a qualitatively unique form of higher nervous activity peculiar to man; a system of speech signals (pronounceable, audible, and visible). This concept was set forth by I. P. Pavlov (1932) to define the fundamental differences in brain function between animals and man. The animal brain reacts only to direct visual, acoustic, and other stimuli or their traces, and the resulting sensations constitute the first signaling system. Man, however, possesses in addition to the first signaling system the ability to generalize with words the countless signals of this system. In so doing, a word, as Pavlov put it, becomes a signal of signals. The analysis and synthesis performed by the cerebral cortex when a second signaling system is present relate not only to individual, concrete stimuli but also to their generalization in the form of words. The second signaling system arose in the course of evolution during social activity. The capacity for the generalized reflection of phenomena and objects provided man with an unlimited ability to orient himself in the surrounding world and enabled him to create science.

The first and second signaling systems represent different levels of a unified higher nervous activity, but the second signaling system is more important. It came into being solely under the influence of man’s dealings with other people—that is, it was determined not only by biological factors but also by social ones. The nature of the interaction of the two systems may vary with the individual’s educational level (social factor) and characteristics of his nervous system (biological factor). Some people have a relatively weak first signaling system; their direct sensations are dull and weak (intellectual types). Others, in contrast, receive the signals of the first signaling system clearly and strongly (artistic types). The timely and correct development of both signaling systems are needed for the sound development of the personality.

In the study of the second signaling system there was an initial emphasis on the accumulation of facts detailing the significance of the generalization function of verbal signals. Subsequently, an emphasis developed on the discovery of neural mechanisms involved in verbal activity. It has been determined that the process of generalization by means of words develops as a result of the elaboration of a system of conditioned associations; in this system the nature of the associations and their number are important: associations that are worked out during childhood facilitate the generalization process. Verbal signals produce persisting changes in excitability and stronger, more frequent, and longer electrical discharges in the nerve cells in certain regions of the cerebral cortex. The second signaling system developed as a result of the activity of the entire cerebral cortex; it is impossible to link this process to the function of any one individual portion of the brain.