Lever Pressing in Expanding or Collapsing Intervals of Nonresponse-Contingent Reward: Sensitivity to Pretraining
16 rats that had been given either one or two training days of 50, response-contingent rewards per day were placed upon one of two schedules in which the daily interval between nonresponse-contingent rewards was either increased or decreased. In the expanding time condition, the fixed interval of nonresponse-contingent reward delivery changed from 10 sec. to 14 min. over 9 consecutive days while in the collapsing-time condition, the intervals were reduced from 14 min. to 10 sec. over the same duration. Whereas both one-day and two-day training groups in the collapsing-time condition and the two-day group in the expanding-time condition demonstrated typical extinction profiles, the one-day expanding-time group maintained significantly higher total responses over the entire period.