DISTRIBUTIONS OF THE ND AND P300 IN A NORMAL SAMPLE

To obtain objective criteria for assessing the attentional and cognitive functioning of psychiatric populations, we attempted to standardize values of two components in Event-Related Potentials (ERPs), namely the attention-related negative potential (Nd) and the P300, in normal populations. The study consisted of 100 healthy volunteers (50 females, 50 males) who were given the task of making dichotic syllable discriminations requiring key-press responses. Their ages ranged between 18 and 59 years (mean +/- S.D., 32.3 +/- 11.3 years). Nd was found to be maximum in the Fz region, P300 being maximum in the Pz region. The means and standard deviations of Nd and P300 areas in their maximum regions were 554.1 +/- 307.8 muV ms and 2148.5 +/- 1248.5 muV ms, respectively. The transformation plot for symmetry indicated the suitable power of transformation to be 1/2 for both Nd and P300 distributions. After being transformed into square-root values, the distribution patterns of Nd and P300 areas were examined. When the lower limit of normal values was tentatively assigned to mean - 2 S.D. using square-root transformed data for both Nd and P300, 97% of the subjects were found to display values above the lower normal limit for Nd, and 98% for the P300. Neither, Nd nor P300 areas correlated with age, while P300 latencies displayed a weak positive correlation with age. Females displayed relatively larger values than males for Nd and P300 areas and P300-peak amplitudes. However, the differences between females and males were not statistically significant. Females and males showed nearly equal P300-peak latencies.