CHANGEOVER RATIO EFFECTS ON CONCURRENT VARIABLE‐INTERVAL PERFORMANCE¹

Abstract

Rats' bar-pressing was maintained by concurrent variable-interval schedules of reinforcement. A fixed-ratio of pulls on a chain (the changeover ratio) was required for switching between schedules. The first experiment employed equal variable-interval schedules and symmetrical changeover ratios. Increasing these ratios resulted in a decrease in the rate of switching between schedules and an increase in local response rate. In the second experiment, a range of asymmetrical changeover ratios was used with equal variableinterval schedules, and a preference wvas found for the schedule associated with the larger switching-into ratio. Both the distributions of responses and time between the two schedules deviated from those expected on the basis of obtained reinforcers. In the third experiment, the switching-out-of ratio was dependent on the amount of time spent in a variable-interval 2-minute schedule; a constant ratio permitted switching out of the alternative variable-interval 1-minute schedule. A strong preference was shown for the variable-interval 2-minute schedule. The fourth experiment used equal variable-interval schedules; one changeover ratio was varied while the second remained constant. The results failed to show systematic differences in local response rates immediately after a changeover.Key words: changeover ratio, concurrent schedules, matching, variable-interval, chainpull, lever press, rats Two methods have been used for programming schedules associated with concurrent operants: one involves a separate manipulandum for each of the operants, with the restriction that responding simultaneously on two or more manipulanda is not possible; the other provides a distinct manipulandum for switching between schedules, with two or more operants performed on another manipulandum, each associated with different stimulus conditions. Results from these two methods appear to be equivalent over a wide range of experimental manipulations (Catania, 1966

The effects of changeover delays of fixed or variable duration on concurrent variable-interval performance in pigeons

“…Similar results were reported by Bourland and Miller (1978) and Killeen (1972). On the other hand, Guilkey, Shull, and Brownstein (1975) and White (1979) failed to observe this rate difference when they used a FR changeover requirement. Pliskoff, Cicerone, and Nelson (1978) …”

“…Second, it was consistently found that the differences between COD and post-COD response rates were greatly reduced when a COD of variable, rather than fixed, duration was used. Other researchers (Guilkey et al, 1975;Pliskoff et al, 1978;White, 1979) have also failed to obtain a substantial increase in response rates immediately after the CO response when they used a FR changeover requirement instead of a COD of fixed duration. The results of their experiments together with the present findings indicate that elevated response rates immediately after the CO response may occur only when a COD of fixed duration is used.…”

“…Increases in the duration of the COD result in a decrease in the number of CO responses (Allison & Lloyd, 1971;Brownstein & Pliskoff, 1968;Shull & Pliskoff, 1967). An increase in shock intensity or in the duration of a time-out period following a CO response has similar effects (Todorov, 1971), as does an increase in a fixed-ratio (FR) requirement scheduled on the CO key (Stubbs & Pliskoff, 1969;White, 1979). The number of CO responses varies also as a function of the difference in reinforcement frequency between the two components of the schedule.…”

Suboptimal choice in nonhuman animals: Rats commit the sunk cost error

“…It is known that increasing the ratio required to switch schedules, under concurrent scheduling in one key, will increase the time a pigeon spends in one schedule before it makes a switch response (Findley, 1958). More specifically, White (1979) has shown that switching between concurrent variableinterval schedules in rats becomes less likely when the FR requirement for the switching response is increased. That is, increasing the cost of switching increases persistence in one schedule before a switch response is performed.…”

Local Rates of Responding and Reinforcement During Concurrent Schedules

“…Second, no study reported a significant difference between the local rates of reinforcement when the components differed in only minor ways, such as the discriminative stimuli used to signal the components or the position of the operanda that produced reinforcers (Marcucella & Margolius, 1978;McSweeney & DeRicco, 1976;White, 1979, Experiment 1).…”