Fig.1.

Diagram of the Behavioral Procedure (see “Behavioral Procedure” section for details). Sessions consisted of 60 choice cycles; each choice cycle was comprised of an initial (choice) link, during which choice responses were made on either lever, and a terminal (outcome) link, which provided the consequences for each choice. Each choice cycle began with a press of the rear lever. (a) Shows large-left sessions, in which the larger reinforcer was associated with the left lever and the smaller reinforcer was associated with the right lever; (b) shows large-right sessions, in which the larger reinforcer was associated with the right lever and the smaller reinforcer was associated with the left lever. Large-left and Large-right sessions alternated every 5 sessions; rats learned which sides were associated with the larger and smaller reinforcers based upon the outcomes of their choices. Rectangles indicate levers and circular starbursts indicate lever lights. Unfilled and filled rectangles indicate when a lever was extended (available) and retracted (unavailable), respectively; unfilled and filled starbursts indicate when a lever light was on and off, respectively. The lever light associated with the larger reinforcer blinked during the initial link and during its associated terminal link (indicated by striped starbursts).