Stimulus enhancement: Controls for social facilitation and local enhancement

In two experiments, magazine-trained observer rats were given access to a p air of levers and allowed to make 50 reinforced responses immediately after the left or the right lever had been pressed 100 times for food reward by a conspecific demonstrator. In Experiment 1, where observers were rewarded for responses on either lever, those that had been able to see their demons trators responding showed a response bias in favor of the demonstrator's le ver, while rats that had been separated from their demonstrators by a metal screen did not. In Experiment 2, each observer saw a "viewed demonstrator" responding on one lever and was tested, with reinforcement for responses o n the viewed demonstrator's lever or on the other manipulandum in a second chamber where a ''box demonstrator'' had just finished responding. Observer s rewarded for responding on the same lever as the viewed demonstrator (Gro up SAME) showed better discrimination at the beginning of the test session than observers rewarded for responses on the other lever (Group DIFFERENT). Within Group SAME, rats whose box demonstrator had responded on the reinfo rced lever showed better discrimination than those whose box demonstrator r esponded on the nonreinforced lever, but thr:reverse was true in Group DIFF ERENT. Both experiments provide evidence of stimulus enhancement unconfound ed by social facilitation and local enhancement, and the latter suggests th at demonstrator-deposited scent cues can facilitate discrimination via loca l enhancement or on the basis of their sensory properties alone. (C) 2000 A cademic Press.