Some factors involved in the stimulus control of operant behavior.
The stimuli which are present when an operant is reinforced modify the subsequent frequency of emission of the response. For example, if a hungry pigeon is reinforced with food when it pecks a translucent key upon which a monochromatic light is projected, it will subsequently peck most rapidly when the light is of the same wavelength. Guttman (3) has reported that a difference of 2 millimicrons can produce a lower rate. As the difference increases the rate falls in a "generalization gradient." If responses are reinforced at one wavelength and extinguished at all others, the gradient is sharpened. These facts are now well known, but the significance of the relevant conditions has not been fully analyzed.