In classical conditioning, behavior that is learned in response to a particular stimulus.
Reflexive behaviors occur when an animal encounters a stimulus that naturally leads to a reflex. For example, a loud noise generates a fright response. If an initially neutral stimulus is paired with the noise, that neutral or conditioned stimulus produces a fright response. In classical conditioning, the response to the conditioned stimulus is called a conditioned response.
Conditioned responses develop in a process called acquisition, in which the natural or unconditioned stimulus is paired with the conditioned stimulus. Some responses develop more quickly than others; similarly, some responses are stronger than others. The nature of the conditioned response depends on the circumstances in which acquisition occurs. The conditioned response emerges most effectively if the conditioned stimulus appears slightly before the unconditioned stimulus. This process is called "delayed conditioning" because the unconditioned stimulus is delayed relative to the conditioned stimulus. The response is weaker if the conditioned and unconditioned stimuli begin together, and becomes even weaker if the unconditioned stimulus precedes the conditioned stimulus. In general, the conditioned response resembles the unconditioned response (e.g., the normal fright response) very closely. Psychologists have shown, however, that the conditioned response is not identical to the unconditioned response and may be very different.
An animal usually produces a conditioned response to stimuli that resemble the conditioned stimulus, a process called stimulus generalization. Balancing this is a complementary tendency not to respond to anything but the conditioned stimulus itself; the process of ignoring stimuli is called stimulus discrimination. The combination of generalization and discrimination leads to appropriate responses.