Fig. 2.

Log reinforcement magnitude ratios (L/R), indicated by unfilled squares, and initial-link response ratios, indicated by filled circles, for three representative rats over the 20 baseline sessions prior to the initiation of the regimen of oxycodone administration. Saline was administered on the 5^th, 10^th, 15^th, and 20^th of these sessions (i.e., the last session of each 5-session block). Sensitivity to reinforcement magnitude (S_A) and bias (log b) for each rat, determined using Equation 1, is indicated. Rat W22 (a) showed the highest sensitivity, Rat W20 (b) showed an intermediate sensitivity, and Rat W21 (c) showed the lowest sensitivity, compared to all rats in the study.