Experimental groups and representative sequence of training parameters.

aValues listed for the reinforcement schedules are the average of the programmed values used to determine the time interval (seconds) before a single press yielded reinforcement for the VI groups, or the number of lever presses required to yield reinforcement for the VR groups. From session 7 on, the average ratio was 5 for some VR animals (n = 2 extended training, 11 limited training).
bDrinking solutions were always 10% sucrose (w/v), with either 0% or 10% ethanol (vol/vol), as shown. In the limited training 10S10E groups, some animals received one additional session with 10S before transitioning to 10S10E.
cExtended training continued with the same parameters for an additional 9 sessions, and limited training with no more than 1 additional session, before extinction and retraining (depicted in Figure 1 and described in Behavioral methods).