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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.