Applied behavior analysis
A discriminative stimulus (SD) is something that tells a person that reinforcement is available. The presentation of a SD should cause a response. Differential reinforcement teaches a person the difference between a SD and a non-discriminative stimulus (S-delta). A SD signals that reinforcement is available. A S-delta does not tell the person anything about the availability of reinforcement. A S-delta is not likely to produce responses because there is reinforcement is not given.