P300 auditory evoked potentials : semantic categorization in adults

Cortical event-related potentials (ERP) were recorded at Fz, Cz, F3, F4, P3, and P4 scalp sites in 19 normal right-handed females between the ages 20-35. All task stimuli were presented in an oddball (80-20) paradigm, with 20% of the items being infrequent targets. In the first task, subjects made push-button response choices of high and low (target) tones. In the second task, the subject listened to and identified (auditorially and visually) presented words in which target non-kitchen words occurred 20% of the time. In the third task, subjects made push-button response choices to "kitchen" and "non-kitchen" (target) items. Comparisons were made according to P300 amplitude and latency measures. Subsequent analysis of variance for repeated measures and t-tests indicated the following results:

1. Significantly greater frontal P300 amplitude was found for semantic tasks (words tasks).
2. No significant lobe differences were found with regard to P300 amplitude for the Tones task.
3. Greater right than left amplitude was found on all tasks.
4. Greater amplitude was found for Tones as compared to both semantic (word) tasks.
5. In comparing semantic tasks, significantly greater P300 amplitude was found on Task 3 when the subject was given categorization instructions as compared with Task 2 when the subject only identified the words presented.
6. Significantly greater latency was found for semantic tasks in comparison with the Tones task.
7. No significant difference was found in latency between the two word tasks.
8. During Task 3 when the subject was given categorization instruc-tions, greater latency was found for the frontal sites as compared to parietal sites.
Within the confines of the population studied, these results provide information in addition to current literature indicating that the right frontal areas play a major role in semantic categorization. In addition, it would also appear that latency is related to task and site, increasing as relative demands increase in crucial cortical areas.