The Towers of Silence
At the Institute of Experimental Medicine, founded in 1890, Ivan Pavlov explored the physiology of digestion. His work required precise measurements, free from outside influence. To achieve this, he constructed special sound-dampened laboratories known as the "Towers of Silence." These isolated chambers allowed his team to conduct experiments in a controlled environment, eliminating stray sounds or movements that could accidentally trigger a response in the canine subjects.
Inside, the apparatus was both simple and invasive. Dogs were held in a harness to keep them stationary. To measure salivation, Pavlov's team performed a minor surgery to create a fistula, or opening, in the dog's cheek or esophagus. A tube was attached to this opening, channeling the saliva into a measuring device that recorded the number of drops. The unconditioned stimulus was typically a meat powder, which reliably caused salivation. The neutral stimuli varied; while the bell is well-known, Pavlov more frequently used metronomes, buzzers, and lights because their properties could be precisely controlled.
Psychic Secretions
Pavlov did not originally intend to study psychology. He was a physiologist who won the Nobel Prize in 1904 for his research on the digestive system. During these experiments in the 1890s, he noticed that experienced dogs began to salivate before food was presented. The sight of the food dish, or even the sound of the lab assistant's footsteps, was enough to start the flow of saliva. Pavlov called this phenomenon "psychic secretion."
This accidental observation shifted his focus. He began systematically pairing a neutral stimulus, like the ticking of a metronome, with the presentation of food. After several repetitions, the dog's brain associated the two events. Soon, the metronome's ticking alone was enough to trigger salivation, even with no food in sight. The neutral stimulus had become a conditioned stimulus, and the salivation a conditioned response. This process, which Pavlov termed classical conditioning, showed a basic mechanism of learning in the brain. It showed how automatic, reflexive behaviors could be triggered by new, previously unrelated stimuli through association.