DISCRIMINATIVE STIMULUS EFFECTS OF COMBINATIONS OF DRUG AND VISUAL-STIMULI IN PIGEONS

Six pigeons were studied to determine whether the brightness of a hous elight interacted with the stimuli produced by methadone, and whether the nature of the interaction depended on the order of training of the two discriminations. Three pigeons were trained to peck the right key after methadone (2.0 mg/kg) and the left key after saline, when the h ouselight was dim. The effects of a range of methadone doses (0.5, 1.0 , 2.0 mg/kg and saline) were tested. Three other pigeons were trained, in the absence of drug, to peck the right key when the houselight was dim and the left key when the houselight was bright. The effects of a range of houselight intensities were tested. Then, for both groups, r ight-key pecks were reinforced in the presence of methadone and the di m houselight, and left-key pecks were reinforced in the presence of sa line and the bright houselight. Methadone doses were tested in the pre sence of both houselight brightnesses used in training. All pigeons pe cked the methadone-appropriate key after high doses of methadone, rega rdless of houselight intensity. All pigeons trained to discriminate ho uselight brightness first, and one of the pigeons trained to discrimin ate methadone first, pecked according to the houselight condition when saline and lower doses were tested. In the other pigeon trained to di scriminate methadone first, pecking was more related to drug dose. The se data show that a drug stimulus can compete with external stimuli fo r behavioral control, that a drug stimulus can assume control over beh avior originally controlled by external stimuli, and that discriminati ons based on external stimuli may be retained when saline or low doses of drug are administered.