Effects of drugs on stimulus control of behavior. II. Degree of stimulus control as a determinant of effect

Pigeons were trained to peck one of two concurrently available, differently colored response keys (red or amber) depending on the presence or absence of a houselight that provided general illumination of the experimental chamber. When the houselight was illuminated, only responses on a red key were reinforced (red-key responses designated SD responses; amber-key re-sponses designated Sa responses); when the houselight was not illuminated, only responses on an amber key were rein-forced (amber-key responses designated 5D responses; red-key responses designated Sa responses). Under one proce-dure, every 5D response was reinforced (fixed-ratio 1 sched-ule), whereas under a second procedure, the first SD response after the elapse of a 5-mm interval was reinforced (fixed-interval 5-mm schedule). Both the rates of responding and the stimulus control over responding exerted by the houselight were as