Reversal learning measures reveal D2R-/- mice emit significantly more errors of commission but not errors of omission than D2R+/+ mice. Response patterns (mean + standard error) by D2R-/- mice are more suggestive of stimulus bound perseveration and not extinction. D2R-/- mice committed significantly more errors of commission (A) than D2R+/+ mice (*p < 0.01), but no differences in errors of omission (B) were observed between genotypes (p > 0.6).