Stimulus control
In behavioral psychology, stimulus control is a phenomenon that occurs when an organism behaves in one way in the presence of a given stimulus and another way in its absence. Thus, stimulus control of behavior occurs when the performance of a behavior is controlled by the presence or absence of an antecedent discriminative stimulus. For example, the presence of a stop sign, a discriminative stimulus, increases the probability that "braking" behavior will occur.
Some theorists believe that all behavior is under some form of stimulus control. For example, in the analysis of B. F. Skinner,verbal behavior is a complicated assortment of behaviors with a variety of controlling stimuli.
The controlling effects of stimuli are seen in quite diverse situations and in many aspects of behavior. For example, a stimulus presented at one time may control responses emitted immediately or at a later time; two stimuli may control the same behavior; a single stimulus may trigger behavior A at one time and behavior B at another; a stimulus may control behavior only in the presence of another stimulus, and so on. These sorts of control are brought about by a variety of methods and they play a large role in systematic accounts of behavioral processes.
In simple, practical situations, for example if one were training a dog using operant conditioning, optimal stimulus control might be described as follows:
Operant stimulus control is typically established by discrimination training. For example, to make a light control a pigeon's pecks on a button, reinforcement only occurs following a peck to the button. Over a series of trials the pecking response becomes more probable in the presence of the light and less probable in its absence, and the light is said to become an SD. Virtually any stimulus that the animal can perceive may become a discriminative stimulus, and many different schedules of reinforcement may be used to establish stimulus control. For example, a green light might be associated with a VR 10 schedule and a red light associated with a FI 20-sec schedule, in which case the green light will control a higher rate of response than the red light.
Procedures for generating generalization gradients in operant conditioning are similar to those for used in classical conditioning, as described above. An important early example is an experiment by Hanson (1959). First a group of pigeons was reinforced for pecking a disc illuminated by a light of 550 nm wavelength, and never reinforced otherwise. Reinforcement was then stopped, and a series of different wavelength lights was presented one at a time. The results were plotted as a generalization gradient, as in the tone generalization experiment described above. The more the wavelength differed from the trained stimulus, the fewer responses were produced.
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