The Role of Nonlinear Dynamics in Affective Valence and Arousal Recognition

This paper reports on a new methodology for the automatic assessment of emotional responses. More specifically, emotions are elicited in agreement with a bi-dimensional spatial localization of affective states. i.e. arousal and valence dimensions. A dedicated experimental protocol was designed and realized where specific affective states are suitably induced while three peripheral physiological signals, i.e. ElectroCardioGram (ECG), ElectroDermal Response (EDR), and ReSPiration activity (RSP), are simultaneously acquired. A group of 35 volunteers was presented with sets of images gathered from the International Affective Picture System (IAPS) having five levels of arousal and five levels of valence, including both a neutral reference level. Standard methods as well as non-linear dynamic techniques were used to extract sets of features from the collected signals. The goal of this paper is to implement an automatic multi-class arousal/valence classifier comparing performance when extracted features from non-linear methods are used as alternative to standard features. Results show that, when non-linearly extracted features are used, the percentages of successful recognition dramatically increase. A good recognition accuracy (>90%) after 40-fold cross-validation steps for both arousal and valence classes was achieved by using the Quadratic Discriminant Classifier (QDC).