P300 and uncertainty reduction in a concept-identification task.

The relationship between amplitude of P300, mean amplitude of the slow wave, and uncertainty reduction after (dis)confirmation of hypotheses was studied in a concept-identification task. 16 male university students categorized stimuli according to a conceptual rule (joint denial or exclusion) and rated the confidence that their classification was correct. Three types of feedback were distinguished: confirming (S's categorization was correct), disconfirming (S's categorization was incorrect), and noninformative. EEG was averaged according to type of feedback and confidence rating. Data show the predicted interaction between type of feedback and confidence level. A larger P300 amplitude turned up after confirming feedback when S was less confident than when he was more confident. The reverse was found after disconfirming feedback. The P300 amplitude after noninformative feedback was not influenced by confidence. Mean amplitude of the slow wave showed the same interaction. Results are interpreted in terms of changes in the probability of hypotheses that Ss use to categorize stimuli in a concept-identification task. (40 ref)