, 29 other participants were recruited, and there were two avatar conditions (PLA and OBPLA) and two motion synchrony conditions (synchrony and asynchrony). Dependent measures included sense of agency, ownership, and self-location; emotional response; presence; and simulator sickness.

RESULTS

The findings of study 1 showed that the three avatar generation methodologies can control the sense of ownership and self-location in a stepwise manner while maintaining a high sense of agency. In studies 2 and 3, we found dependencies among the three subcomponents of SoE and observed that they affected users' subjective experiences.

CONCLUSIONS

Our findings may have implications for boosting the effects of virtual avatar applications in medical areas, by understanding and controlling the SoE with a full-body illusion.