Patterning with fixed-time schedules of response-independent reinforcement.

Pigeons were first exposed to a schedule providing food when the time between successive key pecks (the interresponse time) exceeded a specified duration. When food then was presented at regular intervals independent of responding (fixed-time schedule), responses typically occurred at a steady rate in the periods between successive food presentations. Once the birds had been exposed to a fixed-ratio schedule, however, response rate under fixed-time schedules was positively accelerated. Variations in the sequence of conditions given different subjects indicated that the changes in patterning were due to the fixed-ratio schedule, rather than to the number of transitions from a response-dependent to the response-independent fixed-time schedule, to changed parameter values, or to prolonged experience with the fixed-time schedule. The effects of fixed-time schedules on patterning depended upon experimental history.