The aim of the book is to show how Kurt Lewin's classical topological system can be developed into a modern stochastic theory of psychology This theory builds, in terms of probabilities, on Lewin's main principles and also allows for predictions through computer simulations.

In Part One,some introductory examples are given to illustrate the simulation of the stochastic processes in psychology. The Lewinian system is then discussed along with suggestions for its modification and correction.

In Part Two, the 'stochastic field theory' is presented more systematically. The process of behavior is described as locomotion in a weighted graph, with the varying states of behavior corresponding to the vertices of the graph. The transition of the agent (individual) occurs in one step in discrete time, a) if the agent makes the trial and b) if the trial succeeds. The succes is determined by a particular success probability. The trial is preceeded by a kind of 'cognitive simulation' of the real choice situation. When this cognitive process is successful enough, the trial occurs. Thus, the behavior process is governed by three types of probabilities: 1) cognitive trial probabilities, 2) their success probabilities, and 3) the success probabilities of real trials (actions). Learning operators are applied to probabilities 1) and 2). The cognitive states and the 'real behavior states' are linked by particular correspondence probabilities. Central concepts in the Lewinian system - such as field, potency of field, valence, conflict, and tension - are redefined in terms of probabilities.

The assumption underlying the analysis of communication is that receiving a
message, interpreting it, and believing it produces dependence of behavior.
In formal presentation this means that conditional probabilities have to be
used for determining the cognitive process, the conditions being the messages
received. Norm sending and sanctions are analyzed in more detail.

Behavior on group level is analyzed by defining a particular space of 'group
states'.

In Part Three, the problems of operationalization are discussed and predictionsare
made by simulationg experiments in choice behavior in line with the theory.
Computer programs used in the simulation appear in forms of block diagrams and
lists in appendices.

In Chapter 3.5, the fundamental concepts used by Fritz Heider are quantified
and the principles of his balance theory are rewritten in terms of our stochastic
field theory. The process leading to balance is programmed and some results
from an experiment by Esch are estimated.

In the end, the stochastic field theory is compared with some Markov chain models, and, finally, some generalizations are briefly outlined.

**Keywords**: action, behavior, cognition, cognitive, communication, graph,
group, Heider, interaction, learning, Lewin, model, operator, probability, program,
simulation, sociometry, stochastic, theory.

*(The "Stochastic Field Theory of Behavior" is available in Tiedekirja,
Kirkkokatu 14, 00170 Helsinki, Finland.)*