Which role do computer models play for the psychological research on emotions ? This question is not new, but some of the recent answers are. Since 1988, when Pfeifer published an overview of the available literature, the number of approaches to this question has been principally unchanged; however, the depth of these approaches has changed considerably.
In his article "Artificial Intelligence Models of Emotions" (1988) Pfeifer did not only try to give an overview of the existing modeling approaches, he also classified them into two main categories:
a) Augmented Cognitive Models
Approaches in this category do not have emotions at their center, but predominantly consist of models for cognitive processes, during which emotions play a "supplementing" role. Typical of these models is that they are concerned with a well-defined task to which emotions are added as an auxiliary factor.
b) AI Models of Emotion
Approaches in this category place the modelling of emotions into the center. For such models the basic assumption of a complex environment is typical, in which clear problem descriptions can be realized only with difficulty.
In a further work, Pfeifer (1994) modified this classification. He now differentiates between "reasoners" and "psychological models". Reasoners are models which are based on specific taxonomies of emotions and have the task to classify them. Psychological models are models whose goal it is to model emotional processes per se.
The following work tries to cover those approaches as well as others which cannot be classified into one or the other of those categories. Therefore, my classification differs from Pfeifer's. Computer models of emotions are classified according to their objectives:
a) computers, who "understand" and "express" emotions and
b) computers that "have" emotions.
It is this latter category which is of particular interest for the psychological research into emotions, although it raises the most epistemological questions. Approaches of the first category consist simply of more or less refined models of existing theories of emotions and pose, therefore, mainly technical problems. But developing computers that possess emotions means initiating an evolutionary process which eventually will lead to the emergence of an emotional sub-system independent from its human creators.
This work will be concerned, therefore, primarily with approaches of the second category and will present them in their historical and theoretical context. Technical explanations which are necessary for the understanding of the technical implementation of the respective models, will be discussed as briefly as possible.
After an introductory overview (chapter 2) I deal shortly with the epistemological dimensions of computer modelling of emotions (chapter 3). I then present a short overview of the psychological theories of emotions which serve as a basis for computer models of emotions (chapter 4). Short descriptions of some of the most important models of the first category follow (chapter 5). The main part of the work is occupied with models of the second category,beginning with the works of Simon (Chapter 6) and Toda (chapter 7) as well as describing a first implementation of Toda's model (chapter 8). The next two chapters describe the works of Sloman (chapter 9) and Wright (chapter 10), whose model follows directly from Sloman's theories. Toda's approach has recently inspired many researchers to build emotional autonomous agents, some of which are described here (chapter 11). A final chapter (chapter 12) discusses the importance of the models described in this work for the psychological research into emotions.
This work is a thesis which I wrote in 1998 in order to obtain a diploma in psychology. My supervisors were Wulf-Uwe Meyer and Rainer Reisenzein, both from the University of Bielefeld. I am indebted to both of them because they not only provided me with the opportunity to finish my studies after an interruption of 20 years, but because they again ignited my interest into the psychology of emotions. Furthermore, they provided me with a lot of valuable suggestions.