Psychology Wiki

Assessment | Biopsychology | Comparative | Cognitive | Developmental | Language | Individual differences | Personality | Philosophy | Social |
Methods | Statistics | Clinical | Educational | Industrial | Professional items | World psychology |

Cognitive Psychology: Attention · Decision making · Learning · Judgement · Memory · Motivation · Perception · Reasoning · Thinking  - Cognitive processes Cognition - Outline Index

The law of effect basically states that “responses that produce a satisfying effect in a particular situation become more likely to occur again in that situation, and responses that produce a discomforting effect become less likely to occur again in that situation.”[1]


Early use of the law of effect was applied to neural changes rather than behavioral changes: The strengthening and weakening of neuron connections are due to delightful and unpleasant outcomes respectively. [2]

The law of effect is an operant conditioning. This form of conditioning was first discovered in the 20th century in Cambridge, Massachusetts by Edward L. Thorndike.[3] Edward Thorndike first tested his theory on learning behavior using a customized puzzle box in which a hungry cat was placed. The puzzle box consisted of a lever or a loop that could open the door, thereby releasing the hungry cat to freedom and to the food placed just outside the box. He noted the amount of elapsed time it took the cat to press the lever and free itself. Thorndike discovered that during the first few trials the cat would respond in many ineffective ways, such as scratching at the door, digging at the floor, and pushing at the ceiling, before it discovered the correct solution (pulling the loop or pushing the lever) and was freed from its wooden prison. With each successive trial, it took the cat, on average, less and less time to escape. The cat came to associate the pressing of the lever (or pulling of the loop) with the opening of the door. This has been termed a stimulus – response reaction, with the stimulus "being inside the box" the "pressing of the lever" the response.[4]



Initially, the cat’s responses were largely instinctual, but over time, the pressing lever response was strengthened while the others were weakened

Law of effect can be defined as the primary belief that in learning a pleasing after-effect directly strengthens the connection that produced it.[5]

The law of effect was published by Edward Thorndike in 1905 and states that when an S-R association is established in instrumental conditioning between the instrumental response and the contextual stimuli that are present, the response is reinforced and the S-R association holds the sole responsibility for the occurrence of that behavior. Simply put, this means that once the stimulus and response are associated, the response is likely to occur without the stimulus being present. It holds that responses that produce a satisfying or pleasant state of affairs in a particular situation are more likely to occur again in a similar situation. Conversely, responses that produce a discomforting, annoying or unpleasant effect are less likely to occur again in the situation.

Psychologists have been interested in the factors that are important in behavior change and control since psychology emerged as a discipline. One of the first principles associated with learning and behavior was the Law of Effect, which states that behaviors that lead to satisfying outcomes are likely to be repeated, whereas behaviors that lead to undesired outcomes are less likely to recur.[6]

File:Puzzle box.jpg

Thorndike’s Puzzle-Box. The graph demonstrates the general decreasing trend of the cat’s response times with each successive trial

Thorndike emphasized the importance of the situation in eliciting a response; the cat would not go about making the lever-pressing movement if it was not in the puzzle box but was merely in a place where the response had never been reinforced. The situation involves not just the cat’s location but also the stimuli it is exposed to, for example, the hunger and the desire for freedom. The cat recognizes the inside of the box, the bars, and the lever and remembers what it needs to do to produce the correct response. This shows that learning and the law of effect are context-specific.

In an influential paper, R. J. Herrnstein (1970)[7] proposed a quantitative relationship between response rate (B) and reinforcement rate (Rf):

B = k Rf / (Rf0 + Rf)

where k and Rf0 are constants. Herrnstein proposed that this formula, which he derived from the matching law he had observed in studies of concurrent schedules of reinforcement, should be regarded as a quantification of the law of effect. While the qualitative law of effect may be a tautology, this quantitative version is not.


An example is often portrayed in drug addiction. When a person uses a substance for the first time and receives a positive outcome, they are likely to repeat the behaviour due to the reinforcing consequence. Over time, the person's nervous system will also develop a tolerance to the drug. Thus only by increasing dosage of the drug will provide the same satisfaction, making it dangerous for the user.[8]

Thorndike’s Law of Effect can be compared to Darwin’s theory of natural selection in which successful organisms are more likely to prosper and survive to pass on their genes to the next generation, while the weaker, unsuccessful organisms are gradually replaced and “stamped out”. It can be said that the environment selects the "fittest" behavior for a situation, stamping out any unsuccessful behaviors, in the same way it selects the "fittest" individuals of a species. In an experiment that Thorndike conducted, he placed a hungry cat inside a "puzzle box", where the animal could only escape and reach the food once it could operate the latch of the door. At first the cats would scratch and claw in order to find a way out, then by chance / accident, the cat would activate the latch to open the door. On successive trials, the behaviour of the animal would become more habitual, to a point where the animal would operate without hesitation. The occurrence of the favourable outcome, reaching the food source, only strengthens the response that it produces.

Colwill and Rescorla for example made all rats complete the goal of getting food pellets and liquid sucrose in consistent sessions on identical variable-interval schedules.[9]


The law of effect provided a framework for psychologist B. F. Skinner almost half a century later on the principles of operant conditioning, “a learning process by which the effect, or consequence, of a response influences the future rate of production of that response.”[1] Skinner would later use an updated version of Thorndike’s puzzle box, which has contributed immensely to our perception and understanding of the law of effect in modern society and how it relates to operant conditioning.

See also


  1. 1.0 1.1 Gray, Peter. ‘'Psychology'’, Worth, NY. 6th ed. pp 108–109
  2. A. Charles Catania. "Thorndike's Legency: Learning Selection, and the law of effect", p. 425-426. University of Mary Land Baltimore
  3. Carlson, Neil and et al. "Psychology the Science of Bahaviour", p. 206. Pearson Canada, United States of America. ISBN 978-0-205-64524-4.
  4. Connectionism. Thorndike, Edward.Q Retrieved Dec 10, 2010
  5. Boring, Edwin`. Science. 1. 77. New York: American Association for the Advancement of Science , 2005. 307. Web.
  6. Law of Effect. URL accessed on 2012-08-02.
  7. Herrnstein, R. J. (1970). On the law of effect. Journal of the Experimental Analysis of Behavior, 13, 243-266.
  8. Neil et al., Carlson (2007). Psychology The Science Of Behaviour, New Jersey, USA: Pearson Education Canada, Inc.,.
  9. Nevin, John (1999). "Analyzing Thorndike's Law of Effect: The Question of Stimulus - Response Bonds", Journal of the Experiment Analysis of Behaviour.
This page uses Creative Commons Licensed content from Wikipedia (view authors).