4 groups of 32 female Ss each were compared on a 2-category concept-identification task with 6 stimulus dimensions. At the beginning of the task, 1 group received 6 trials on which E said "right" regardless of S's responses, 1 group received 6 "wrongs," and 1 group received 6 trials on which E said nothing. Another group received no prior trials. The group given 6 "rights" was significantly inferior to the other 3 groups in terms of trial of last error and learning rate parameters of the all-or-none model. The other 3 groups did not differ significantly from one another. It was suggested that noncontingent "rights" contribute maximally to random reinforcement effects.

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