Book Definition: In classical conditioning, the stimulus that elicits an unconditioned response.

In Your Own Words

  • Stimulus which produces a response from the subject naturally, or without conditioning.
  • Stimulus that produces a natural response or reflex.
  • Stimulus that causes a natural reaction.
  • Stimulus that causes an uncontrolled natural reaction.
  • Specifically the stimulus. Unconditioned stimulus and unconditioned response are not the same thing. Unconditioned stimulus causes the unconditioned response.
  • The natural reaction as inspired by the situation not by conditioning.


  • Unconditioned Stimulus
  • The food used in Pavlov's dog experiment. Made the dogs salivate (something that is natural and uncontrolled)
  • The unconditioned stimulus: the smell of onions and sweaty gym socks ; the reflexive response it produces: the gases being released cause your eyes to water. (You cannot control this reaction)
  • Blinking when someone fakes a punch in front of your face. The punch is the UCS, and blinking is the UCR.
  • Closing your eyes if there is a bright light in front of them. The bright light is the UCS, and blinking is the UCR.
  • Getting a whiff of pepper (UCS) and then sneezing (UCR).
  • Getting a shot (UCS) then you feel pain (UCR). Pain is not a voluntary response.
  • The smell of coffee (UCS) to a tired student produces salivation (UCR).
  • The loud noise (UCS) in the Little Albert experiment created fear (UCR)

Additional Resources