The structure of random ratio responding in humans.

Four experiments explored the rate and structure of human responding on random ratio (RR) schedules of reinforcement, using 3 different methods of analysis. All experiments demonstrated that responding on RR schedules was higher with intermediate ratio values-rates being higher on an RR-30 schedule than on either a RR-10 or RR-60 schedule. All experiments identified 2 distinct types of responding generated by RR schedules: "response-initiation" responding and "within-burst" responding. In contrast to overall rates, response-initiation responding was greatest on RR-10 schedules, and less pronounced as the ratio value increased, but response rates did not vary greatly within the burst (being higher on longer ratio schedules when there was a difference). These findings are consistent with previously obtained data from nonhumans, and suggest human schedule performance should be considered as a joint product of 2 different aspects of responding: response-initiation responding which is sensitive to rates of reinforcement; and within-burst responding which is less sensitive to the molar characteristics of the schedule in operation. The presence of 2 distinct forms of responding may require reinterpretation of many human schedule-controlled phenomena that rely on assumptions about the similarity of all responses to one another.