Previous work has shown that noncontingent reward, presented concurrently with contingent reward, has a detrimental effect on learning response‐reward contingencies and the motivation to respond. The present experiment sought to offer an explanation for those results. Introductory psychology students earned points on a counter (reward) by striking the correct one of 10 keys on a variable ratio schedule. In addition to this contingent reward, three other groups received noncontingent reward under one of three conditions: (a) free reward, which was independent of any aspect of the subject's behaviour, (b) free reward, which was signalled, and (c) reward which was response‐dependent but irrelevant to the contingency detection problem. The results showed that the problem‐irrelevant property of noncontingent reward disrupts learning. Two possible explanations for noncontingent reward decreasing the tendency to respond are prof