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Classical conditioning: Neutral, conditioned, and unconditioned stimuli and responses
Video transcript
So I have a pet guinea pig. And here she is. And one thing that guinea
pigs love, like all pets do, is when they get a treat. Now, my guinea pig
happens to love carrots. And whenever I give her a
carrot, she acts very excited. It's actually really cute
to see her so excited. And it makes me kind
of jealous because I wish I could get so excited
about a raw vegetable because imagine how much
healthier I would be. But for her, that
excitement comes naturally. I never had to train
her to enjoy carrots. When she was first
living in my apartment, I used to like to surprise
her by getting a carrot out of the refrigerator and
bringing it over to her cage. Now the thing you need to
know about my refrigerator is that the door
is always stuck. So I have to pull pretty
hard to get it open. And when I do, that makes
a loud popping sound. So after a few weeks
of my guinea pig living in my
apartment, I discovered that I couldn't
surprise her any more with a carrot because
as soon as she heard the sound of the refrigerator
door being pried open, she was already acting
excited, even before I gave her a carrot. I also noticed that when I
would open the refrigerator to make a snack
for myself, she'd respond to the sound of
the door by acting excited, even if she wasn't
going to get a carrot. This learned response
that she developed to the sound of a
refrigerator door is referred to in psychology
as classical conditioning. Whether you realize it or
not, classical conditioning is a topic that you're
already very familiar with. The concept of
classical conditioning is easy to understand. The challenge is
understanding and applying the correct terminology. So let's talk about
that terminology. So I'm going to
write S for stimulus. And a stimulus is anything
that stimulates your senses. It's anything you can hear,
see, smell, taste, or touch. And stimuli can produce
a response, which I'll write as an R. So a
stimulus produces a response. So let's use this example
to make the terms clear. No one had to
teach my guinea pig to act excited about carrots. It's her normal,
physiologic response. And since no one had to
teach her that about carrots, we can refer to the carrot
as an unconditioned stimulus, which I'll write as UCS. An unconditioned
stimulus triggers some kind of
physiologic response. So in our case, the carrot
triggers excitement. The excitement is the response. And in fact, the
more descriptive way to refer to this
response is to call it an unconditioned response. So an unconditioned
stimulus elicits an unconditioned response. So you might be asking
yourself why complicate things by sticking the term
unconditioned in front of it? Well, as we're
about to see, there are different types of
stimuli and responses. So for now, think of
the word unconditioned as something you
already do naturally. And if something
happens naturally, then it really wasn't learned. It's an innate process. Conditioned, on the other hand,
means something is learned. And remember,
classical conditioning is a type of learning. So you can remember
conditioning means to learn. If you've ever heard someone
use the phrase, I'm conditioning myself to like it,
said differently, I'm learning to like it. So unconditioned means
it happens naturally. Conditioned means
it was learned. Now, think of what
was happening right before she got her carrot. My refrigerator
door opened, which made a loud popping sound. So we can refer to the sound of
the door as a neutral stimulus. A neutral stimulus
is something that you can sense by either
seeing it, tasting it, or in our case hearing it. But it doesn't produce
the reflex being tested. So in our case, the
refrigerator door can be heard. But the sound of the
door doesn't naturally cause excitement. That's something that
had to be learned, which is why she didn't
respond the first few times she heard it. So since the refrigerator
door doesn't cause excitement on its own, we say
the refrigerator door is a neutral stimulus
that is immediately followed by the unconditioned
stimulus of the carrot, which causes the unconditioned
response of excitement. Now, classical
conditioning is established when the neutral stimulus
is presented, followed a short time later by the
unconditioned stimulus, and the presentation of both
stimuli is called a trial. So pairing these
two stimuli together is how you establish
classical conditioning. But see, in my
case I didn't know I was establishing
classical conditioning. But I really was. I was pairing the sound of the
refrigerator door being opened with the presentation
of a carrot. And classical
conditioning actually occurs when the neutral
stimulus, in our case the sound of the
refrigerator door, is able to elicit
the same response as the unconditioned
stimulus, the carrot. So in our example, we can say
classical conditioning had taken place when the sound
of the refrigerator door alone was enough to
cause excitement, even if she didn't
receive the carrot. And when this has
happened, we say the neutral stimulus
is no longer neutral. And now it's the
conditioned stimulus, because its acquired the ability
to elicit a response that was previously elicited by
the unconditioned stimulus, the carrot. So there's that word again,
conditioned and conditioned stimulus, which as I said
earlier means learned. My guinea pig was
conditioned to respond to the sound of the refrigerator
by behaving excited. And the excited
response that's now associated with the
refrigerator door is no longer the
unconditioned response because in this context
she had to learn to respond with excitement
to the sound of the door. So the proper term
for this response is called a conditioned
response because it is a learned response. So that's the idea behind
classical conditioning. And because of it, I now
feel obligated to have to give my guinea
pig a carrot any time I open the refrigerator.