These sorts of control are brought about by a variety of methods and they can explain many aspects of behavioral processes.
After a discriminative stimulus is established, similar stimuli are found to evoke the controlled response.
The results showed a generalization gradient: the more the wavelength differed from the trained stimulus, the fewer responses were produced.
One is illustrated by the remainder of Hanson's study, which examined the effects of discrimination training on the shape of the generalization gradient.
An earlier theory involving inhibitory and excitatory gradients partially explained the results,[8] A more detailed quantitative model of the effect was proposed by Blough (1975).
[9] Other theories have been proposed, including the idea that the peak shift is an example of relational control; that is, the discrimination was perceived as a choice between the "greener" of two stimuli, and when a still greener stimulus was offered the pigeons responded even more rapidly to that than to the originally reinforced stimulus.
Of particular note is the "delayed matching to sample" variation, which has often been used to study short-term memory in animals.
[12] Psychoactive cannabinoids produce discriminative stimulus effects by stimulation of CB1 receptors in the brain.