Pavlov conducted research on the secretion of gastric juice. Whenever food enters the stomach, a large amount of gastric juice is released to aid in digestion. Pavlov experimented on dogs to understand how the brain communicates commands to the stomach.
One day, Pavlov and his assistant conducted gastric secretion experiments on an elderly dog that had been domesticated for many years. This dog had lived in the laboratory for a long time and was familiar with all the staff members conducting the experiments. Dogs are very perceptive to human behavior; the staff fed them daily, so the dogs recognized their caregivers.
The elderly dog mentioned was quite intelligent and knew Pavlov was in charge, so it showed a lot of affection towards him. The dog was placed on a testing platform, where gastric juice dripped out and was collected in a tray through a tube. The laboratory was so quiet that you could hear the soft sound of breathing. An hour passed, during which the staff observed and recorded the data. The dog’s gastric juice secretion was normal, approximately 25 drops per minute.
Suddenly, the sound of footsteps from the dog caregiver echoed outside the door, followed by the caregiver passing by the laboratory with the dog’s food, the footsteps fading away.
At that moment, the experimenters noticed a spike in the dog’s gastric juice secretion, increasing to about 100 drops per minute. This phenomenon had never occurred before, and the laboratory staff looked around in surprise but did not see anything unusual. They decided to call Pavlov to report this strange occurrence. Upon hearing this, Pavlov was very surprised; he carefully observed the laboratory again but did not detect anything out of the ordinary. From that moment on, he became absorbed in thought.
While everyone was pondering and trying to figure out the cause, they heard the footsteps of the dog caregiver approaching again, as he had just finished feeding the dog. When the caregiver walked by the door with the food, Pavlov and the laboratory staff noticed that the dog’s gastric secretion significantly increased once more. The experimenters suddenly realized and told Pavlov that the previous increase in gastric secretion was due to the caregiver passing by the door.
Pavlov pondered whether the dog’s increased gastric secretion was somehow linked to the caregiver’s footsteps. To confirm this, Pavlov instructed the dog caregiver to walk by the laboratory door every 15 minutes, repeating this three times.
The dog caregiver found Pavlov’s request unusual but followed it nonetheless. Pavlov and the experimenters were excited to discover that each time the caregiver walked past the laboratory door, the dog’s gastric secretion spiked. Pavlov concluded, “The sound of the caregiver’s footsteps is associated with the arrival of food; over time, a special connection forms in the dog’s mind, meaning the caregiver’s footsteps can replace the food itself. When the footsteps are heard, the dog anticipates food will soon be provided and the brain signals the stomach to produce more gastric juice.”
From this discovery, Pavlov theorized that any type of signal, such as a bell, light, or whistle, could also elicit a similar response as long as it was consistently associated with the arrival of food over time.
The next day, Pavlov instructed the dog caregiver to ring a bell before bringing the food. After one month, this training yielded preliminary results, much to the delight of many observers. They came to see that at feeding time, simply ringing the bell would cause all the dogs to excitedly rush to their feeding troughs, eagerly awaiting their meal.
However, this experiment only worked with the dogs that had been trained for a long time; it did not apply to newly born or untrained dogs. Pavlov believed this was a type of response to external stimuli, which he termed “conditional reflex” in animals.
Later, Pavlov delved deeper into these issues and wrote his famous works. For these achievements, Pavlov was awarded the Nobel Prize. He recognized that science is infinite, and he must continue to strive tirelessly for its advancement.
“Science demands that each individual possess a spirit of utmost diligence and great enthusiasm“.
— Pavlov —
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