This work has been carried out in the Neural Networks Research Centre, Helsinki University of Technology, during 1993-1997. I wish to thank Academy Professor Teuvo Kohonen for guidance and being the supervisor of the thesis and providing all the excellent facilities and financial support. His contribution has also been substantial to the whole research field around this work.
I wish to thank all the personnel of the Neural Networks Research Centre and the Laboratory of Computer and Information Science for creating a pleasant and productive working atmosphere. Special thanks for comments on the manuscript are due to Professor Erkki Oja and Dr. Samuel Kaski. I would also like to thank Dr. Jorma Laaksonen and Dr. Samuel Kaski for valuable aid in managing the incomparable document preparation system used for making all the publications and this thesis.
The financial support of the Academy of Finland as well as the Foundation for the Promotion of Technology and Emil Aaltonen Foundation is gratefully acknowledged.