Adult vernier thresholds do not increase with age; vernier bias does.

Vernier acuity and vernier bias were examined in persons aged 20 to 79 years using a method of adjustments. Vernier bias (mean error) showed a sharp increase between 35 and 45. Vernier acuity (standard deviation or precision of alignment) did not vary significantly with age. These different results indicate the importance of separate evaluation of acuity and bias. Vernier acuity is little affected by minor optical changes that occur with age. Therefore, normal vernier acuity in older persons suggests that the neural substrates which underlie fine-grain discrimination of object location are unaffected by aging over the range investigated.