Editing Law of effect (section)

== Definition ==
[[File:Lawofeffect.gif|thumb|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 is the belief that a pleasing after-effect strengthens the action that produced it.<ref>Boring, Edwin`. Science. 1. 77. New York: American Association for the Advancement of Science, 2005. 307. Web.</ref>

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 [[Stimulus (psychology)|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.<ref>{{cite web|url=http://www.enotes.com/gale-psychology-encyclopedia/law-effect |title=Law of Effect |publisher=eNotes.com |date= |accessdate=2012-08-02}}</ref>

[[File:Puzzle box.jpg|thumb|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, [[Richard Herrnstein|R. J. Herrnstein]] (1970)<ref>Herrnstein, R. J. (1970). On the law of effect. ''Journal of the Experimental Analysis of Behavior, 13'', 243-266.</ref> proposed a quantitative relationship between response rate (''B'') and reinforcement rate (''Rf''):
<div class="center">
''B'' = ''k'' ''Rf'' / (''Rf''<sub>0</sub> + ''Rf'')
</div>
where ''k'' and ''Rf''<sub>0</sub> 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.

=== Example ===
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 behavior 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.<ref>{{cite book|last=Neil|first=Carlson|title=Psychology The Science Of Behaviour|year=2007|publisher=Pearson Education Canada, Inc.|location=New Jersey, USA|page=516|display-authors=etal}}</ref>

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.<ref>{{cite book| last=Nevin |first=John|title="Analyzing Thorndike's Law of Effect: The Question of Stimulus - Response Bonds"|year=1999|publisher=Journal of the Experiment Analysis of Behaviour|page=448}}</ref>