FIGURE 2.

Operant chamber and training/testing protocols. (A) Operant chamber fitted with tone generator for reinforcing rewarded trials, liquid reward port for saccharin delivery, two retractable levers, and two stimulus lights located above to indicate when a lever was active. (B) Schematic of operant training/testing. Before testing, animals were trained to push levers on both sides of the chamber, and then to push levers twice consecutively for reward (left column). Following this, animals were introduced to probabilistic rewards and reversals, progressively moving to noisier reward contingencies.