Positive contrast in instrumental learning from qualitative shift in incentive

Abstract

Rats shifted from food pellets to preferred 32%-sucrose pellets as reinforcers in instrumental (bar-press) learning showed a reliable positive contrast effect when compared to nonshifted control rats given 32%-sucrose pellets throughout training. Rats shifted from 8%-sucrose pellets to 32%-sucrose pellets did not differ from the controls. Positive contrast effects, very rare in the literature but of substantial theoretical importance, should be more readily obtained if sufficiently marked incentive differences are used.