Experimental psychology approaches psychology as one of the natural sciences, and therefore assumes that it is susceptible to the experimental method. Many experimental psychologists have gone further, and have assumed that all methods of investigation other than experimentation are suspect. In particular, experimental psychologists have been inclined to discount the case study and interview methods as they have been used in clinical and developmental psychology.

Since it is a methodological rather than a substantive category, experimental psychology embraces a disparate collection of areas of study. It is usually taken to include the study of perception, cognitive psychology, comparative psychology, the experimental analysis of behavior, and some aspects of physiological psychology and developmental psychology.