Supplementary knowledge of results.

Children learned to respond differentially to four tones when correct responses were indicated by re-sounding the tone and flashing a signal lamp (simple knowledge of results). Correct responses were then made to advance a display counter. With this procedure, rate of response increased, but accuracy decreased. Mild punishment-points subtracted from the count-was then arranged for incorrect responses. Accuracy returned to or above its previous level. Response rate tended to remain above its initial level. These results indicate that when supplementary reinforcers are employed, precise contingencies must be arranged to ensure desired behavior.