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200 WALTER R. STAHL

tempted to explain data in human coordinationdisturbances (Parkinson’s disease) on the basis of a discrete cerebellar control theory; Braynes and Svechinskiy (1964) presented a generał Computer model of adaptive neuromuscular control. Performance scores would clearly be the appro-priate invariants for these cases.

Conditioned reflex mechanisms are also the subject of a number of modeling studies. A mathematical representation of excitation-inhibi-tion phenomena during formation of conditioned reflexes has been provided by Savinov et dl. (1962,1964), with the use of a complex electro-analog model. Vodovnik (1965) has simulated Pavlovian conditioned-reflex formation by a specialized digital Computer programming tech-niąue (Logical Programming Language of Lyapunov) and is able to obtain a reasonable qualitative (relational) Computer model. Conditioned reflex models are also described in a book on automata models of organ-isms by Gaaze-Rapoport (1961). Many similar reports by Russian authors could be cited. The similarity criteria for conditioned reflex models are usually of the relational variety, with numerical invariants (intensity of excitation and inhibition, timing problems) entering as important secondary conditions.

A large gap clearly exists at present between the phenomenological, neurophysiological, and molecular-cellular models, but this need not imply that neurophysiological modeling has not been successful. A “complete” model extending from the biochemical-genetic Ievel to the purely phenomenological one of observable behavior is imaginable, but would probably be too complex to be useful. Various kinds of compro-mises on ovei-all system representation are possible. In his book “A Model of the Brain,” J. Z. Young (1964) uses “nerve circuit theory” to represent observable brain anatomy and to explain with considerable success the behavior of the octopus. Guzman-Flores et al. (1963) attempt to integrate known neuron net models with observed electrophysiological data for simple spinał reflexes in the cat. The criteria for this model might include numerical ones based on probability and information theory.

C. Visual System Models

A considerable number of reports pertain specifically to the visual system. Estes and Taylor (1964) have described a model in which in-formation theory is used to analyze responses of the human eye when presented With very brief visual exposures, whereas Sokolov (1960) has considered the informational condensation processes taking place during