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or left. The new information being generated by the pattern of spatial orbits took the form of sequences of numbers or symbols representing the sequence of labeled boxes. The complexity of these numeric or symbol sequences was then quantified in a variety of ways including the use of two fundamental measures of dynamical entropy.

One measure reflects how many new, previously unexplored boxes were entered by the rat per unit of time. This rate represents a percent of the possible. The second measure reflects how much of the time did the rat in each box visited as a distribution of the probable. The rate of expansion of the possible and the relative time in occupancy of these possibles, the probables, form the bases for the computation of these two kinds of entropies. For example, the work of Paulus and Geyer showed that the administration of a very small amount of stimulant drug, compared with a salt water control, led to an increase in the first measure of the number of new, previously unexplored, boxes entered per unit time. With respect to the second measure, the stimulant drug augmented exploratory activity was also more uniformly distributed over the possible boxes, making for more uniform probability. Administration of higher doses of stimulant drugs, at a critical dose, led suddenly to more spatially and temporally restricted and stereotyped patterns of motion of the rats, compulsive circling alternating with frozen sniffing. Both contributed to a decrease in the possible and nonuniformity in the distribution of the probabilities. In man, low doses of amphetamine tend to increase the rate and creativity of thought streams and high doses generate fixed ideas and paranoid delusions. In the statistical approach to nonlinear dynamical systems, time-dependent generation of new possibilities is called topological entropy, HT and the entropy associated with the distribution of probabilities is called the metric entropy, HM. These kinds of entropies have also been used to quantitate characteristic patterns of in human behavior as well.

We have previously mentioned these measures as used in human experiments by Karen Selz, a Research Professor of Psychiatry at Emory University in Atlanta. Recall that she devised a set of experiments leading to unobtrusive measures made on human subjects by asking them to remove, as many as they

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