In these essays Heinz von Foerster discusses some of the fundamental principles that govern how we know the world and how we process the information from which we derive that knowledge. Included are path- breaking articles concerning the principles of computation in neural nets (1967), the definition of self-organizing systems (1960), the nature of cognition (1970), as well as recent expansions on these themes (e.g. "How recursive is communication," 1993). Working with Norbert Wiener, Warren McCullough, and others in the 1960s and 1970s, von Foerster was one of the founders of the science of cybernetics, which has had profound effects both on modern systems theory and on the philosophy of cognition. At the Biological Computer Laboratory at the University of Illinois he produced the first parallel computers and contributed to many other developments in the theory of computation and cognition.

The book treats two approaches to decision theory: (1) the normative, purporting to determine how a 'perfectly rational' actor ought to choose among available alternatives; (2) the descriptive, based on observations of how people actually choose in real life and in laboratory experiments. The mathematical tools used in the normative approach range from elementary algebra to matrix and differential equations. Sections on different levels can be studied independently. Special emphasis is made on 'offshoots' of both theories to cognitive psychology, theoretical biology, and philosophy.

Fifty years ago when Jacques Hadamard set out to explore how mathematicians invent new ideas, he considered the creative experiences of some of the greatest thinkers of his generation, such as George Polya, Claude Lévi-Strauss, and Albert Einstein. It appeared that inspiration could strike anytime, particularly after an individual had worked hard on a problem for days and then turned attention to another activity. In exploring this phenomenon, Hadamard produced one of the most famous and cogent cases for the existence of unconscious mental processes in mathematical invention and other forms of creativity. Written before the explosion of research in computers and cognitive science, his book, originally titled The Psychology of Invention in the Mathematical Field , remains an important tool for exploring the increasingly complex problem of mental life. The roots of creativity for Hadamard lie not in consciousness, but in the long unconscious work of incubation, and in the unconscious aesthetic selection of ideas that thereby pass into consciousness. His discussion of this process comprises a wide range of topics, including the use of mental images or symbols, visualized or auditory words, "meaningless" words, logic, and intuition. Among the important documents collected is a letter from Albert Einstein analyzing his own mechanism of thought.

Mental Chronometry (MC) comprises a variety of techniques for measuring the speed with which the brain processes information. First developed in mid-1800, MC was subsequently eclipsed by more complex and practically useful types of psychometric tests stemming from Alfred Binet. This class of mental tests, however, has no true metric relating the test scores to any specific properties of the brain per se. The scores merely represent an ordinal scale, only ranking individuals according to their overall performance on a variety of complex mental tasks. The resulting scores represent no more than ranks rather than being a true metrical scale of any specific dimension of brain function. Such an ordinal scale, which merely ranks individuals in some defined population, possesses no true scale properties, possessing neither a true zero or equal intervals throughout the scale. This deficiency obstructs the development of a true natural science of mental ability. The present burgeoning interest in understanding individual differences in mental abilities in terms of the natural sciences, biology and the brain sciences in particular, demands direct measures that functionally link brain and behavior. One such natural ratio scale is time itself - the time it takes the brain to perform some elementary cognitive task, measured in milliseconds. After more than 25 years researching MC, Jensen here presents results on an absolute scale showing times for intake of visual and auditory information, for accessing short-term and long-term memory, and other cognitive skills, as a function of age, at yearly intervals from 3 to 80 years. The possible uses of MC in neurological diagnosis and the monitoring of drug effects on cognition, the chronometric study of special time-sensitive talents such as musical performance, and presents a theory of general intelligence, or g, as a function of the rate of oscillation of neural action potentials as