Narrator: Behavioral psychologists have
come up with new views,

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

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

Because we are all truly born to learn.

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

wasn't concerned with the subject at all.

At least, not at first.

Pavlov, a noted Russian scientist,

won the Nobel Prize for Physiology
and Medicine in 1904.

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

and the action of the salivary glands.

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

if and how much they salivated
during digestion.

When food was presented,
the dog salivated quickly,

an inherited salivary reflex.

But over repeated testings,
a strange thing happened.

The dog salivated
before contact with the food.

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

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

was enough to trigger this built-in reflex.

What was going on to elicit this response?

Pavlov decided to find out,
by systematically varying the stimuli

and measuring the dogs' reaction.

[Metronome clicking]

Metronomes, lights, and bells
were all used as stimuli,

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

What mattered was not the kind of
stimulus that was used,

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

♫ Electronic Music ♫

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

An original stimulus elicits an automatic
unlearned response.

Both stimulus and response
happen naturally. They are unconditioned.

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

is introduced just before the presentation
of the original stimulus.

[bell rings]

[bell rings]

[bell rings]

If the neutral or signaling stimulus is
presented alone,

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

we say that conditioning has taken place.

[bell rings]

The arbitrary neutral stimulus
becomes a conditioned stimulus.

[bell rings]

The reverse is also true.

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

[bell rings]

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

[bell rings]

the acquisition process is reversed
as the learned connection is gradually weakened.

[bell rings continuously]

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

and that is,
any stimulus an organism can perceive

is capable of eliciting any reaction
the organism is capable of making.

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

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

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

[gun shot]

you're going to be startled and upset.

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

just saying the word "relax"

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