Effects of spectral degradation on the cortical tracking of the speech envelope

Abstract:

During speech listening, recurring patterns of neural activity become temporally coupled to stimulus features, such as the speech envelope. This cortical tracking can be measured using electroencephalography (EEG). Quantifying speech-brain coupling (e.g., as a correlation coefficient) sheds light on the neurobiological processes underlying perception and holds promise as an objective measure, particularly for clinical populations such as cochlear implant (CI) users. How spectral degradation associated with CI stimulation affects cortical tracking, however, remains unclear. In this EEG study, we simulate CI listening using vocoded speech with and without current spread, a realistic complication of CI stimulation. We find no effect of either vocoding or current spread on cortical tracking, despite differences in subjective reports of speech comprehension and implicit behavioural measures. We conclude that, when speech is intelligible, cortical tracking is robust to spectral degradation.