Goldberg S R, Kelleher R T, Goldberg D M
J Pharmacol Exp Ther. 1981 Jul;218(1):271-81.
Squirrel monkeys pressed a key under second-order schedules in which every nth response resulted in a 2-sec visual stimulus (n-response fixed ratio; n = 10, 20 or 30); after a minimum fixed-interval of time elapsed (second-order t-min fixed-interval; t = 5 or 60), the completion of a fixed-ratio resulted in both the brief stimulus and either presentation of food or i.v. injection of cocaine. Under a second-order 5-min fixed-interval schedule with 15 intervals per session, rates of responding increased to a maximum and then decreased with increases in the amount of food (from 250 to 4000 mg/presentation) or cocaine (from 25 to 400 micrograms/kg/injection). Cocaine injections maintained higher maximal rates of responding than food presentation. When the brief stimuli were omitted during the 5-min intervals, average rates of responding maintained by cocaine decreased, but those maintained by food presentation did not. The presession administration of cocaine (0.3-1.0 mg/kg i.m.) increased rates of responding maintained by food to about the same level as those maintained by cocaine; these elevated rates did not decrease when the brief stimuli were omitted. Under a second-order 60-min fixed-interval with one interval per session, both food and cocaine maintained relatively high rates of responding even with large amounts of food (7.5-14 g/presentation) or cocaine (375-1500 micrograms/kg/injection). When the brief stimuli were omitted during the 60-min interval, rates of responding maintained by either food or cocaine decreased. Thus, the brief-stimulus presentations were essential for maintaining performance under the second-order 60-min fixed-interval schedule.
松鼠猴在二阶程序下按键，其中每第n次反应会产生2秒的视觉刺激（n反应固定比率；n = 10、20或30）；在经过最短固定时间间隔（二阶t分钟固定间隔；t = 5或60）后，完成固定比率会导致短暂刺激以及食物呈现或静脉注射可卡因。在每个会话有15个间隔的二阶5分钟固定间隔程序下，随着食物量（从每次呈现250毫克增加到4000毫克）或可卡因量（从每次注射25微克增加到400微克/千克）的增加，反应率先上升到最大值然后下降。可卡因注射维持的最大反应率高于食物呈现。当在5分钟间隔期间省略短暂刺激时，可卡因维持的平均反应率下降，但食物呈现维持的反应率没有下降。会前注射可卡因（0.3 - 1.0毫克/千克，肌肉注射）使食物维持的反应率提高到与可卡因维持的反应率大致相同的水平；当省略短暂刺激时，这些升高的反应率没有下降。在每个会话有一个间隔的二阶60分钟固定间隔程序下，即使有大量食物（每次呈现7.5 - 14克）或可卡因（每次注射375 - 1500微克/千克），食物和可卡因都维持相对较高的反应率。当在60分钟间隔期间省略短暂刺激时，食物或可卡因维持的反应率都会下降。因此，短暂刺激呈现对于在二阶60分钟固定间隔程序下维持表现至关重要。
