Visual effects of opiates in pigeons. III. Luminance and wavelength sensitivity.

In a psychophysical task that permitted dissociations among sensitivity, overall stimulus control, and bias, pigeons learned to discriminate among stimuli along separate wavelength and luminance dimensions. Subsequent tests followed injections of morphine (1-8 mg/kg) and morphine plus naloxone (3 mg/kg). Morphine decreased sensitivity to both dimensions, and reduced overall control by luminance. These effects were reduced or reversed by naloxone. Morphine's effects appeared more pronounced for luminance than for wavelength stimuli. There were no consistent drug effects on response bias.