P3 latency jitter assessed using 2 techniques. I. Simulated data and surface recordings in normal subjects.

Latency variability measurement using cross-correlational techniques has the drawback of alignment to background noise not related to ERP activity. We compared latency jitter estimation in simulated and real P3 recordings using Woody's algorithm and a non-cross-correlational technique, the maximum likelihood technique (MLT). Simulated ERPs (with introduced latency jitter) were generated using either a 1/2 cycle 2 Hz sine wave or an averaged P3 ERP with 1 of 3 added noise types in 5 signal to noise ratios (SNRs): (i) white noise; (ii) a 10 Hz sine wave; (iii) a 7.5 Hz sine wave. Jitter measurement accuracy was assessed using mean square error (MSE) for 1 iteration of the Woody method and each of 4 iterations of the MLT. Lowest MSEs occurred for higher SNRs and 1 iteration of the MLT. The MLT and Woody method were applied to P3 ERPs of 13 subjects with SNRs greater than 0.4 P3 latency jitter was significantly lower for the MLT. Latency jitter (both methods) did not differ between homologous electrodes and was highest in posterior electrodes. In the latency corrected ERP data of subjects with persistent alpha activity periodic components occurred in the Woody corrected average (not seen in the conventional or the MLT corrected averages). Our data indicate that the MLT is the more accurate method for determining latency jitter.