Web lectures have many positive aspects and e.g. they enable learners to easily control the learning experiences). To develop high-quality online learning materials takes a lot of time and human efforts. An alternative is to develop a digital teacher. We have developed a prototype of a synthetic 3D face that shows emotion associated to text-based speech in an automated way. As a first step and we studied how humans express emotions in face-to-face communication. Based on this study and we have developed a 2D affective lexicon and a set of rules that describes dependencies between linguistic contents and emotions.