Key pecking of 4 pigeons was studied under a two-component multiple schedule in which food deliveries were arranged according to a fixed and a variable interfood interval. The percentage of response-dependent food in each component was varied, first in ascending (0, 10, 30, 70 and 100%) and then in descending orders, in successive conditions. The change in response rates was positively related to the percentage of response-dependent food in each schedule component. Across conditions, positively accelerated and linear patterns of responding occurred consistently in the fixed and variable components, respectively. These results suggest that the response-food dependency determines response rates in periodic and aperiodic schedules, and that the temporal distribution of food determines response patterns independently of the response-food dependency. Running rates, but not postfood pauses, also were positively related to the percentage of dependent food in each condition, in both fixed and variable components. Thus, the relation between overall response rate and the percentage of dependent food was mediated by responding that occurred after postfood pausing. The findings together extend previous studies wherein the dependency was either always present or absent, and increase the generality of the effects of variations in the response-food dependency from aperiodic to periodic schedules.
The occurrence of extinction bursts—transient increases in response rate in excess of those observed in baseline during the period immediately following discontinuation of reinforcement of a response—was examined. In Experiment 1, key pecking of pigeons was reinforced according to a multiple schedule in which a variable‐ratio schedule alternated with an interval schedule in which the reinforcers were yoked to the preceding variable‐ratio component. In Experiments 2 and 3, rats were screened such that the lever‐press response rates of different rats maintained by variable‐interval schedules were either relatively high or relatively low. Following these baseline conditions, in Experiments 1 and 2 responding was extinguished by eliminating the food reinforcer and in Experiment 3 by removing the response–reinforcer dependency. Responses immediately following extinction implementation were examined. Response increases relative to baseline during the first 20 min of a 324.75‐min extinction session (Experiment 1) or during the first 30‐min extinction session (Experiments 2 and 3) were rare and unsystematic. The results (a) reinforce earlier meta‐analyses concluding that extinction bursts may be a less ubiquitous early effect of extinction than has been suggested and (b) invite further experimentation to establish their generality as a function of preceding reinforcement conditions.
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