Contribution of Spectrotemporal Features on Auditory Event-Related Potentials Elicited by Consonant-Vowel Syllables

Abstract

To determine the influence of spectrotemporal properties of naturally produced consonant-vowel syllables to speech-evoked auditory event-related potentials (ERPs) for stimuli with very similar or even identical wide-band envelopes. Speech-evoked ERPs may be useful for validating the neural representation of speech. Speech-evoked ERPs were obtained from 10 normal-hearing young adults in response to the syllables /da/ and /ta/. Both monosyllables were obtained from ongoing speech. They have quite similar wide-band envelopes, and they mainly differ in the spectrotemporal content of the consonant parts. Additionally, each stimulus derivatives were investigated with (1) isolated consonant part ("consonant stimulus"), (2) isolated vowel part ("vowel stimulus"), and (3) removed spectral information but identical wide-band envelope. Latencies and amplitudes of the N1 and P2 components were determined and analyzed. ERPs in response to the naturally produced /ta/ syllable had significant shorter N1 and P2 latencies and larger amplitudes than ERPs in response to /da/. Similar differences were observed for the ERPs evoked by the consonant stimuli alone. For the vowel stimuli and stimuli with removed spectral information, no significant differences were observed. In summary, differences between the ERPs of /da/ and /ta/ corresponded to the distinct spectrotemporal content in the consonant parts of the original consonant-vowel (CV) syllables. The study shows that even small differences in spectrotemporal features of speech may evoke different ERPs, despite very similar or even identical wide-band envelopes. The results are consistent with a model that ERPs evoked by short CVs are an onset response to the consonant merged with an acoustic change complex evoked by the vowel part. However, all components appear as one P1-N1-P2 complex. The results may be explained by differences in the narrow-band envelopes of the stimuli. Therefore, this study underlines the limitations of the wide-band envelope in explaining speech-evoked ERPs. Additionally, the results of this study are of special interest for clinical application since some of the ERP parameter differences, as the N1 latency, are present not only in the ERPs of each single subject but also in the group mean value of all N1 latencies. Thus, presented ERP measurements in response to CVs might be used for identification of potential problems in phoneme differentiation caused by spectrotemporal analysis problems.