General Chemistry
Behavioral Sciences
Lab Techniques

Classical Conditioning: Stimulus and Response

In classical conditioning, we deal with stimuli and responses. A stimulus is something in the environment that elicits a reaction, like the smell of food making you hungry. A response is the behavior that follows a stimulus, such as salivating when you smell that food.

Unconditioned vs. Conditioned

Unconditioned (UC) means it’s natural; no learning needed. An unconditioned stimulus (UCS) naturally triggers an unconditioned response (UCR) without any prior training. For instance, when you smell your favorite food (UCS), you start to drool (UCR). It’s a built-in reaction.

On the flip side, conditioned stuff (C) involves learning. A conditioned stimulus (CS) is neutral until it’s associated repeatedly with the UCS. After enough pairings, the CS alone can trigger a conditioned response (CR), which is the same as the UCR, but now that same behavior is being triggered by the new learned stimulus (UCS).

Which One Is It?: A Quick Guide

MCAT questions will often ask you to determine whether something is a UCS, UCR, CS, or CR. The scenarios can make picking this out a little tricky so let’s go over how to spot the different variables by breaking this down in to two steps: 1) determining whether something is a stimulus or response and then 2) by figuring out whether it is unconditioned or conditioned. To do this we will look for the following:

  1. Is it a stimulus or a response?
    • Stimulus: It triggers a behavior (like the smell of food).
    • Response: It’s the behavior itself (like salivating).
  2. Is it UC or C?
    • Unconditioned: It happens naturally (smelling food makes you hungry without you having to learn to feel that way).
    • Conditioned: It’s learned (you hear a bell every time before you get to eat, and eventually, the bell alone makes you hungry).

Now let’s take a look at an example and how this approach can help us identify the different variables. To do this we will be looking at the flinching in response to a loud noise.

Unconditioned Stimulus (UCS): A sudden, loud bang such as a firecracker exploding. This naturally makes you flinch.

Unconditioned Response (UCR): The flinch or startle itself. You didn’t need to learn to do this; it’s an automatic reflex.

Now, let’s add classical conditioning to this scenario.

Imagine every time before the loud bang, a red light flashes. Initially, the red light on its own means nothing – it’s a neutral stimulus. However, if the red light flashes before the bang happens consistently, over time, you learn to associate the two.

Conditioned Stimulus (CS): The red light, which was neutral, but after association with the bang, it now triggers a reaction.

Conditioned Response (CR): The flinch or startle response when you see the red light, even without the loud bang following.

Breakdown of the Example:

  1. Response or Stimulus? – You’re looking for what triggers the action (stimulus) and the action itself (response).
    • The loud bang and the red light are stimuli. (These are the triggers)
    • The flinch is the response. (This is a behavior)
  2. UC or C? – Is the action learned or automatic?
    • The automatic jump from the loud bang is the unconditioned response. (Loud noises make us jump automatically no prior learning needed)
    • The learned jump from the red light is the conditioned response. (Red lights don’t automatically make you flinch so this is going to take learning)

By following these steps, you can identify and differentiate between the unconditioned and conditioned elements of this classical conditioning example.

Term Summary

  • Stimulus: An environmental event that elicits a reaction.
  • Response: A behavior that follows a stimulus.
  • Unconditioned Stimulus (UCS): A stimulus that naturally triggers a response without the need for learning.
  • Unconditioned Response (UCR): A natural, automatic reaction to an unconditioned stimulus.
  • Conditioned Stimulus (CS): A previously neutral stimulus that, after being associated with an unconditioned stimulus, triggers a conditioned response.
  • Conditioned Response (CR): A learned behavior that results from the conditioned stimulus.