Principal component analysis of ERP differences related to the meaning of an ambiguous word.

Event-related potentials (ERPs) to the noun and verb meanings of/'led/in the single ambiguous phrase 'it was/'led/' were re-analyzed using principal component analysis (PCA). These data had previously been analyzed by SWDA and reported in this journal. PCA defined 3 meaning-related components, comprising 40.3% of the entire data variance. The N150 component was shown to be larger for the noun meaning than for the verb meaning; the P230 epoch differed in its anterior-posterior distribution according to meaning; and N370 for noun responses was relatively more negative at the right posterior lead and positive at the left anterior. All components taken together, the left anterior lead showed the greatest meaning-related difference. Previous analysis by SWDA had resulted in significant discriminant functions for left hemisphere ERPs, but this analysis did not yield a clear definition of the effects of meaning on specific ERP components or of the scalp distributions of meaning-related components. Thus, while the results of both analyses support the interpretation that the perceived meaning of words has a substantial effect on ERP wave forms, PCA appears to provide the clearest definition of the ERP component effects.