Determining latency and amplitude for multiple peaked P300 waveforms.

The P300 is characterized by a large positive peak occurring approximately 300 msec post stimulus onset. When a single peak is present, the P300 latency is easily identifiable. However, in cases where the P300 waveform is broadly or multiply peaked, ambiguity exists when attempting to determine the latency of the waveform. Amplitude, while less ambiguous, has also been variously measured as baseline to peak, or peak-to-peak, using either N200 or N300 as the trough. The present study was undertaken to evaluate a method for precisely and consistently determining the latency and amplitude characteristics of the P300 waveform. Three independent raters examined 40 records to determine P300 latency and amplitude according to prescribed criteria. Results indicated that the suggested techniques yield good inter-rater agreement on the latency and amplitude characteristics of the P300 waveform regardless of P300 morphology.