Prior attempts to condition a one-celled organism, paramecium, by either classical or instrumental procedures have yielded both positive and negative results. As the results of those studies may be subject to several interpretations other than one indicating learning, it was decided to use a more traditional technique for the present study. This experiment was designed to assess whether aversive electric shock could be used to train paramecia on a brightness discrimination task, a procedure that has been used in animal learning research. The results indicated that such learning may have occurred.

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The idea that rats possess some knowledge about having been incorrect when having previously made an incorrect response is proposed. A matching-to-sample task with a second choice was used to assess the hypothesis. Only if the correct lever was chosen on the second choice was the animal rewarded. Further, the second choice was offered whether the animal was initially correct or incorrect in its first choice, preventing it from "knowing" if it had been correct in its initial decision. If rats possessed some knowledge whether they had been correct or not, then the number of correct second choice responses after an incorrect first one should have been greater than chance. The current experiment provided some evidence that the rats did "know" when its choices were incorrect.

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