Differential outcomes facilitate same/different concept learning.

Commonly recognized, the training procedure one employs often affects the results they obtain. Here, we demonstrate for the first time that abstract-concept learning is affected by employing a differential-outcomes procedure. The differential-outcome effect has been shown to occur for item-specific strategies but has not been established for relational strategies. To test whether different-outcome expectancies can facilitate a relational strategy, eight pigeons were trained and tested in a two-item same/different task with pictures. After pecking an upper picture, they pecked a lower picture if the pictures were the same or a white rectangle if the pictures were different. Two groups of pigeons were rewarded with either different outcomes (sounds and food amounts) or same outcomes. Both groups were trained to criterion with successively larger picture sets (8-1,024 items) and were transfer tested with novel pictures following each acquisition. With the smallest training sets, neither group showed any novel-stimulus transfer. But after acquiring the task with 32 pictures, the different-outcomes group responded more accurately to novel pictures than the same-outcome group. As the training set-size increased, both groups' transfer performance converged and became equivalent to training performance. These results show for the first time that training with different outcomes facilitates abstract-concept learning.