Schedule of experimental phases.

*The unconditioned stimulus immediately followed CS presentation: 0.15 M LiCl or NaCl (2 mEq/kg, i.p.).**One concentration was tested per session from a range of sucrose, KCl and quinine concentrations.Schedule of experimental phases.非条件刺激（unconditioned stimulus, US）会紧随条件刺激（conditioned stimulus, CS）的呈现后立即给予：采用0.15 M浓度的氯化锂（LiCl）或氯化钠（NaCl），注射剂量为2 mEq/kg，给药方式为腹腔注射（i.p.）。针对蔗糖、氯化钾（KCl）与奎宁的系列浓度梯度，单次实验仅测试其中一种浓度。实验各阶段的时序安排。