Operant-Pavlovian interactions: Ratio-schedules and the effects of the duration and location of a stimulus preceding response-independent food.

Two groups of four pigeons were exposed to either a fixed-ratio or a random-ratio schedule of reinforcement. Presentation of stimuli which preceded response-independent food delivery was then superimposed upon this operant baseline. The duration and the location of stimulus presentation were varied in different experimental conditions. Random-ratio schedules maintained higher response rates than fixed-ratio schedules. Response rates during presentation of the stimulus on the operant key exceeded response rates in the absence of stimulus presentation for the fixed-ratio subjects, but not for the random-ratio subjects. Similar observations were made when stimulus presentation occurred on a seperate stimulus key. During stimulus presentation on the stimulus key, response rates on the operant key were considerably higher for the random-ratio subjects than for the fixed-ratio subjects, especially during longer presentation of the stimulus (30 sec).