View - ResearchGate

Playing the Emotion Game with Feelix 71Figure 8.1.Left: Full-body view of Feelix. Right: Children guessing Feelix’s expressions.strategy 5 based on the level of emotion activation to select and display theemotional state of the robot.To define the “primitives” for each expression we have adopted the featuresconcerning positions of eyebrows and lips usually found in the literature,which can be described in terms of Action Units (AUs) using the Facial ActionCoding System [6]. However, the constraints imposed by the robot’s designand technology (see [3]) do not permit the exact reproduction of the AUs involvedin all of the expressions (e.g., inner brows cannot be raised in Feelix);in those cases, we adopted the best possible approximation to them, given ourconstraints. Feelix’s face is thus much closer to a caricature than to a realisticmodel of a human face.To elicit Feelix’s emotions through tactile stimulation, we have adopted thegeneric model postulated by Tomkins [12], which proposes three variants ofa single principle: (1) A sudden increase in the level of stimulation can activateboth positive (e.g., interest) and negative (e.g., startle, fear) emotions; (2)a sustained high level of stimulation (overstimulation) activates negative emotionssuch as distress or anger; and (3) a sudden stimulation decrease followinga high stimulation level only activates positive emotions such as joy. We havecomplemented Tomkins’ model with two more principles drawn from a homeostaticregulation approach to cover two cases that the original model did notaccount for: (4) A low stimulation level sustained over time produces negativeemotions such as sadness (understimulation); and (5) a moderate stimulationlevel produces positive emotions such as happiness (well-being). Feelix’s emotions,activated by tactile stimulation on the feet, are assigned different intensitiescalculated on the grounds of stimulation patterns designed on the aboveprinciples. To distinguish between different kinds of stimuli using only binarytouch sensors, we measure the duration and frequency of the presses applied