Experience with a category alters hemispheric asymmetries for the detection of anomalies

Previous research with both brain-damaged and neurologically intact individuals suggests that the right cerebral hemisphere (RH) is superior to the left cerebral hemisphere (LH) at detecting anomalies in objects. The current research assesses whether experience with a category is necessary for this RH advantage to emerge. Participants were taught the diagnostic criteria necessary to categorize two fictitious species of animals ("Dleebs" and "Tazes"). After training, participants were given a test in which half of the items were congruent with the diagnostic rules and half of the items were incongruent. Participants were tested on two occasions-once after the initial training session and once after five training sessions. The results demonstrated that experience is required for the RH advantage for anomaly detection to occur. On the first test, reaction times were faster when items were presented to the LH. After 5 days of training, reaction times were faster when items were presented to the RH. This interaction could be due to the fact that participants reported analyzing the items in terms of a series of features during the initial test, but analyzed the items as a configural whole as experience with the category increased.