Final answer:
The conditioned stimulus in the example of Charlie the cat running to the kitchen upon hearing an electric can opener is the sound of the can opener itself, which has been associated with the receipt of food.
Step-by-step explanation:
When Charlie the cat scrambles to his feet and sprints to the kitchen upon hearing the electric can opener, the conditioned stimulus in this example is the sound of the electric can opener itself. Classical conditioning involves learning to associate a neutral stimulus with a stimulus that naturally elicits a response. Here, the can opener's sound, originally neutral, becomes associated with getting food after repeated pairings. As a result, Charlie has learned to anticipate food upon hearing this specific sound, exhibiting a conditioned response which, in this case, is running to the kitchen.
In Pavlov's experiments with dogs, the tone became a conditioned stimulus when paired with the presentation of meat powder, the unconditioned stimulus (UCS), eventually eliciting salivation, the conditioned response (CR). Similarly, Charlie's reaction to the sound of the can opener is an example of a conditioned response to the conditioned stimulus.