11:15   Oral Session 2-KZ – Robots & Artificial Agents 2
Chair: Ana Paiva
25 mins
The Effect of Color on Expression of Joy and Sadness in Virtual Humans
Celso Miguel de Melo, Jonathan Gratch
Abstract: For centuries artists have been exploring color to express emotions. Following this insight, the paper describes an approach to learn how to use color to influence the perception of emotions in virtual humans. First, a model of lighting and filters inspired on the visual arts is integrated with a virtual human platform to manipulate color. Next, an evolutionary model, based on genetic algorithms, is created to evolve mappings between emotions and lighting and filter parameters. A first study is, then, conducted where subjects evolve mappings for joy and sadness without being aware of the evolutionary model. In a second study, the features which characterize the mappings are analyzed. Results show that virtual human images of joy tend to be brighter, more saturated and have more colors than images of sadness. The paper discusses the relevance of the results for the fields of expression of emotions and virtual humans.
25 mins
There’s Always Hope: Enhancing Agent Believability through Expectation-Based Emotions
Tibor Bosse, Edwin Zwanenburg
Abstract: To endow virtual agents with more realistic affective behavior, the notion of expectation-based emotions plays an important role: emotional states of agents should not only be triggered by present stimuli, but also by anticipation on future stimuli, and evaluation of past stimuli in the context of these anticipations. Within this study, an extension of the BDI-model with expectation-based emotions is proposed. The model has been implemented in the modeling language LEADSTO. In addition, a game application has been developed, in which a user can play a dice game against an agent that is equipped with the emotion-based model. An empirical evaluation indicates that the model significantly enhances the agent’s believability, in particular with respect to its involvement in the situation.
25 mins
Pleasure-Arousal-Dominance Driven Facial Expression Simulation
Hana Boukricha, Ipke Wachsmuth, Andrea Hofstätter, Karl Grammer
Abstract: Expressing and recognizing affective states with respect to facial expressions is an important aspect in perceiving virtual humans as more natural and believable. Based on the results of an empirical study a system for simulating emotional facial expressions for a virtual human has been evolved. This system consists of two parts: (1) a control architecture for simulating emotional facial expressions with respect to Pleasure, Arousal, and Dominance (PAD) values, (2) an expressive output component for animating the virtual human's facial muscle actions called Action Units (AUs), modeled following the Facial Action Coding System (FACS). A large Face Repertoire (FR) of about 6000 faces arranged in PAD-space with respect to two dominance values (dominant vs. submissive) is obtained as a result of the empirical study. Using the FR an approach towards realizing facial mimicry for a virtual human based on backward mapping AUs displaying an emotional facial expression on PAD-values is outlined. A preliminary evaluation of this first approach is realized with AUs corresponding to the basic emotions Happy and Angry.