Human choice on concurrent variable-interval variable-ratio schedules

Each of 5 adult male humans sat in a 4 degrees C room where they could warm themselves by illuminating six heat lamps for 10-second periods according to a concurrent variable-interval variable-ratio schedule. Left-button presses on a response panel switched between the schedules and started a 2-second changeover delay. Right-button presses illuminated the heat lamps if assigned by the associated schedule and if the changeover delay had timed out. Panel lights identified the schedule in effect and each effective right-button press. A discrimination procedure--either a multiple variable-interval variable-ratio schedule or the presentation of each schedule individually on alternate days--preceded exposure to the choice procedure for some subjects. For subjects not exposed to a discrimination procedure prior to exposure to choice, or if such exposure failed to result in higher rates to the ratio than to the interval schedule, relative response rates matched relative reinforcement rates. However, if subjects responded at higher rates to the ratio schedule than to the interval schedule during a prior discrimination procedure, relative rates on a subsequent choice procedure deviated from matching in the direction of reinforcement-rate maximizing. In eight of 11 conditions, choice appeared to be governed by maximizing processes. In all cases, human concurrent ratio-interval performances differed from those of nonhumans in that matching was never obtained with local ratio-interval rate differences.