The PSI theory is a theory of human action regulation by psychologist Dietrich Dörner [1, 2]. It is an attempt to create a body-mind link for virtual agents. It aims at the integration of cognitive processes, emotions and motivation. This theory is unique in such a way that emotions are not explicitly defined but emerges from modulation of perception, action-selection, planning and memory access. Emotions become apparent when the agents interact with the environment and display expressive behavior, resulting in a configuration that resembles emotional episodes in biological agents. The agents react to the environment by forming memories, expectations and immediate evaluations.
PSI agents possess a number of modulators and built-in motivators that lie within a range of intensities. These parameters combined to produce complex behavior that can be interpreted as being emotional. Additionally, by regulating these parameters, the agent is able to adapt itself to the different circumstances in the environment. This theory has been applied to different virtual agent simulations in different type of environments [3, 4, 5, 6, 7] and has proven to be a promising theory for creation of biologically plausible agents.
More information can be found at http://web.uni-bamberg.de/ppp/insttheopsy/ (In German but there are some papers in English). Some simulation software is also available for download from this site.
 Dörner, D.: The mathematics of emotions. In Frank Detje, D.D., Schaub, H., eds.:
Proceedings of the Fifth International Conference on Cognitive Modeling,
 Katrin Hille, A Theory on Emotion, http://web.uni-bamberg.de/ppp/insttheopsy/dokumente/Hille_A_theory_of_emotion.pdf
 D. Dörner and K. Hille. Articial souls: Motivated emotional robots. In Proceedings of the International Conference on Systems, Man and Cybernetics, pages 3828–3832, 1995.
 Bartl, C., Dörner, D.: Comparing
the behavior of psi with
human behavior in the biolab
game. In Ritter, F.E., Young, R.M., eds.: Proceedings of the Second
International Conference on Cognitive Modeling,
 Mei Yii Lim, Ruth Aylett & Christian Martyn Jones, Emergent Affective and Personality Model, The 5th International Working Conference on Intelligent Virtual Agents (IVA’05), LNAI 3661, Kos, Greece, September 12-14, 2005
 M.Y. Lim, R. Aylett & C.M. Jones, "Affective Guide with Attitude", Proceedings of the 1st International Conference on Affective Computing and Intelligent Interaction, Beijing, China, 22-24 October, 2005. http://www.macs.hw.ac.uk/~ruth/Papers/agents-affect/ACII05-mei.pdf
 Harald Schaub, Introduction and Delineation of the Investigation, June 2, 2004 http://web.uni-bamberg.de/ppp/insttheopsy/dokumente/Schaub_The_year_of_the_gardener._Behaviour_modelling_in_a_complex_situation._(Memo-MPG09).pdf