Cochlear contributions to behavioral and neurophysiological measures of low-frequency temporal envelope processing

The auditory cortex reliably tracks temporal envelopes of speech and non-speech stimuli. Because of that, magneto-/electroencephalographic (M/EEG) based metrics of temporal envelope tracking have been used as neurophysiologic markers of the integrity of temporal processing. These metrics typically show enhanced neural responses to low-frequency envelopes in older compared to younger adults. Enhanced cortical tracking has been explained in terms of age-related loss of inhibitory processes and/or a greater reliance of older adults on cognitive processes due to degraded acoustic information. In this study, we tested the hypothesis that age-related changes in cochlear nonlinearity may, at least in part, contribute to enhanced low-frequency envelope EEG responses. Loss of cochlear nonlinearity was estimated from the growth of distortion-product otoacoustic emissions (DPOAEs). Behavioral measures of amplitude-modulation (AM) detection and EEG envelope-following responses (EFRs) were measured in older and younger adults with normal hearing using an 8-Hz sinusoidal AM applied to a noise carrier low-pass filtered at 4 kHz. A highpass noise was used to mask responses from basal sites of the cochlea. Preliminary data show that reduced cochlear nonlinearity was associated with improved AM detection and increased EFR magnitudes in older compared to younger adults. [Work supported by NIH R01 DC 021362 (Wojtczak).]