This chapter presents a brief overview of Affective computing and a formal
definition of emotion given by various researchers. Human-computer interaction aims
to enhance communication between man and machine so that machines can acquire,
analyze, interpret and act on par with human beings. At the same time, Affective
human-computer interaction focuses on enhancing communication between man and
machines using affective information. Moreover, this chapter deals with Human
emotional expression and perception through various modalities such as speech, facial
expressions, physiological signals, etc. It also detailed the overview of Action Units
and Techniques for classifying facial expressions as reported in the literature.
Keywords: Action units, Affective computing, Affective HCI, Emotion expression, Facial expression, HCI.
