Implicit learning of the one-back reinforcement matching-mismatching task by pigeons.

Humans can learn tasks explicitly, as they can often describe the rules they have used to learn the task. Animals, however, are thought to learn tasks implicitly (i.e., purely associatively). That is, they gradually learn the correlation or association between the stimulus (or response) and the outcome. Both humans and pigeons can learn matching, where a sample stimulus indicates which one of two stimuli matches the sample. The 1-back reinforcement task is a difficult version of matching in which a correct response on trial N is rewarded only following a response on trial N + 1 (independent of the response on trial N + 1), and the correct response on trial N + 1 indicates whether a reward will occur on trial N + 2, and so forth. Humans do not appear to be able to learn the 1-back rule. Pigeons, however, do show 1-back reinforcement learning, and they appear to do so implicitly by gradually learning the correlation between their response on one trial and the outcome on the next trial (because all other relations are uncorrelated with the outcome). They learn the task slowly and to a level below what would be expected had they learned it explicitly. The present results, together with research with humans, suggest that there are times when human explicit learning may interfere with the ability of humans to learn. Pigeons, however, are not "distracted" by attempts at explicit learning, and thus they are able to learn this and other similar tasks..