Neurophysiological correlates of meaningful and nonmeaningful sentence processing

Event related potentials (ERPs) were utilized to investigate the influences of sex and presentation on meaningful and nonmeaningful sentence processing. Amplitude and latency values were recorded from a central (Cz) and left parietal (P3) electrode location beginning with the onset of the last (Key) word or nonsense syllable in the sentence. The ERPs were recorded for approximately 1000 msec, and peaks were recorded within three different time windows: 52.5 to 170.0 msec (N100), 172.5 to 285.0 msec (P200) and 290.0 to 580.0 msec (P300). Two of the amplitude measures, P200 and P300, were referenced to the N100 component by measuring the peak-to-peak amplitudes resulting in N100P200 and N100P300 measures. Peak latencies corresponding to the N100, P200, and P300 amplitudes were also computed.

Seven young female adults and seven young male adults listened to two identical presentations of ten randomized recordings of each of the ten stimulus sentences (200 total sentences). The ten different sentences consisted of five pairs with each semantically inappropriate sentence differing from its cognate sentence in the final (Key) word or element. Two of the semantically inappropriate sentences contained real words inappropriately placed in the final position. The other three (phonemic) semantically inappropriate sentences contained a nonsense CVC which differed from its cognate sentence in the final phoneme of the CVC.

Subsequent analyses of variance and planned comparison testing indicated the following results:

1. Females manifested significantly more positive N100P300 amplitudes than males at Cz and P3. These amplitude differences between females and males were also statistically significant at N100 and N100P200 for Cz, but not for P3.

2. Semantically inappropriate sentences were generally significantly more negative (N100) or more positive (N100P200, N100P300) than the semantically appropriate sentences at Cz and P3. 3. N100P200 amplitude was significantly more positive for the semantically inappropriate sentences with the real words tall and teeth for Cz and P3.

4. N100P300 amplitude reflected statistically significant differences between the phonemic-semantically inappropriate and phonemic semantically appropriate sentences.

5. Latencies were generally shorter for the semantically in appropriate sentences, however, these differences were not as pronounced nor as consistent as the amplitude differences.

6. Although there were no significant differences in the main effect Presentation, ERPs for the first presentation generally manifested more positive waveforms than did the second presentation.