xviii
PREFACE
together with impressive demonstrations on problems like the cocktail-party effect,
where the individual speech waveforms are found from their mixtures. ICA became
one of the exciting new topics, both in the field of neural networks, especially unsu-
pervised learning, and more generally in advanced statistics and signal processing.
Reported real-world applications of ICA on biomedical signal processing, audio sig-
nal separation, telecommunications,fault diagnosis, feature extraction, financial time
series analysis, and data mining began to appear.
Many articles on ICA were published during the past 20 years in a large number
of journals and conference proceedings in the fields of signal processing, artificial
neural networks, statistics, informationtheory, and variousapplication fields. Several
special sessions and workshops on ICA have been arranged recently [70, 348], and
some edited collections of articles [315, 173, 150] as well as some monographs on
ICA, blind source separation, and related subjects [105, 267, 149] have appeared.
However, while highly useful for their intended readership, these existing texts typ-
ically concentrate on some selected aspects of the ICA methods only. In the brief
scientific papers and book chapters, mathematical and statistical preliminaries are
usually not included, which makes it very hard for a wider audience to gain full
understanding of this fairly technical topic.
A comprehensive and detailed text book has been missing, which would cover
boththemathematicalbackgroundand principles,algorithmicsolutions,and practical
applications of the present state of the art of ICA. The present book is intended to fill
that gap, serving as a fundamental introduction to ICA.
It is expected that the readership will be from a variety of disciplines, such
as statistics, signal processing, neural networks, applied mathematics, neural and
cognitive sciences, information theory, artificial intelligence, and engineering. Both
researchers, students, and practitioners will be able to use the book. We have made
everyeffortto make this book self-contained, so that a readerwith a basic background
in college calculus, matrix algebra, probability theory, and statistics will be able to
read it. This book is also suitable for a graduate level university course on ICA,
which is facilitated by the exercise problems and computer assignments given in
many chapters.
Scope and contents of this book
This book provides a comprehensive introduction to ICA as a statistical and compu-
tational technique. The emphasis is on the fundamental mathematical principles and
basic algorithms. Much of the material is based on the original research conducted
in the authors’ own research group, which is naturally reflected in the weighting of
the different topics. We give a wide coverage especially to those algorithms that are
scalable to large problems, that is, work even with a large number of observed vari-
ables and data points. These will be increasingly used in the near future when ICA
is extensively applied in practical real-world problems instead of the toy problems
or small pilot studies that have been predominant until recently. Respectively, some-