Fig. 5.

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 responses during progressive ratio responding for 45-mg Chow A/I pellets in male Wistar rats. Relative frequency histograms (bars) and fit log-Gaussian distributions (lines) (22, 23), show the relation of diet schedule to the duration of IRIs after Chow A/I-reinforced responses. Before diet cycling (left, week 1), distributions were similar between groups, whereas after 5 wk of diet cycling (right), the relative frequency histogram was shifted to the right in diet-alternated rats compared with controls, indicating longer postreinforcement intervals. Nonreinforced intervals were not similarly shifted (not shown). The frequency histogram shows IRIs of between e^-1 and e³ s in duration (0.4–20.1 s) using a bin width of e^0.2 (note ln-scale of x-axis). The time scale shown accounts for a similarly large majority of IRIs in diet-cycled rats (98%) and controls (98%). Tick labels indicate the beginning of the bin. Data were cumulated from 5 sessions during each of weeks 1 and 5.