International Journal of Comparative Psychology

Pigeons were studied on a two-component multiple schedule in which key pecking was reinforced on a variable interval (VI) 2-min schedule in both components. In separate phases additional food was delivered on a variable-time (VT) 15-s schedule (response independent) or a VI 15-s schedule (response dependent) in one of the components. In addition to rate, duration of key pecks was measured in an attempt to differentiate the biological and economic effects on key pecking. When components alternated frequently (every 10 s), all pigeons key pecked at a much higher rate during the component with the additional food deliveries, whether response dependent or independent. When components alternated infrequently (every 20 min), pigeons key pecked at high rates at points of transition into the component with the additional food deliveries. Rate of key pecking decreased with time spent in the 20-min component when the additional food was response independent whereas rate of pecking remained elevated when the additional food was response dependent. The additional food deliveries, whether response-independent or response-dependent, however, had no consistent effect on the pigeon's key-peck duration. That is, there were no systematic or reliable shifts in peck duration as would be predicted if short-duration pecks were biologically based. Despite the fact that we were unable to “tag” the biological effect in terms of key-peck duration, the finding that the delivery of response-independent food has different, but predictable effects on responding suggests that animal learning principles can be integrated with species-typical, biological considerations without the need to propose constraints that limit general laws of learning.