Elicitation of a response by a stimulus that normally does not elicit that response. The response is one that is mediated primarily by the autonomic nervous system (ans) (such as salivation or a change in heart rate). A previously neutral stimulus is repeatedly presented just before an unconditioned stimulus that normally elicits that response. When the response subsequently occurs in the presence of the previously neutral stimulus, it is called a conditioned response, and the previously neutral stimulus is called a conditioned stimulus.