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THE SIGHT OF TASTY FOOD MAKES A HUNGRY MAN’S MOUTH WATER

   Many of the key discoveries made when modern psychology was still in its infancy were the result of research by scientists working in other fields. Ivan Pavlov, a Russian physiologist, is one of the best known of these early pioneers, whose investigations into the secretion(分泌) of saliva(唾液) during digestion in dogs led him to some unexpected conclusions.

   During the 1890s, Pavlov carried out a series of experiments on dogs, using various surgically implanted(植入的) devices to measure the flow of saliva when these animals were being fed.He noted that the dogs salivated(分泌唾液) not only when they were actually eating, but also whenever they could just smell or see some appetizing(引起食欲的) food.

   The dogs would even salivate, in anticipation of food being produced, when they were simply being approached by one of their keepers.Pavlov’s observations led him to investigate the links between various stimuli and the responses they elicited.In one experiment, he set off a clicking metronome(节拍器) just before offering food to the dogs, repeating this process until the animals always associated the sound with a good meal.

   This “conditioning” eventually resulted in the dogs salivating in response to the click of the metronome alone.In further experiments, Pavlov replaced the metronome with a bell or buzzer, a flashing light, and whistles of different pitches.

   However, regardless of the nature of the stimulus used, the result was the always same: once an association between the neutral stimulus (bell, buzzer, or light) and food had been established, the dogs would respond to the stimulus by salivating.

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"Facts are the air of science. Without them a man of science can never rise."
                     ——Ivan Pavlov

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   Pavlov’s dogs would salivate simply at the sight of someone in a white lab coat.They had become “conditioned” to associate the coat with eating, as whoever fed them always wore one.

Conditioned response

   Pavlov concluded that the food offered to the dogs was an “unconditioned stimulus” (US), because it led to an unlearned, or “unconditioned” response (UR) – in this case, salivation.The click of the metronome, however, only became a stimulus to salivation after its association with food had been learned.Pavlov then called this a “conditioned stimulus” (CS).The salivation in response to the metronome was also learned, so was a “conditioned response” (CR).

   In later experiments, Pavlov showed that conditioned responses could be repressed, or “unlearned”, if the conditioned stimulus was given repeatedly without being followed by food. He also demonstrated that a conditioned response could be mental as well as physical, by carrying out experiments in which various stimuli were associated with pain or some form of threat and began to elicit a conditioned response of fear or anxiety.

   The principle of what is now known as classical or Pavlovian conditioning, as well as Pavlov’s experimental method, marked a ground-breaking step in the emergence of psychology as a truly scientific, rather than philosophical, discipline.Pavlov’s work was to be hugely influential, particularly on US behaviourist psychologists, such as John B. Watson and B.F. Skinner.

MORE TO KNOW…

APPROACH

Classical conditioning

BEFORE

• Early 12th century Arab physician Avenzoar (Ibn Zuhr) performs experiments on animals in order to test surgical procedures.
• 1890 In Principles of Psychology, William James states that in animals “the feeling of having executed one impulsive step is an indispensable part of the stimulus of the next one”.

AFTER

• 1920 John B. Watson’s “Little Albert” experiment demonstrates classical conditioning in humans.

• 1930s B.F. Skinner shows that rats can be “conditioned” to behave in a specific way.

• 1950s Psychotherapists employ “conditioning” as part of behaviour therapy.

IVAN PAVLOV

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   Ivan Pavlov, the eldest son of a village priest in Ryazan, Russia, was initially destined to follow in his father’s footsteps.However, he quickly abandoned his training at a local seminary, transferring to the University of St Petersburg to study natural science.After graduation in 1875, he enrolled at the Academy of Medical Surgery, where he gained a doctorate(博士学位) and later a fellowship.

   In 1890, Pavlov became a professor at the Military Medical Academy, and was also made director of the physiology department at the Institute of Experimental Medicine.It was here that he carried out his famous research into the digestive(消化的)secretions(分泌物) of dogs, which won him the Nobel Prize in 1904.Pavlov retired officially in 1925, but continued his experiments until his death from pneumonia(肺炎) in February 1936.

Key works

• 1897 Lectures on the Work of the Principal Digestive Glands
• 1928 Lectures on Conditioned Reflexes(条件反射)
• 1941 Conditioned Reflexes and Psychiatry