Ivan Pavlov studied the reflexive flow of saliva in dogs. He used meat powder or other food to trigger the salivation. It was later observed that the salivation in the dog was triggered even before the food was placed in its mouth. In this experiment, was the unconditioned response.

Conditioned stimulus

Explanation:

The conditioned stimulus is the neutral stimulus of classical conditioning before conditioning. It becomes associated with the unconditional stimulus, which will eventually trigger the conditional response. Ivan Pavlov has been proposed classical conditioning. In classical conditioning there are  

Thus in the above experiment, The conditional stimulus was the unconditional response.  

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