Neobehaviorism refers to a brand of behaviorism that utilizes intervening variables, in the form of hypothesized physiological processes, to help explain behavior. Neobehaviorism agreed with older forms of Behaviorism that overt behavior should be Psychology's subject matter but disagreed that theoretical speculation concerning abstract entities must be avoided. Such speculation was accepted provided that the theoretical terms employed are operationally defined and lead to testable predictions about overt behavior.