Fig. 4.

Effects of repeated cycles of 5-day access to chow alternated by 2-day access to either Chow A/I (Chow A/I / Chow A/I, n = 14) or highly preferred chocolate-flavored sugary diet (Chow A/I / Preferred, n = 15) on the duration of interresponse intervals (IRIs) following reinforced (A) or nonreinforced responses (B) during progressive ratio responding for 45-mg Chow A/I pellets in male Wistar rats. Values are presented as means ± SE. IRI durations were ln-transformed for statistical analysis, and bars represent back-transformed values. Data were cumulated from 5 sessions during each of weeks 1 and 5. *Significantly different from Chow A/I / Chow A/I, P < 0.05, ***P <0.001.