Pigeons were presented with multiple schedules of alternating 90-sec components. When components in which grain was never presented alternated with components in which grain was presented on a variable-interval schedule, the average rate of responding in the variable-interval components increased, showing overall positive behavioral contrast. Unlike previous reports, this study found that the response rates for all birds increased toward the end of the variable-interval components as training proceeded. This increase in local response rate disappeared when the multiple schedule was composed solely of variable-interval components and reappeared when the variable-interval components were again alternated with extinction. This finding cannot be predicted or explained by recent theories of behavioral contrast based on autoshaping, and thus questions their sufficiency. We suggest that this local response-rate increase results from the predictable change from high to low density of reinforcement at the end of the fixed-duration component. Thus, the present effect apparently illustrates a different type of interaction between components of a multiple schedule than that described by previous theories of contrast. In a given procedure, either or both types of interaction may occur; neither provides a complete account of behavioral contrast.Key words: behavioral contrast, multiple schedules, local response-rate analysis, sequential effects, pigeons When two variable-interval (VI) schedules of grain presentation, which are independent and associated with different stimulus conditions alternate in a multiple schedule, a decrease in the density of reinforcement in one component will usually increase a pigeon's overall rate of key pecking during the unchanged component. This increase in response rate is termed positive behavioral contrast (Reynolds, 1961). Such an increase averaged over the entire component is termed an overall positive contrast effect; an increase in response rate in one portion of the component is termed a local positive contrast effect. Several investigators have shown that overall changes in response rate may be accompanied by particular patterns of local contrast within the component (cf.
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