Kybernetes vol.34, nos. 1/2, 2005, pp. 6-14. Penultimate version.

Act always so as to increase the number of scientific perspectives: Introduction to the Heinz von Foerster volume

alexander riegler

CLEA, VUB, Krijgskundestraat 33, B-1160 Brussels
ariegler [at] vub.ac.be

His early years in multinational and multicultural pre-war Vienna are identified as a cause for Heinz von Foerster to acquire a transdisciplinary worldview that fueled many of his second-order cybernetic and constructivist insights, and served as source of inspiration for many of his colleagues and students. Furthermore, the contributions to the special issue on Heinz von Foerster are introduced and related to his work. The paper presents conclusions of what we can learn from his scientific convictions.

Key words. Transdisciplinarity; second order cybernetics; radical constructivism; cognition; quantum physics; society; philosophy.

The Person

Heinz von Foerster was born in 1911 into a city that was one of history’s most remarkable cultural and scientific melting pots before World War II: Vienna. It was the focus of a multinational and multicultural state, the Austro-Hungarian Empire, and was able to preserve its important role into the time between the wars after the empire was gone. Vienna gathered famous painters such as Gustav Klimt, and Egon Schiele, writers in the so-called “Literatencafés” such as Arthur Schnitzler and Hugo von Hofmannsthal, physicists such as Ernst Mach, Ludwig Boltzmann, and Erwin Schrödinger, psychoanalysists such as Sigmund Freud and Viktor Frankl, and last but not least philosophical authorities like the Vienna Circle and Ludwig Wittgenstein—the latter was a constant source of admiration and inspiration for Heinz von Foerster.

Heinz von Foerster had always been proud of being a Viennese. The city shaped his preference for boundless curiosity and a broad intellectual spectrum, which made him one of the most original, unorthodox and creative thinkers. He contributed to so many diverse scientific fields that it is impossible to relate him to a single discipline only. His work was inter- and transdisciplinary. Consequently, he liked to call himself as being “without discipline” despite his ingenious approach to many problems in cognition, artificial intelligence, information technology, demography, linguistic, management, education, logic, etc.

I don’t know where my expertise is; my expertise is no disciplines. I would recommend to drop disciplinarity wherever one can. Disciplines are an outgrowth of academia. In academia you appoint somebody and then in order to give him a name he must be a historian, a physicist, a chemist, a biologist, a biophysicist; he has to have a name. Here is a human being: Joe Smithhe suddenly has a label around the neck: biophysicist. Now he has to live up to that label and push away everything that is not biophysics; otherwise people will doubt that he is a biophysicist. If he’s talking to somebody about astronomy, they will say “I don’t know, you are not talking about your area of competence, you’re talking about astronomy, and there is the department of astronomy, those are the people over there,” and things of that sort. Disciplines are an aftereffect of the institutional situation. (Heinz von Foerster, quoted in Franchi, Güzeldere & Minch, this volume).

After WWII, Heinz von Foerster came into contact with the American scientific melting pot, most notably the meetings of the Josiah Macy foundation to discuss “circular-causal and feedback mechanisms in biological and social systems” (see, for example, Pias 2003). He was appointed the scientific editor of its transactions. In this function he humbly suggested to use the title of Norbert Wiener’s 1948 book “Cybernetics” as a label for the movement that was emanating from the meetings. Cybernetics was a genuine interdisciplinary endeavor. Among the participants of the meetings were neurologists (e.g., Warren McCulloch, Arturo Rosenblueth, Hans Lukas Teuber), psychiatrists (e.g., Ross Ashby), anthropologists (e.g., Gregory Bateson and Margaret Mead), mathematicians (e.g., Norbert Wiener, John von Neumann, and Walter Pitts), sociologists (e.g, Paul Lazarsfeld), and engineers (e.g., Claude Shannon, Julian Bigelow, and Foerster himself).

Later Heinz von Foerster would found his own interdisciplinary organization, the Biological Computer Laboratory (BCL) at the University of Illinois (e.g., M,ller 2000) to provide an environment for extensive collaboration among scientists (and artists) from various disciplines.[1] During its existence from 1958–1974, its aim was to transcend early first-order cybernetics “of observed systems” (Foerster 1973) in order to establish a second-order cybernetics “of observing systems.” He defined first-order cybernetics as the “epistemology for comprehending and stimulating biological processes as, e.g., homeostasis, habituation, adaptation, and other first-order regulatory processes. Second-Order Cybernetics provides a conceptual framework with sufficient richness to attack successfully such second-order processes as, e.g., cognition, dialogue, socio-cultural interactions, etc.” (Foerster 1973). Consequently, the observer-centered view of second order cybernetics served as a foundation for radical constructivism, which maintains that the cognitive apparatus brings forth the world out of experiences (Riegler 2001). Therefore, our understanding of what we are used to refer to as “reality” does not root in the discovery of absolute mind-independent structures but rather in “the operations by which we assemble our experiential world.” (Glasersfeld 1984).

As the main institution to investigate these and other second-order phenomena and problems, the BCL attracted a variety of researchers. Some of them were visiting professors, others were at the beginning of their scientific carreer or at the verge of starting one: William Ainsworth (England), Alex Andrew (England), W. Ross Ashby (England), Herbert Brün (Germany), Dan Cohen (Israel), Gotthard Günther (USA, Germany), Lars Löfgren (Schweden), Humberto Maturana (Chili), Gordon Pask (England), Stuart Umpleby (USA), Paul Weston (USA), to name but a few.[2]

Heinz von Foerster’s scientific career made him author and co-author of about 200 publications that reflect his transdisciplinary interests. Some of them have been reprinted in collections such as Foerster (1981, 1985, 1993a, 1993b, 2001, 2003). Many books and articles have been written about him as well. I refer the interested reader to the interview in this volume conducted by Franchi, Güzeldere & Minch and to the following biographies for further details of his life and career: Segal (1986/2001), Foerster, Müller & Müller (1997), Foerster & Pörksen (1998/2002), Grössing et al. (2001) (which includes a CDROM with audio files of Foerster’s “Stanford lecture” in 1983), Foerster & Bröcker (2002), Glanville (2003), and Pörksen (2003). “The Heinz von Foerster Page” (created in 1996) centralizes the access to various Heinz von Foerster-related documents on the worldwide web. It can be found at http://www.univie.ac.at/constructivism/HvF.html.

When Heinz von Foerster died on 2 October 2002 in his home on the “Rattlesnake Hill” in Pescadero, California, the world lost one of its most colorful and inspirative thinkers.

The contributions

The present volume of Kybernetes targets an interdisciplinary scientific audience. Authors were encouraged either to show the impact his ideas has had on their respective scientific work, to generate knowledge that draws upon his insights, or discussing future developments that emanate from his innovative ideas. The contributions are similar to his own papers in a technical sense: Not being afraid of formal methods and applying them in a modest and generally comprehensible way without slipping into a superficial treatment of popular topics. The purpose is to establish the Heinz von Foersterian world-view as an inspiring old and new perspective for the scientific community.

The contributions in this volume focus on various topics and methodology that were also central to Heinz von Foerster’s interests: Artificial neural networks, cognition, formal systems, quantum physics, social dimensions, and philosophy. This list in no way implies that the respective methodology used in any of the contributions was single-disciplinary. Rather, as the following summaries show, topics are interrelated.

The wide spectrum of his interests is also reflected in the interview that was carried out by Stefano Franchi, Güven Güzeldere, and Erich Minch in 1994. It presents in a concise form the stages in Foerster’s life and previews some of the research topics that are picked up by the contributors of this volume.

Artificial neural networks

Artificial neural networks were one of the “hot” topics at the BCL. They combine engineering (before the age of transistors, Foerster’s worked at the Electron Tube Lab) and empirical science (Foerster spent two “neurophysiological” sabbaticals at the respective research groups of Warren McCulloch and Arthuro Rosenblueth). As early as in 1960, the BCL developed a neural network prototype called “Numa-Rete,” which could count objects irrespective of their shape and size. Alex Andrew was one of the visiting professors at the BCL and personally involved in some of the neural network research there. His paper describes the activities of the BCL related to neural networks and self-organization in a broader historical context. Andrew draws the reader’s attention to the ill-defined nature of the term “self-organization” and stresses the relevance of “significance feedback” in multi-layer networks.

Having worked with a variant of neural networks, Timo Honkela suggests in his contribution that some of Foerster’s ideas have found a practical implementation in Tevo Kohonen’s method of unsupervised learning in an artificial neural network known as the “self-organizing map.” In particular the author suggests that a self-organizing map can be considered an example of a “non-trivial machine,” i.e., an automaton the output of which does not solely depend on the machine’s input. He mentions that this way of looking at it led to an application in information retrieval where exploration and search in huge collections of documents can be made easier by automatically organizing the collection as a Kohonen map.

Cognition

Beyond artificial neural networks, Heinz von Foerster had a general interest in cognition. One of his most prominent guest researchers at the BCL was Humberto Maturana for whom staying at the highly interdisciplinary place meant encouragement to continue developing his far-reaching framework based on the notion of autopoiesis. In this volume, Maturana gives an extensive review of his work and carries on to deal with “self-consciousness.” His point of departure are four Foersterian questions: What is more central, reality or understanding? Have solutions to the problem of “self-consciousness” to do with reality or with understanding? Can robots acquire self-consciousness? And what is the role of formalisms in biological explanations? Maturana has a very specific and concise way of writing. As Zeleny (1981) so aptly notes, his style reflects the organization of his thinking and does not intend to “beautify” it in any way that could endanger his intentions. Therefore, the reader new to Maturana will need to approach his text with great care, and becoming familiar with his basic notions (they are summarized in the appendix to Maturana’s paper) will greatly help one understand the author better. The reader is asked to read it thoroughly and consider notions and concepts in the context of others. As Zeleny says, Maturana’s writings demand “reflection on itself as whole, not an analysis of its components.”

My own contribution to this volume deals with the constructivist interpretation of human memory following Foerster’s postulate that cognition and memory must not be treated separately. Starting with the question of false memories and related memory distortions in cognitive psychology, I argue against the associative storageretrieval understanding of memory. Rather, memory from the radical constructivist point of view is inseparably embedded in cognitive processes. Drawing from psychological experiments related to childhood amnesia, I conclude that one of the most frequent objections to radical constructivism, namely that in case its theses were correct we would be able to construct anything we want, is just a feat of language that does not relate to the sensorimotor competences one acquired in early days.

The paper written by Bernd Porr and Florentin Wörgötter discusses the relations between Heinz von Foerster’s claim that the nervous system is operationally closed (i.e., it can interact only with its own states but not with the semantics of an outside world), linear signal/control theory, and animat research (i.e., dealing with biologically inspired autonomous agents). Using the mathematical formalism of linear control theory and emphasizing the agent’s ‘internal’ perspective, the implications of the operational closure of the nervous system and its equivalent in animats are analyzed. Furthermore, the concept of embodiment[3] is discussed from the perspective of radical constructivism: how can the nervous system identify inside and outside? The authors suggest this becomes possible for the organism as it learns a temporal correlation between reflex-loops established by different sensory inputs.

The importance of embodiment is further investigated by Tom Ziemke. The author relates the idea of situated cognition to Foerster’s work on operational closure. This is exemplified with a simple robot simulation model. The paper is a step forward to overcome the current over-simplifications of equating embodiment with simply being physically implemented, and will lead robotics researchers and others to re-examine von Foerster’s writings.

Formal Systems

A topic that had always gripped Heinz von Foerster’s attention was self-referentiality. This is noticeable in the titles of many of his publications, such as “cybernetics of cybernetics” (1974) and “understanding understanding” (2003), among others. In a formal context, he referred to it as the recursive application of an operation upon itself thereby creating stable eigenforms or tokens. Louis Kauffman explores the implications of eigenforms in a variety of contexts that lead to a new perspective on the relationship between the observer and the observed.

Alfred Inselberg, having been an early participant in the BCL and co-author of papers with Heinz von Foerster, is known as the inventor of the concept of parallel coordinates. In his contribution to this volume he summarizes many of the contributions he made to this method, which allows one to visualize and solve high-dimensional problems with computer algorithms. Since many of the projects at the BCL were of a complex nature themselves, such as knowledge, perception, and learning, the author refers to multidimensional geometry as the missing link of the BCL, a “toy” which many of the ambitious BCL projects relate to.

Quantum Physics

That an interdisciplinary approach leads to new solutions of old and obstinate problems is demonstrated by the two-part paper on “A theory of concepts and their combinations.” It attempts to account for the cognitive problem of how concepts join to form conjunctions and other more complex semantic compositions from a quantum-physical perspective. Heinz von Foerster’s educational background was physics, and his first monograph presented a quantum-mechanical model of memory. When quantum physicist Diederik Aerts met Heinz von Foerster at the Einstein Meets Margritte conference in Brussels he was immediately fascinated by his personality. So when teaming up with cognitive scientist Liane Gabora, together they recognized the potential of interdisciplinary research, which inspired Foerster almost 50 years ago to found the BCL. In their paper, the authors follow the intuition Foerster had in his monograph, namely that the mind and quantum mechanics have more in common than just using the same mathematical tools. In particular, they address two crucial problems in psychology: How to characterize concepts by means of their typical aspects, and how to formally describe the process of concept combination. The main idea is that concepts are contextually elicited since concepts interact with one another, therefore dynamically provoking a change of state of each interacting concept. In order to deliver a description of the combination of concepts, the authors introduce the “State Context Property Formalism,” which uses the same Hilbert-space operator algebra that is also applied to quantum mechanics. It accounts for the different states of concepts according to the contexts in which they are placed. In this perspective, a combination context selects for each involved concept its relevant aspects to be combined. By making the notion of context central to their model, the authors also claim to reconcile similarity-based approaches with explanation-based ones since an explanation constitutes a relevant context of its application rather than a typical description of a concept. Furthermore, the model was tested in a psychological experiment, which leaves few doubts that the application of quantum theory has an impact on concept research in psychology.

Another contribution that argues from a quantum physics point of view is Gerhard Grössing’s paper on “Observing Quantum Systems”. It focuses on a central notion of Heinz von Foerster, the distinction between trivial and non-trivial machines. The author arrives at the conclusion that the former corresponds to classical physics while the corresponding counterpart to non-trivial-machines are quantum systems. Emphasizing the importance of the well-known double slit experiment leading to non-locality, the author defends the de Broglie-Bohm formalism of quantum mechanics, i.e., the interpretation of quantum phenomena that, in contrast to the Copenhagen interpretation, preserves classical observables and determinism at the price of explicit non-locality. The author considers his article embedded in the wider framework of “quantum cybernetics,” which aims at modeling quantum systems in terms of circular causality. This makes it possible to depict waves and particles as mutually dependent system components yielding organizationally closed systems.

Social Dimensions

The intertwining of science and its application to society had increasingly become a topic in the BCL; it embarked on a chain of projects which gave priority to the social and cultural benefit emanating from scientific insights (Müller 2000). With the advent of the internet, the notion of knowledge has turned into one of big topics of modern information society. Inspired by Heinz von Foerster’s perspective on self-organization Christian Fuchs and Wolfgang Hofkirchner emphasize the fact that information-generating systems are self-organizing systems. The paper extends this close connection to the domain of social systems. Very much in the spirit of Foerster, who said that knowledge requires conscience (in German it is the corresponding German pun Wissen and Gewissen) the authors develop arguments that knowledge has ethical implications and that it implies responsibility.

How does the relationship between individual and society look like, what are the mechanisms through which they exert influence on each other? The contribution of Martin Schaurhofer and Markus Peschl is an earnest effort to relate “empowerment” to the work of Heinz von Foerster and the nature of personal change. Empowerment describes the processes of how to gain and increase autonomy and control in one’s own life. The authors emphasize the importance of the individual change in order to make a social change. For this, they refer to empowerment within knowledge management and show how these developments can contribute to the generation of a civil society that will be listened to in its demands. The resulting proposal is a model of knowledge management. It is based on four processes inspired by Foerster’s concept of a “cognitive element,” which represents a minimal case of a cognitive process: acquiring developing, representing knowledge, and sharing/distributing knowledge.

Philosophy

Last but certainly not least for Heinz von Foerster, two papers deal with philosophical concerns. Stuart Umpleby, having worked at the BCL himself, deals with the paradigm shift from the observed to the observing system in von Foerster’s second- order cybernetics. His paper describes some of the author’s personal experiences concerning different styles of thinking in continental Europe and the US/UK. In the light of these experiences, Umpleby proposes to make one further step in the Foersterian philosophy of science: from the observing system to the cultural context of the interaction between observed and observing system.

The final contribution written by Urban Kordeš wraps up Heinz von Foerster’s philosophy. It is a (personal) interpretation of his epistemological stance, a physicist’s attempt to present an up-to-date account of the impact of constructivist thinking in general and of Heinz von Foerster in particular, on the understanding of some basic concepts in epistemology. Such an undertaking is of great interest, given the current problems in scientific and philosophical thinking as it is evident in theoretical physics as well as in the continuing debates about the relationship between mind and brain. The author outlines a number of difficulties and suggestions for their solution, which were inspired Foerster and by others. He proceeds in a non-dogmatic way and with a good deal of self-doubt, which is a basic ingredient in constructivist thinking.

What can we learn from Heinz von Foerster?

The volume is meant to celebrate Heinz von Foerster’s scientific convictions. One of them was “The hard sciences are successful because they deal with the soft problems; the soft sciences are struggling because they deal with the hard problems,” which can be considered a consequence from his belief that “the more profound the problem that is ignored, the greater are the chances for fame and success.” (Foerster 1971). Clearly, he refers to the reductionist approach that has been applied in the exact and engineering sciences where problems are defined in a way that allows the researcher to decompose them in a linear fashion. In other domains, however, phenomena defy the reductionist worldview; they are characterized by their non-linearity where the sum of solutions to sub-problems does not yield a solution for the entire problem. While most of the authors in this volume are “hard scientists” (ranging from quantum physicists to biologists, and from mathematicians to computer scientists) none of them ignores the “profound problems” the way a reductionist would do.

However, there is a second aspect to Foerster’s criticism. In times of reassessing the scientific endeavor from the perspectives of postmodernism, pseudo- and anti-scientific movements, there should be no doubt about Foerster’s high demand on scientific rigor and integrity, and about his belief in the scientific method as a methodological tool that sharpens our understanding. However, he distinguished very well between the necessity of peer-reviews (being a cornerstone of the serious science) from a methodological perspective and the (sometimes unfortunate) aspect of abusing them to the advantage of the reviewer’s personal or political opinion. His early 1948 monograph was reviewed by no less a person than Erwin Schrödinger who did not “believe a word” of it but who declared the book free of errors from a mathematical point of view. Consequently, Heinz von Foerster appreciated very much the conclusion his publisher Deutieke drew from Schrödinger’s review report: “I don’t care what Schrödinger believes, I only want to know whether there is a mistake, and since there is no mistake I think we can print it.” (quoted in Franchi, Güzeldere & Minch, this volume).

Having been the head of the BCL for almost three decades, Foerster wanted to go beyond the traditional scientific practice to foster inter- and transdisciplinary approaches and to trigger further scientific developments based on the dialogue among researchers. This conviction is also reflected in the title of this editorial; it is a paraphrase on Heinz von Foerster’s often-quoted “ethical imperative”: “Act always so as to increase the number of choices.” Given the fact that most problems in science he was concerned with are undecidable in principle[4], it is the responsibility of the scientist to decide them. Therefore pluralistic perspectives on such problems can only be helpful to facilitate his or her decision.

The Reviewers

A journal that tries to honor the variety of research topics Heinz von Foerster was concerned with would not be possible without the help of many peer-reviewers. Therefore, I would like to thank the members of the review panel for their time and intellectual support, which provided helpful and constructive comments for the authors. In alphabetical order the external reviewers were: Sven Aerts, Stefan Artmann, Dirk Baecker, Peter Baumgartner, Marco Bettoni, Pille Bunnell, William Clancey, Gerard de Zeeuw, Olaf Diettrich, Dewey Dykstra Jr., Arne Engström, David Fass, Laleh Ghadakpour, Ernst von Glasersfeld, Brian Goodwin, Alessandro Guida, Yukio-Pegio Gunji, Inman Harvey, Vincent Kenny, Klaus Krippendorff, Fabien Mathy, Thomas Metzinger, John Mingers, Herbert F. J. Müller, Volker Müller-Benedict, Winfried Nöth, Paul Pangaro, Gerhard Schurz, Bernard Scott, Sverre Sjölander, John Stewart, Holger Theisel, Jean Paul Van Bendegem, Bernard Victorri, Manuela Viezzer, and Roberto Zarama.

Notes

  1. The attitude to approach complex phenomena from different disciplines, has caught on in many research organizations, such the Bielefelder Zentrum für interdisziplinäre Forschung in Germany (e.g., Kocka 1987), the widely-known Santa Fe-Institute in the US, and the (perhaps less famous) Konrad Lorenz-Institute in Austria and the Center Leo Apostel in Belgium.
  2. It is interesting to note that most of them had an European background.
  3. Embodiment refers to the argument that in order to account for cognition one has to take the organism’s structural coupling with its environment into consideration (Maturana & Varela 1980; Riegler 2002).
  4. Heinz von Foerster’s dictum “Only those questions which are in principle undecideable, we can decide” points to the fact that the solution to the “big problems” cannot be delegated to nature.

References

Foerster, H. von (1948) Das Gedächtnis. Eine quantenphysikalische Untersuchung. Wien: Franz Deuticke.

Foerster, H. von (ed.) (1974) Cybernetics of cybernetics, or the control of control and the communication of communication. University of Illinois. Republished in 1995 by Stephen A. Carlton with Future Systems in Minneapolis.

Foerster, H. von (1971) Responsibilities of competence. Journal of Cybernetics 2: 1–6. Reprinted in: Foerster, H. von (2003) Understanding understanding. NewYork: Springer, pp. 191–197.

Foerster, H. von (1981) Observing Systems. Seaside, CA: Intersystems Publications.

Foerster, H. von (1985) Sicht und Einsicht. Braunschweig: Vieweg.

Foerster, H. von (1993a) KybernEthik. Berlin: Merve-Verlag.

Foerster, H. von (1993b) Wissen und Gewissen. Frankfurt: Suhrkamp.

Foerster, H. von (2001) Short Cuts. Frankfurt: Zweitausendeins.

Foerster, H. von (2003) Understanding understanding. NewYork: Springer.

Foerster, H. von & Bröcker, M. (2002) Teil der Welt. Heidelberg: Carl-Auer-Systeme Verlag.

Foerster, H. von, Müller, A. & Müller, K. H. (1997) Der Anfang vom Himmel und Erde hat keinen Namen. Wien: Döcker. Republished in 2002 with Kulturverlag Kadmos in Berlin.

Foerster, H. von & Pörksen, B. (1998) Wahrheit ist die Erfindung eines Lügners. Heidelberg: Carl-Auer-Systeme Verlag. English translation: Foerster, H. von & Pörksen, B. (2002) Understanding Systems: Conversations on Epistemology and Ethics. New York: Kluwer/Plenum.

Franchi, S., Güzeldere, G. & Minch, E. (2004) From Vienna to California: A journey across disciplines. Interview Heinz von Foerster. This volume.

Glanville, R. (2003) Heinz von Foerster. Systems Research and Behavioral Science 20: 85–89.

Glasersfeld, E. von (1984) An introduction to radical constructivism. In: Watzlawick, P. (ed.) The invented reality: How do we know? New York: W. W. Norton, pp. 17–40.

Grössing, G., Hartmann, J., Korn, W. & Müller, A. (2001) Heinz von Foerster 90. Vienna: Edition Echoraum.

Kocka, J. (ed.) (1987) Interdisziplinarität. Frankfurt: Suhrkamp.

Maturana, H. R. & Varela, F. J. (1980) Autopoiesis and cognition: The realization of the living. Boston, Dordrecht: D. Reidel Publishing.

Müller, A. (2000) Eine kurze Geschichte des BCL. Österreichische Zeitschrift für Geschichtswissenschaften 11 (1): 9–30.

Pias, C. (ed.) Cybernetics – Kybernetik: The Macy-Conferences 1946–1953. Zürich: Diphanes.

Pörksen, B. (2003) Heinz von Foerster (1911–2002): The Socrates of cybernetics. International Journal of General Systems 32: 519–523.

Riegler, A. (2001) Towards a radical constructivist understanding of science. Foundations of Science, special issue on “The Impact of Radical Constructivism on Science” 6: 1–30.

Riegler, A. (2002) When is a cognitive system embodied? Cognitive Systems Research, special issue on “Situated and Embodied Cognition,” edited by T. Ziemke, 3: 339–348.

Segal, L. (1986) The Dream of Reality. Second edition. New York: Norton. An expanded version was published in 2001 with Springer in New York.

Wiener, N. (1948) Cybernetics of control and communication in the animal and the machine. New York: Wiley.

Zeleny, M. (ed.) (1981) Autopoiesis. A theory of living organization. Amsterdam: Elsvier North Holland.