The Tower of Silence

To prove that a simple signal could trigger a dog's salivation, Ivan Pavlov had to eliminate everything else. He built a laboratory so perfectly isolated it was nicknamed the "tower of silence."

Studying digestion—which earned him the Nobel Prize in 1904—Pavlov noticed that his dogs salivated even before receiving food, at the mere sound of the caretaker's footsteps. He saw a "conditioned reflex": a neutral stimulus, associated with food, eventually triggered the response alone. To prove that a simple signal could trigger a dog's salivation, Ivan Pavlov had to eliminate everything else.

To measure the phenomenon without polluting it, he had a building constructed in Petrograd with thick walls, sealed windows, and foundations isolated from vibrations. Each dog was isolated there, signals delivered remotely by the experimenter, out of sight. He built a laboratory so perfectly isolated it was nicknamed the "tower of silence."

This extreme device embodied an ambition: to transform psychology into an exact science, where every variable is controlled. Pavlovian conditioning would become one of the cornerstones of behaviorism and our understanding of learning.