A review of the behavioral effects of response force: Perspectives on measurement and functions

•This article reviews the literature on the functional roles of response force in learning.•There is broad support for principles of least effort governing the adaptation of behavior to force requirements.•Understanding the motivational effects of force have been hampered by measurement strategies that fail to capture the full range of response variants.•Schedule performance, resistance to extinction, and choice studies have yet to produce a consistent body of findings regarding the functional meaning of force requirements.•The most consistent findings regarding motivational effects indicate force requirements are effective negative reinforcers. Response force is a fundamental dimension of behavior. Yet, little is known about its functional significance for learning. The present review examines the behavioral effects of force across several domains. Along the way, advantages of different measurement strategies that have been used to study force are evaluated. The behavioral functions of force are also considered in light of two commonly expressed notions about behavior. First, the Law of Least Effort predicts that animals and humans will act in ways that minimize the costs of behaving. Second, it is widely held that work requirements and effortful responding are aversive. A review of the literature, especially regarding behavioral adaptations to force, is consistent with the Law of Least Effort on many points. Empirical data are less clear on the aversive properties of force requirements. For much of the literature, there is little in coherent findings. Many disagreements and inconsistencies pertain to measurement strategies that fail to record the full range of response variants. Consistent support for aversive functions of force requirements have been obtained only when studied as a negative reinforcer.