Autism spectrum disorders (ASD) are associated with impaired attentional set shifting, which may reflect enhanced perseverative responding, enhanced learned irrelevance, and/or reduced novelty processing. We assessed the contribution of these potential error sources in ASD adults. A total of 17 ASD and 19 matched comparison individuals first solved a discrimination learning task. Thereafter, the participants faced three types of attentional shift, specifically designed to isolate the effect of the three possible error sources. ASD participants made more errors than comparison individuals in a shift implying a choice between a novel relevant stimulus attribute and a familiar attribute that was previously relevant but now irrelevant. However, they made fewer errors in a shift involving a choice between a novel irrelevant attribute and a familiar, previously irrelevant but now relevant attribute. The results in combination suggest that the performance difference, at least in the present shift task, is caused by reduced novelty processing in ASD participants.