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Narrator: Behavioral psychologists have[br]come up with new views,

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not only of animal behavior, [br]but of human nature as well.

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And these views all concern a process[br]that we take for granted: learning.

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Because we are all truly born to learn.

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Ironically, one of the most important figures[br]in the study of learning, Ivan Pavlov,

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wasn't concerned with the subject at all.

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At least, not at first.

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Pavlov, a noted Russian scientist,

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won the Nobel Prize for Physiology[br]and Medicine in 1904.

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As this original footage shows, Pavlov [br]was initially interested in digestion

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and the action of the salivary glands.

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By diverting the saliva of dogs into test[br]tubes, he could precisely measure

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if and how much they salivated[br]during digestion.

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When food was presented,[br]the dog salivated quickly,

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an inherited salivary reflex.

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But over repeated testings,[br]a strange thing happened.

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The dog salivated[br]before contact with the food.

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Just the sight of the food was enough[br]to stimulate their drooling.

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Then, just seeing the food dish, or even[br]hearing the footsteps of Pavlov or his assistants,

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was enough to trigger this built-in reflex.

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What was going on to elicit this response?

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Pavlov decided to find out,[br]by systematically varying the stimuli

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and measuring the dogs' reaction.

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[Metronome clicking]

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Metronomes, lights, and bells[br]were all used as stimuli,

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and they all worked as stand-ins for[br]the food.

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What mattered was not the kind of[br]stimulus that was used,

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but the fact that it reliably signaled[br]that food was on the way.

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♫ Electronic Music ♫

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Pavlov had discovered a fundamental[br]type of learning called "Classical Conditioning."

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An original stimulus elicits an automatic[br]unlearned response.

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Both stimulus and response[br]happen naturally. They are unconditioned.

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Then a second, neutral stimulus, that never[br]elicits the unconditional response by itself,

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is introduced just before the presentation[br]of the original stimulus.

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[bell rings]

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[bell rings]

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[bell rings]

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If the neutral or signaling stimulus is[br]presented alone,

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and a response occurs, as if [br]the original stimulus were still there,

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we say that conditioning has taken place.

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[bell rings]

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The arbitrary neutral stimulus[br]becomes a conditioned stimulus.

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[bell rings]

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The reverse is also true.

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Pavlov and others studied the extinction[br]over time of such conditioned responses.

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[bell rings]

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When the subject learns that the conditioned[br]stimulus no longer signals a desired event,

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[bell rings]

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the acquisition process is reversed[br]as the learned connection is gradually weakened.

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[bell rings continuously]

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Pavlov's work, and the work of those who[br]followed him, led to a remarkable conclusion,

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and that is,[br]any stimulus an organism can perceive

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is capable of eliciting any reaction[br]the organism is capable of making.

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This means that virtually any sound, sight, or smell[br]can influence the way our muscles tense or relax,

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our moods fluctuate, or even the way our[br]attitudes are formed.

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For instance, if I say "Relax," and then do this,

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[gun shot]

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you're going to be startled and upset.

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After five or six pairings of "relax",[br][gun shot]

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just saying the word "relax"

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is going to generate a negative response,[br]rather than its usual learned reaction.