Envelope-following responses to single and double amplitude modulation: No correlate of modulation masking

Abstract

Magneto- and electroencephalographic (M/EEG) measures of neural responses to speech and other natural sounds provide a noninvasive window into the neural tracking of temporal dynamics of natural sounds. However, the interpretation of these measures and their relation to perception remain unclear. In this study, amplitude modulation (AM) of a low-pass noise carrier (cutoff 4 kHz) was used to measure EEG envelope following responses (EFRs) for two AM rates presented simultaneously or in isolation. The spectral separations between the two AM rates were selected to produce varying degrees of perceptual modulation masking. The AM rates used spanned the range from 8 to 203 Hz, reflecting cortical and subcortical EFR generators. For double-rate AM, the EFRs had two distinct spectral peaks, corresponding to the component AM rates. In all conditions, the peak EFR amplitudes for two simultaneous AM rates did not differ significantly from those presented singly, even when the two rates produced significant perceptual masking. The results show that EEG measures of neural responses synchronized to temporal envelope fluctuations fail to reflect the important perceptual phenomenon of modulation masking. [Work supported by NIH R01 DC012262 (Oxenham) and R01 DC015987 (Wojtczak).]