1) When an organism makes a differential response to two or more stimuli, we can say the animal discriminates between them. This process is called discrimination.

2) The process of responding differently in the presence of different stimuli.

3) Discrimination frequently refers to the control of an operant performance by a discriminative stimulus. Thus, discrimination has occurred when the discriminative stimulus controls the frequency of an operant performance. In this book, we talk about a stimulus controlling a performance rather than the organism discriminating (perceiving) a stimulus or stating that discrimination has occurred.

4) The restriction of responding to certain stimulus situations and not others. Discrimination may be established by differentially reinforcing responding in one stimulus situation and extinguishing or punishing that response in other situations, or by reinforcing other behavior in the other situations.