Learning as a function of programmed and experienced delays to reinforcement The imposition of response-reinforcer delays systematically retarded the acquisition of free-operant instrumental responding, and this relationship was altered in AcbC-lesioned rats, even allowing for differences in experienced response-collection delays. (a) The rate of responding on the active lever in session 10 is plotted against the programmed response-reinforcer delay. AcbC-lesioned rats responded more than shams at zero delay (* p = .013), but less than shams at 10 s (* p = .049) and 20 s delay (*** p = .001). (b) Responding on the active lever in session 10 plotted against the experienced response-to-reinforcer collection delays for sessions 1–10 (vertical error bars: SEM of the square-root-transformed number of responses in session 10; horizontal error bars: SEM of the experienced response-collection delay, calculated up to and including that session). The gradients of the two lines differed significantly (### p = .001; see text), indicating that the relationship between experienced delays and responding was altered in AcbC-lesioned rats.