Section: New Results
Fidelity of Virtual Reality
MimeTIC wishes to promote the use of Virtual Reality to analyze and train human motor performance. It raises the fundamental question of the transfer of knowledge and skills acquired in VR to real life. In 2019, we put efforts in better understanding the potential fidelity of Virtual Reality experiences compared to real life experiences. It has been applied to various aspects of the interaction between pedestrians, but also the biomechanical fidelity of using haptic devices in highly constrainted conditions, such as hammering tasks.
Influence of Motion Speed on the Perception of Latency in Avatar Control
Participants : Ludovic Hoyet [contact] , Richard Kulpa, Anthony Sorel, Franck Multon.
With the dissemination of Head Mounted Display devices in which users cannot see their body, simulating plausible avatars has become a key challenge. For fullbody interaction, avatar simulation and control involves several steps, such as capturing and processing the motion (or intentions) of the user using input interfaces, providing the resulting user state information to the simulation platform, computing a plausible adaptation of the virtual world, rendering the scene, and displaying the multisensory feedback to the user through output interfaces. All these steps imply that the displayed avatar motion appears to users with a delay (or latency) compared to their actual performance. Previous works have shown an impact of this delay on the perception-action loop, with possible impact on Presence and embodiment. We have explored  how the speed of the motion performed when controlling a fullbody avatar can impact the way people perceive and react to such a delay. We conducted an experiment where users were asked to follow a moving object with their finger, while embodied in a realistic avatar. We artificially increased the latency by introducing different levels of delays (up to 300ms) and measured their performance in the mentioned task, as well as their feeling about the perceived latency. Our results show that motion speed influenced the perception of latency: we found critical latencies of 80ms for medium and fast motion speeds, while the critical latency reached 120ms for a slow motion speed. We also noticed that performance is affected by both latency and motion speed, with higher speeds leading to decreased performance. Interestingly, we also found that performance was affected by latency before the critical latency for medium and fast speeds, but not for a slower speed. These findings could help to design immersive environments to minimize the effect of latency on the performance of the user, with potential impacts on Presence and embodiment.
Influence of Personality Traits and Body Awareness on the Sense of Embodiment in Virtual Reality
Participants : Ludovic Hoyet [contact] , Rebecca Fribourg, Diane Dewez.
With the increasing use of avatars (i.e. the virtual representation of the user in a virtual environment) in virtual reality, it is important to identify the factors eliciting the sense of embodiment or the factors that can disrupt this feeling. This paper  reports an exploratory study aiming at identifying internal factors (personality traits and body awareness) that might cause either a resistance or a predisposition to feel a sense of embodiment towards a virtual avatar. To this purpose, we conducted an experiment (n=123) in which participants were immersed in a virtual environment and embodied in a gender-matched generic virtual avatar through a head-mounted display. After an exposure phase in which they had to perform a number of visuomotor tasks (during 2 minutes) a virtual character entered the virtual scene and stabbed the participants' virtual hand with a knife. The participants' sense of embodiment was measured, as well as several personality traits (Big Five traits and locus of control) and body awareness, to evaluate the influence of participants' personality on the acceptance of the virtual body. The major finding of the experiment is that the locus of control is linked to several components of embodiment: the sense of agency is positively correlated with an internal locus of control and the sense of body ownership is positively correlated with an external locus of control. Interestingly, both components are not influenced by the same traits, which confirms that they can appear independently. Taken together our results suggest that the locus of control could be a good predictor of the sense of embodiment when the user embodies an avatar with a similar physical appearance.
Gaze Behaviour During Person-Person Interaction in VR
Participants : Ludovic Hoyet, Anne-Hélène Olivier [contact] , Florian Berton.
Simulating realistic interactions between virtual characters has been of interest to research communities for years, and is particularly important to automatically populate virtual environments. This problem requires to accurately understand and model how humans interact, which can be difficult to assess. In this context, Virtual Reality (VR) is a powerful tool to study human behaviour, especially as it allows assessing conditions which are both ecological and controlled. While VR was shown to allow realistic collision avoidance adaptations, in the frame of the ecological theory of perception and action, interactions between walkers can not solely be characterized through motion adaptations but also through the perception processes involved in such interactions. The objective of this study  is therefore to evaluate how different VR setups influence gaze behaviour during collision avoidance tasks between walkers. In collaboration with Julien Pettré in Rainbow team, we designed an experiment involving a collision avoidance task between a participant and another walker (real confederate or virtual character). During this task, we compared both the participant’s locomotion and gaze behaviour in a real environment and the same situation in different VR setups (including a CAVE, a screen and a Head-Mounted Display) as illustrated on Figure4. Our results show that even if some quantitative differences exist, gaze behaviour is qualitatively similar between VR and real conditions. Especially, gaze behaviour in VR setups including a HMD is more in line with the real situation than the other setups. Furthermore, the outcome on motion adaptations confirms previous work, where collision avoidance behaviour is qualitatively similar in VR and real conditions. In conclusion, our results show that VR has potential for qualitative analysis of locomotion and gaze behaviour during collision avoidance. This opens perspectives in the design of new experiments to better understand human behaviour, in order to design more realistic virtual humans.
Gaze Anticipation in Curved Path in VR
Participants : Anne-Hélène Olivier [contact] , Hugo Brument.
This work was performed in collaboration with Ferran Argelaguet-Sanz and Maud Marchal from Hybrid team . We investigated whether the body anticipation synergies in real environments (REs) are preserved during navigation in virtual environments (VEs). Experimental studies related to the control of human locomotion in REs during curved trajectories report a top-down reorientation strategy with the reorientation of the gaze anticipating the reorientation of head, the shoulders and finally the global body motion. This anticipation behavior provides a stable reference frame to the walker to control and reorient whole-body according to the future direction. To assess body anticipation during navigation in VEs, we conducted an experiment where participants, wearing a head-mounted display, were asked to perform a lemniscate trajectory in a virtual environment (VE) using five different navigation techniques, including walking, virtual steering (hand, head or torso steering) and passive navigation. For the purpose of this experiment, we designed a new control law based on the powerlaw relation between speed and curvature during human walking. Taken together our results showed that a similar ordered top-down sequence of reorientation of the gaze, head and shoulders during curved trajectories between walking in REs and in VEs (for all the evaluated techniques). However, this anticipation mechanism significantly differs between physical walking in VE, where the anticipation is higher, and the other virtual navigation techniques. The results presented in this paper pave the way to the better understanding of the underlying mechanisms of human navigation in VEs and to the design of navigation techniques more adapted to humans
Validity of VR to Study Social Norms During Person-Person Interaction
Participants : Anne-Hélène Olivier [contact] , Ludovic Hoyet, Florian Berton.
The modelling of virtual crowds for major events, such as the Oympics in Paris in 2024, takes into account the global proxemics standards of individuals without questioning the possible variability of these standards according to the space in which the interactions are performed. We know that body interactions (Goffman, 1974) are subject to rules whose variability is, at least in part, cultural (Hall, 1971). Obviously, these proxemics standards also address practical issues such as available space and space occupancy density. Our objective in this study was to understand the conditions which can explain that the discomfort felt and the adaptive behaviour performed differ when the interaction takes place in the same city and in spaces with identical occupancy densities. Especially, we focused on the effect of the social context of the environement. We aim at estimating the extent to which the prospect of attending a sports performance alters sensitivity to the transgression of proxemics norms. An additional objective was to evaluate whether virtual reality can help us to provide new insights in such a social context, where objective measures out-of-the lab are complex to perform. To answer this question, we designed in collaboration with Julien Pettré (Rainbow team) and colleagues in the field of sociology François Le Yondre, Théo Rougant and Tristan Duverne (Univ Rennes II) an experiment (in real context and then in virtual reality) in two different locations: a train station and the surroundings of a stadium before a league 1 football match) but with similar densities. The task performed by a confederate was to walk and stand excessively close to men aged 20 to 40. The individual's behaviour (not conscious of being a subject of the experiment) was observed by ethnography and explanatory interviews were conducted immediately afterwards. This same experiment was carried out in virtual reality conditions on the same type of population, modelling the two spaces and making it possible to acquire more precise and quantifiable data than in real conditions such as distances, travel time and eye fixations. The results show that the discomfort shown is much higher in the train station. The sporting context seems to participate in a form of relaxation of the norms of bodily interaction. Such a gap is not observable in virtual reality. From a methodological point of view, explicit interviews make it possible to usefully identify the reasons why virtual reality does not generate the same reactions, although it sometimes provokes the same sensitivity. Future work is needed to evaluate the effect of an increased immersion on such Social Science studies.