Taking purpose into account in experimental psychology: testing for controlled variables.

Experimental research in psychology is based on a causal model--the General Linear Model (GLM)--that assumes behavior has causes but not purposes. Powers (1978) used a control theory analysis to show that the results of psychological experiments based on such a model can be misleading if the organisms being studied are purposeful (control) systems. In the same paper, Powers presented evidence that organisms are such systems. Nevertheless, psychologists continue to use methods that ignore purpose because the behavior in most experiments appears to be non-purposeful (a caused result of variations in the independent variable). The experiments described in this paper show how purposeful behavior can appear to be caused by the independent variable when an organism's purposes are ignored. The results show how taking purpose into account using the control theory-based "Test for the Controlled Variable" can provide a productive new methodological direction for experimental research in psychology.