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72 Socially Intelligent Agentsto the feet. The type of stimuli are calculated on the basis of a minimal timeunit or chunk. When a chunk ends, information about stimuli—their numberand type—is analyzed and the different emotions are assigned intensity levelsaccording to the various stimulation patterns in our emotion activation model.The emotion with the highest intensity defines the emotional state and expressionof the robot. This model of emotion activation is implemented by meansof a timed finite state machine described in [3].3. Playing with FeelixTwo aspects of Feelix’s emotions have been investigated: the understandabilityof its facial expressions, and the suitability of the interaction patterns.Emotion recognition tests 6 , detailed in [3], are based on subjects’ judgmentsof emotions expressed by faces, both in movement (the robot’s face) and still(pictures of humans). Our results are congruent with findings about recognitionof human emotional expressions reported in the literature (e.g., [5]). Theyshow that the “core” basic emotions of anger, happiness, and sadness are mosteasily recognized, whereas fear was mostly interpreted as anxiety, sadness, orsurprise. This latter result also confirms studies of emotion recognition frompictures of human faces, and we believe it might be due to structural similaritiesamong those emotional expressions (i.e. shared AUs) or/and to theneed of additional expressive features. Interestingly, children were better thanadults at recognizing emotional expressions in Feelix’s caricaturized face whenthey could freely describe the emotion they observed, whereas they performedworse when given a list of descriptors to choose from. Contrary to our initialguess, providing a list of descriptors diminished recognition performance formost emotions both in adults and in children.The plausibility of the interactions with Feelix has been informally assessedby observing and interviewing the same people spontaneously interacting withthe robot. Some activation patterns (those of happiness and sadness) seem to bevery natural and easy to understand, while others present more difficulty (e.g.,it takes more time to learn to distinguish between the patterns that activate surpriseand fear, and between those that produce fear and anger). Some interesting“mimicry” and “empathy” phenomena were also found. In people tryingto elicit an emotion from Feelix, we observed their mirroring—in their ownfaces and in the way they pressed the feet—the emotion they wanted to elicit(e.g., displaying an angry face and pressing the feet with much strength whiletrying to elicit anger). We have also observed people reproducing Feelix’sfacial expressions during emotion recognition, this time with the reported purposeof using proprioception of facial muscle position to assess the emotionobserved. During recognition also, people very often mimicked Feelix’s ex-