Event-related potentials recorded from the scalp and nasopharynx. II. N2, P3 and slow wave.

Scalp and nasopharyngeal recordings of the N2, P3 and slow wave components were compared in a target-detection task. The effects of probability, interstimulus interval, intensity, discrimination difficulty, attention, stimulus omission and modality were evaluated. Waves of opposite polarity to the scalp N2 and P3 components were recorded in the nasopharynx. The scalp and nasopharyngeal N2 components showed different patterns of variation across experimental conditions. These findings indicate that there are two different cerebral processes occurring at the latency of the scalp N2. The scalp and nasopharyngeal P3 components consistently covaried across conditions, suggesting a single underlying process. The slow wave was observed only in the scalp recordings.