Kreft, H. A. | bioRxiv Science

bioRxiv2020

Effects of age and hearing loss on perceptual and physiological measures of temporal envelope processing and spatial release from speech-on-speech masking

Older adults often experience difficulties understanding speech in adverse listening conditions. These difficulties are partially attributed to auditory temporal-processing deficits associated with aging even in the absence of hearing loss. The aim of this study was to assess effects of age and hearing loss on temporal envelope processing and speech-on-speech masking. Listeners with normal and near-normal hearing across a wide age range (20 to 66 years) were tested using a series of psychophysical (amplitude-modulation detection, gap detection, and interaural-envelope-phase discrimination), physiological (electroencephalographic envelope-following responses), speech perception (spatial release from masking), and cognitive (processing speed) measures. Results showed that: (i) psychophysical measures of monaural and binaural envelope processing and neural measures of envelope processing are not affected by aging after accounting for audiometric hearing loss, (ii) behavioral gap-detection thresholds decline with age, (iii) aging results in a reduction of spatial release from masking, even as speech intensity is amplified in the region of hearing loss, (iv) aging is associated with poorer measures of cognitive function. Although age significantly contributed to a decline in spatial release from speech-on-speech masking, individual differences in envelope processing and in scores from nonauditory cognitive tests used in this study were not significant predictors of speech performance. HighlightsO_LIAge per se does not affect psychophysical and physiological measures of monaural amplitude-modulation processing. C_LIO_LIAge does not affect the ability to detect interaural disparities in envelope timing between the ears. C_LIO_LIGap detection thresholds degrades with age even after hearing thresholds are statistically accounted for. C_LIO_LIAge, independent of hearing thresholds, can substantially reduce spatial release from masking. C_LIO_LICognitive ability declines with age. However, such declines do not necessarily cause deficits in spatial release from masking. C_LI

physiology↗

bioRxiv2018

Perception of frequency modulation is mediated by cochlear place coding

Natural sounds convey information via frequency and amplitude modulations (FM and AM). Humans are acutely sensitive to the slow rates of FM that are crucial for speech and music. This sensitivity has been thought to rely on precise stimulus-driven auditory-nerve spike timing (time code), whereas a coarser code, based on variations in the cochlear place of stimulation (place code), represents faster FM. Here we test this longstanding theory in listeners with normal and impaired hearing, resulting in widely varying place-coding fidelity. Contrary to predictions, FM detection thresholds at slow and fast rates are highly correlated and closely related to the fidelity of cochlear place coding. We support this conclusion with additional data showing that place-based coding degrades at high modulation rates and in high spectral regions in ways that were previously interpreted as reflecting the limits of fine neural timing. The results suggest a unitary place-based neural code for FM.

neuroscience↗