During this time, responses at the lever were reinforced by delivery of a 0.2% (w/v) saccharin solution into the drinking receptacle.
Each chamber was equipped with a drinking reservoir (vol. capacity: 0.15 ml) positioned 4 cm above the grid floor in the center of the front panel of the chamber, and 2 retractable levers, located 3 cm (1 to the right and the other to the left) of the drinking receptacle.
Whereas in the Cover conditions, access to the drinking receptacle was blocked by a metal plate, in the No Cover conditions, the drinking receptacle was accessible.
This opening allowed access to the drinking receptacle (Fig. 1, left panel).
Whereas in the Cover conditions, access to the drinking receptacle was covered by an intact metal plate, in different variants of the No Cover conditions, the drinking receptacle was accessible.
In the Cover condition, a metallic plate prevented access to the drinking receptacle, as in the previous experiments.
All rats received 60 min of magazine training, in which they were exposed to sucrose solution from the drinking receptacle.
By contrast, in the new No Cover condition, the cover was intact but moved slightly to the left of the receptacle, rendering the drinking receptacle completely unobstructed.
During this phase, the drinking receptacle in each chamber was covered with a metal plate that had an opening to allow access.
When in the raised position, a small well (0.05 cc) at the end of the dipper arm that contained sucrose solution protruded up into the drinking receptacle.
