Five pigeons were trained on a variety of concurrent interval schedules that arranged reinforcements at either fixed or variable times after the last reinforcement. Two measures were obtained: the number of responses on each schedule, and the time spent responding on each schedule. Ratios of response rates on the two schedules did not equal ratios of reinforcement rates when both schedules were variable nor when one was variable and the other fixed. Ratios of times spent responding approximately equalled ratios of reinforcement rates when both schedules were variable, but did not do so when one was fixed. (Nevin, 1971;Trevett et al., 1972). It differed from these experiments in that the concurrent schedules were arranged according to the switching procedure (Findley, 1958), rather than the two-key procedure. METHOD SubjectsFive homing pigeons, numbered 21, 23, 24, 25, and 26, were maintained at 80% + 15 g of their free-feeding weights. The birds had previously been trained on conc Fl Fl schedules (White and Davison, 1973). ApparatusThe experimental chamber, situated remote from conventional relay control equipment, was sound-attenuated and external noise was masked by an exhaust fan. A food hopper was situated 10 cm from the grid floor, midway between two translucent response keys 2 cm in 191 1975, 24,[191][192][193][194][195][196][197] NUMBER 2 (SEPTEMBER)

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Six pigeons were trained on multiple variable-interval schedules and performance was measured in the presence or absence of another variable-interval schedule (the common schedule) arranged concurrently with both components. Manipulations included varying the rate of reinforcement on the common schedule, leaving the common schedule unchanged while the components of the multiple schedule were varied, varying the multiple schedule components in the absence of the common schedule, and varying one component of the multiple schedule while the other component and the common schedule were unchanged. The normal rate-increasing and rate-decreasing effects of reinforcement rate increase were found, except that changing one multiple schedule component did not affect the response rate in the successively available common schedule component. (Baum, 1974) and is typically close to 1.0 for both multiple and concurrent schedules. The parameter a describes the sensitivity of the response-rate ratio to changes in the ratio of reinforcement rates (Lander and Irwin, 1968). The value of a typically obtained across a variety of procedural variations for concurrent variable-interval (VI) schedules is between 0.7 and 1.0

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