Introduction and Historical Background
The occurrence of gastric secretion required direct stimulation (food); sham feeding of an eso-phagotomized dog also produced secretion, the secretion this time being obtained without actual stimulation of the stomach by food. Pavlov's behavioral observations were extremely accurate in their description, but his functional brain model and his hypothetical constructions were schematic in their form. The observation that mere sham feeding produced gastric secretion turned Pavlov's interest to what he termed "psychic secretion." Pavlov's procedure in studying and applying the conditional reflex phenomenon can be outlined in three stages (Konorski). In the first stage the "foundations" of the conditional reflex were laid down, beginning with the circumstances necessary for the formation of the conditional reflex. The second stage consisted of studies carried out to determine the dynamics of the cortical processes and mutual interrelations of positive and negative conditional reflexes. In the third and final stage the phenomena of functional pathology were studied and related to typological problems.