Classical (Pavlovian) and instrumental (Thorndikian) conditioning are the two most widely employed paradigms for studying simple, associative learning resulting from the organism's exposure to the temporal conjunction of two or more events. The fully specified classical conditioning paradigm consists of a set of operations involving an unconditioned stimulus (US) reliably producing an unconditioned response (UR) and a conditioned stimulus (CS) initially shown not to produce a response resembling the UR. The CS and US are then presented repeatedly to the organism in a specified order and temporal spacing, and a response similar to the UR develops to the CS that is called the conditioned response (CR); that is, CS-CR functions are obtained. Control over the temporal conjunction of the CS, US, and UR makes classical conditioning preparations ideal vehicles for studying associative learning because they can uniquely specify stimulus antecedents to the...