Envelope following responses to Schroeder-phase harmonic stimuli

Recent studies suggest that peripheral nonlinearities only partially account for the envelope-following response (EFR) recorded at the scalp, with additional contributions from broadly tuned neurons in the central nervous system. The present study investigated this by measuring EFR to low and high-frequency stimuli designed to (1) optimize within-channel phase synchrony to produce maximal envelope modulation depth on the basilar membrane, or (2) optimize phase synchrony across multiple frequency channels to maximize envelope-related activity arising in the central nervous system. EFR was recorded in normal-hearing listeners using Schroeder-phase stimuli with harmonic components constrained to low and high-frequency ranges, as well to multi-frequency sinusoidally amplitude modulated tones as a function of component phase. Estimates of basilar membrane phase curvature varied across individuals. Response amplitudes and phase-locking values for the EFR varied as a function of carrier frequency range and compo...