Negative and positive incentive contrast effects with saccharine versus sucrose

Forty male white rats received 19 sessions of bar press training with sucrose (16% or 4%) as reward followed by a shift from 4% to 16% and from 16% to 4%. Three dependent measures indicated positive and negative contrast effects. In Experiment II, 70 male white rats received 14 sessions of bar press training with (1.2%, 1%, .10%, or .01%) saccharine, and water followed by a shift from 1.2% to .10%, 1.2% to .01%, 1 to .1%, and .10% to .01%. Three of the four measures indicated negative contrast effects. In Experiment III, 40 male white rats experienced 16 sessions of bar press training with 1%, .10%, .05%, or .01% of saccharine followed by an increase from .1%, to 1%, .05% to 1%, and .01% to 1%. Three of the measures indicated positive contrast effects. Confounding inherent in the use of solid food or sucrose did not appear to account for negative and positive incentive contrast effects.