The sudden reappearance of a previously extinguished behavior is called spontaneous recovery, and the conditions under which this recovery is possible depend strongly on the duration of the initial pairing, the length of extinction, and the overall intelligence of the organism (more intelligent organisms can "hold onto" extinguished behaviors for longer before forgetting them entirely).

Coined by Skinner, the term respondent behavior is more generally used to describe any end-result changed behavior in an organism after sufficient exposure to classical conditioning techniques.

An unconditioned response is a response to a stimulus that takes place automatically as a result of biological or physical processes, without being under the conscious control of the organism. Pairing an unconditioned response with a neutral stimulus can lead to the formation of conditioned responses through association.

Acquisition also refers to the point in operant conditioning where a reinforced response is strengthened via reinforcement, schedule adjustment, or punishment.

More generally, discrimination occurs when an organism learns to distinguish between those stimuli which provoke the conditioned response and stimuli which do not provoke an unconditioned response.

This is an example of classical conditioning because learning (e.g. changes in fetal activity) occurred when music was played, as a result of several weeks of pairing relaxation exercises with music. This indicates that music was the conditioned stimulus (CS), and the exercises were the unconditioned stimulus (US). With operant learning, there are contingencies between specific behaviors and rewards (e.g. a rat receiving a pellet when pressing a lever). Because there is no contingency or reward here, it cannot be defined as operant learning.

A “generalized reinforcer” is the correct answer, because a generalized reinforcer obtains reinforcing functionality through its association with other reinforcers (i.e. money can be used to purchase things that may act as reinforcers themselves).

The first phase of classical conditioning is called acquisition. This is when the organism begins to learn that the pairing of the two stimuli is not random, and they can expect them to occur together. The organism is acquiring the new learning during this phase.

"Classical conditioning" is a type of learning in which a stimulus acquires the capacity to evoke a response that was originally evoked by another stimulus. In this case, fear was originally evoked by a specific dog. Now, Peter feels fear even when looking at pictures of other dogs that are non-threatening. The other choices are incorrect. "Operant conditioning" is learning that occurs through reinforcement (e.g. rewards, punishment), "modeling" is learning that occurs through observation, and "spontaneous recovery" is when a previously extinguished response reappears.