The sensory nature of reward in instrumental behavior.

Improvement in the sensory state, or "better-being," achieved either through obtaining desirable sensations or through escaping undesirable sensations, is considered the essential value which maintains the instrumental behavior. This value may vary depending on such factors as the intensity of the stimulus producing sensations, the effects of its previous occurrence, and the changes in the internal and external environment. Methods of evaluation of sensory "better-being" by means of measuring instrumental, autonomic and EEG responses are discussed.