Status of unchosen objects in discrimination learning by monkeys

Monkeys were given a mixture of discrimination training and choice trials. The choice involved a previously unchosen object selected from a trial where the chosen object had been rewarded vs. a previously unchosen object selected from a trial where the chosen object had not been rewarded. On these nondifferentially rewarded choice trials, monkeys exhibited a small but consistent preference for the previously unchosen object that had been associated with a rewarded outcome. The results showed that the outcome of a discrimination trial is associated to varying degrees with both the chosen and unchosen objects, but the mechanism by which unchosen objects are associated with trial outcomes remains uncertain.