Stimulus Discrimination occurs when an organism learns to respond differently to two or more stimuli based on whether reinforcement is available. In this process, a discriminative stimulus (SD) signals the availability of reinforcement, while the absence of the SD, or the presence of an S-delta (S∆), signals that reinforcement is not available.
Example
A student raises their hand in class (SD) because they know the teacher will call on them and provide attention (reinforcement). However, when the teacher is not in the room (S-delta), raising their hand will not result in attention, so the behavior of hand-raising decreases in that situation. This shows stimulus discrimination between when the teacher is present versus absent.