Stephan Streuber

The influence of avatar (self and character) animations on distance estimation, object interaction and locomotion in immersive virtual environments

Humans have been shown to perceive and perform actions differently in immersive virtual environments (VEs) as compared to the real world. Immersive VEs often lack the presence of virtual characters; users are rarely presented with a representation of their own body and have little to no experience with other human avatars/characters. However, virtual characters and avatars are more often being used in immersive VEs. In a two-phase experiment, we investigated the impact of seeing an animated character or a self-avatar in a head-mounted display VE on task performance. In particular, we examined performance on three different behavioral tasks in the VE. In a learning phase, participants either saw a character animation or an animation of a cone. In the task performance phase, we varied whether participants saw a co-located animated self-avatar. Participants performed a distance estimation, an object interaction and a stepping stone locomotion task within the VE. We find no impact of a character animation or a self-avatar on distance estimates. We find that both the animation and the self-avatar influenced task performance which involved interaction with elements in the environment; the object interaction and the stepping stone tasks. Overall the participants performed the tasks faster and more accurately when they either had a self-avatar or saw a character animation. The results suggest that including character animations or self-avatars before or during task execution is beneficial to performance on some common interaction tasks within the VE. Finally, we see that in all cases (even without seeing a character or self-avatar animation) participants learned to perform the tasks more quickly and/or more accurately over time.

Putting Actions in Context: Visual Action Adaptation Aftereffects Are Modulated by Social Contexts

The social context in which an action is embedded provides important information for the interpretation of an action. Is this social context integrated during the visual recognition of an action? We used a behavioural visual adaptation paradigm to address this question and measured participants’ perceptual bias of a test action after they were adapted to one of two adaptors (adaptation after-effect). The action adaptation after-effect was measured for the same set of adaptors in two different social contexts. Our results indicate that the size of the adaptation effect varied with social context (social context modulation) although the physical appearance of the adaptors remained unchanged. Three additional experiments provided evidence that the observed social context modulation of the adaptation effect are owed to the adaptation of visual action recognition processes. We found that adaptation is critical for the social context modulation (experiment 2). Moreover, the effect is not mediated by emotional content of the action alone (experiment 3) and visual information about the action seems to be critical for the emergence of action adaptation effects (experiment 4). Taken together these results suggest that processes underlying visual action recognition are sensitive to the social context of an action.

Assessing body image in anorexia nervosa using biometric self-avatars in virtual reality: Attitudinal components rather than visual body size estimation are distorted

Background Body image disturbance (BID) is a core symptom of anorexia nervosa (AN), but as yet distinctive features of BID are unknown. The present study aimed at disentangling perceptual and attitudinal components of BID in AN. Methods We investigated n = 24 women with AN and n = 24 controls. Based on a three-dimensional (3D) body scan, we created realistic virtual 3D bodies (avatars) for each participant that were varied through a range of ±20% of the participants’ weights. Avatars were presented in a virtual reality mirror scenario. Using different psychophysical tasks, participants identified and adjusted their actual and their desired body weight. To test for general perceptual biases in estimating body weight, a second experiment investigated perception of weight and shape matched avatars with another identity. Results Women with AN and controls underestimated their weight, with a trend that women with AN underestimated more. The average desired body of controls had normal weight while the average desired weight of women with AN corresponded to extreme AN (DSM-5). Correlation analyses revealed that desired body weight, but not accuracy of weight estimation, was associated with eating disorder symptoms. In the second experiment, both groups estimated accurately while the most attractive body was similar to Experiment 1. Conclusions Our results contradict the widespread assumption that patients with AN overestimate their body weight due to visual distortions. Rather, they illustrate that BID might be driven by distorted attitudes with regard to the desired body. Clinical interventions should aim at helping patients with AN to change their desired weight.

The effect of social context on the use of visual information

Social context modulates action kinematics. Less is known about whether social context also affects the use of task relevant visual information. We tested this hypothesis by examining whether the instruction to play table tennis competitively or cooperatively affected the kind of visual cues necessary for successful table tennis performance. In two experiments, participants played table tennis in a dark room with only the ball, net, and table visible. Visual information about both players’ actions was manipulated by means of self-glowing markers. We recorded the number of successful passes for each player individually. The results showed that participants’ performance increased when their own body was rendered visible in both the cooperative and the competitive condition. However, social context modulated the importance of different sources of visual information about the other player. In the cooperative condition, seeing the other player’s racket had the largest effects on performance increase, whereas in the competitive condition, seeing the other player’s body resulted in the largest performance increase. These results suggest that social context selectively modulates the use of visual information about others’ actions in social interactions.

Does Brief Exposure to a Self-avatar Affect Common Human Behaviors in Immersive Virtual Environments?

A plausible assumption is that self-avatars increase the realism of immersive virtual environments (VEs), because self-avatars provide the user with a visual representation of his/her own body. Consequently having a self-avatar might lead to more realistic human behavior in VEs. To test this hypothesis we compared human behavior in VE with and without providing knowledge about a self-avatar with real human behavior in real-space. This comparison was made for three tasks: a locomotion task (moving through the content of the VE), an object interaction task (interacting with the content of the VE), and a social interaction task (interacting with other social entities within the VE). Surprisingly, we did not find effects of a self-avatar exposure on any of these tasks. However, participant’s VE and real world behavior differed significantly. These results challenge the claim that knowledge about the self-avatar substantially influences natural human behavior in immersive VEs.

Perception of strength and power of realistic male characters

We investigated the influence of body shape and pose on the perception of physical strength and social power for male virtual characters. In the first experiment, participants judged the physical strength of varying body shapes, derived from a statistical 3D body model. Based on these ratings, we determined three body shapes (weak, average, and strong) and animated them with a set of power poses for the second experiment. Participants rated how strong or powerful they perceived virtual characters of varying body shapes that were displayed in different poses. Our results show that perception of physical strength was mainly driven by the shape of the body. However, the social attribute of power was influenced by an interaction between pose and shape. Specifically, the effect of pose on power ratings was greater for weak body shapes. These results demonstrate that a character with a weak shape can be perceived as more powerful when in a high-power pose.

Creating Body Shapes From Verbal Descriptions by Linking Similarity Spaces

Brief verbal descriptions of people’s bodies (e.g., “curvy,” “long-legged”) can elicit vivid mental images. The ease with which these mental images are created belies the complexity of three-dimensional body shapes. We explored the relationship between body shapes and body descriptions and showed that a small number of words can be used to generate categorically accurate representations of three-dimensional bodies. The dimensions of body-shape variation that emerged in a language-based similarity space were related to major dimensions of variation computed directly from three-dimensional laser scans of 2,094 bodies. This relationship allowed us to generate three-dimensional models of people in the shape space using only their coordinates on analogous dimensions in the language-based description space. Human descriptions of photographed bodies and their corresponding models matched closely. The natural mapping between the spaces illustrates the role of language as a concise code for body shape that captures perceptually salient global and local body features.

Body size estimation of self and others in females varying in BMI

Previous literature suggests that a disturbed ability to accurately identify own body size may contribute to overweight. Here, we investigated the influence of personal body size, indexed by body mass index (BMI), on body size estimation in a non-clinical population of females varying in BMI. We attempted to disentangle general biases in body size estimates and attitudinal influences by manipulating whether participants believed the body stimuli (personalized avatars with realistic weight variations) represented their own body or that of another person. Our results show that the accuracy of own body size estimation is predicted by personal BMI, such that participants with lower BMI underestimated their body size and participants with higher BMI overestimated their body size. Further, participants with higher BMI were less likely to notice the same percentage of weight gain than participants with lower BMI. Importantly, these results were only apparent when participants were judging a virtual body that was their own identity (Experiment 1), but not when they estimated the size of a body with another identity and the same underlying body shape (Experiment 2a). The different influences of BMI on accuracy of body size estimation and sensitivity to weight change for self and other identity suggests that effects of BMI on visual body size estimation are self-specific and not generalizable to other bodies.

Tech-note: Iterative design and test of a multimodal experience

The goal of the Turtlesurf project described in this tech-note is to design, implement and evaluate a multimodal installation that should provide a good user experience in a virtual 3D world. For this purpose we combine audio-visual media forms and different types of haptic/tactile feedback. For the latter, we focus on the application of vibrational feedback, wind and water spray and heat. We follow a user-centered design approach and try to get user feedback as early as possible during the iterative design process. We present the conceptual idea of the Turtlesurf project, and the iterative design and test of prototypes that helped us to refine the final design based on collected user feedback.

The influence of visual information on the motor control of table tennis strokes

Theories of social interaction (i.e., common coding theory) suggest that visual information about the interaction partner is critical for successful interpersonal action coordination. Seeing the interaction partner allows an observer to understand and predict the interaction partners behavior. However, it is unknown which of the many sources of visual information about an interaction partner (e.g., body, end effectors, and/or interaction objects) are used for action understanding and thus for the control of movements in response to observed actions. We used a novel immersive virtual environment to investigate this further. Specifically, we asked participants to perform table tennis strokes in response to table tennis balls stroked by a virtual table tennis player. We tested the effect of the visibility of the ball, the paddle, and the body of the virtual player on task performance and movement kinematics. Task performance was measured as the minimum distance between the center of the paddle and the center of the ball (radial error). Movement kinematics was measured as variability in the paddle speed of repeatedly executed table tennis strokes (stroke speed variability). We found that radial error was reduced when the ball was visible compared to invisible. However, seeing the body and/or the racket of the virtual players only reduced radial error when the ball was invisible. There was no influence of seeing the ball on stroke speed variability. However, we found that stroke speed variability was reduced when either the body or the paddle of the virtual player was visible. Importantly, the differences in stroke speed variability were largest in the moment when the virtual player hit the ball. This suggests that seeing the virtual players body or paddle was important for preparing the stroke response. These results demonstrate for the first time that the online control of arm movements is coupled with visual body information about an opponent.