From the machine to the ghost within: Pavlov's transition from digestive physiology to conditional reflexes

I. P. Pavlov's transition from research on digestive physiology to investigations of conditional reflexes involved related departures from two firmly established traditions in his laboratory. One was conceptual: The standardized line of investigation that Pavlov had applied fruitfully to the gastric and pancreatic glands proved inapplicable to the salivary glands, leading him to reevaluate his approach to "psychic secretion." The dynamics and nature of this reevaluation owed much to a second departure, this one from a standard laboratory practice: Confronted with a conceptual problem that he recognized as psychological and, therefore, beyond his expertise, Pavlov recruited outside experts to help him resolve it, thus importing perspectives from contemporary psychology and psychiatry. The important role of insights from these two disciplines in the birth of research on conditional reflexes has been obscured by Pavlov's tale about this episode - a tale repeated uncritically by subsequent commentators. The intellectual terms of Pavlov's transition are evident in the phrase he chose to replace "psychic secretion" - "uslovnyi refleks." This term is commonly translated into English as "conditioned reflex," but its original meaning for Pavlov is better translated as "conditional reflex."