Fixed interval performance in a large sample of rats (N=113) : interindividual differences

Hundred and thirteen male adult albino rats (Wistar) have successively been submitted to 3 CFR, 3 FI 30, 3 FI 60, 3 FI 90 and 40 FI 120 seconds sessions. The daily sessions lasted in every case 30 minutes. Daily distributions of the Curvature Indice (Fry, Kelleher & Cook, 1960) values showed that the mean value increased up to a stabilization point at the 20th FI 120 seconds session and that the inter-individual differences as estimated by the standard deviation increased progressively throughout the session series. Rank correlations (Kendall Tau t) computed between individual Curvature Index values from adjacent or remote sessions were highly osgnificant and showed that the level of adjustment to the FI schedule early in training has a predictive value.