Age-Related Deficits in Electrophysiological and Behavioral Measures of Binaural Temporal Processing.

Tess K Koerner,Curtis J Billings,Frederick J Gallun,Ramesh Kumar Muralimanohar

doi:10.3389/fnins.2020.578566

Tess K Koerner, Curtis J Billings + Show 2 more

Open Access

https://doi.org/10.3389/fnins.2020.578566

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Abstract

Binaural processing, particularly the processing of interaural phase differences, is important for sound localization and speech understanding in background noise. Age has been shown to impact the neural encoding and perception of these binaural temporal cues even in individuals with clinically normal hearing sensitivity. This work used a new electrophysiological response, called the interaural phase modulation-following response (IPM-FR), to examine the effects of age on the neural encoding of interaural phase difference cues. Relationships between neural recordings and performance on several behavioral measures of binaural processing were used to determine whether the IPM-FR is predictive of interaural phase difference sensitivity and functional speech understanding deficits. Behavioral binaural frequency modulation detection thresholds were measured to assess sensitivity to interaural phase differences while spatial release-from-masking thresholds were used to assess speech understanding abilities in spatialized noise. Thirty adults between the ages of 35 to 74 years with normal low-frequency hearing thresholds were used in this study. Data showed that older participants had weaker neural responses to the interaural phase difference cue and were less able to take advantage of binaural cues for speech understanding compared to younger participants. Results also showed that the IPM-FR was predictive of performance on the binaural frequency modulation detection task, but not on the spatial release-from-masking task after accounting the effects of age. These results confirm previous work that showed that the IPM-FR reflects age-related declines in binaural temporal processing and provide further evidence that this response may represent a useful objective tool for assessing binaural function. However, further research is needed to understand how the IPM-FR is related to speech understanding abilities.

Highlights

Accurate processing of binaural information is key to sound source localization and the detection of target signals in background noise
The interaural phase modulation-following response (IPM-FR) response peak at 6.8 Hz and subsequent harmonics are absent in the diotic control conditions for both stimuli, but auditory steady-state response (ASSR) are still observed at the 40.8- and 81.6-Hz amplitude modulated (AM) rates (Figures 5C,D, respectively)
Given that the main purpose of this study was to examine the effects of age on binaural temporal processing using the IPM-FR and to examine relationships between neural responses and behavioral performance, individual neural responses were used for all statistical analyses

Summary

Introduction

Accurate processing of binaural information is key to sound source localization and the detection of target signals in background noise. Aging and Neural IPD Encoding use these binaural IPD cues is dependent on accurate neural firing to the rapid fluctuations in signal amplitude over time, termed temporal fine structure, and the accurate comparison of these temporal cues between the ears. Recent research has shown that aging can impact the ability to process binaural temporal fine structure information independent of hearing loss, resulting in reduced IPD sensitivity (Ross et al, 2007a; Grose and Mamo, 2010, 2012b; Hopkins and Moore, 2011; Gallun et al, 2013, 2014; Papesh et al, 2017; Füllgrabe and Moore, 2018; Vercammen et al, 2018) and deficits understanding speech in background noise (Füllgrabe et al, 2015; Papesh et al, 2017). While the exact cause of this age-related decline in temporal processing is unknown, disruptions in neural synchrony, a slowing of neural activity, a loss of cochlear afferent synapses, deficits in the central integration of binaural information, and/or deficits in the central encoding of binaural information have been known to occur with aging (He et al, 2008; Grose and Mamo, 2010; Ruggles et al, 2012; King et al, 2014; Shaheen et al, 2015; Whiteford et al, 2017; Parthasarathy and Kujawa, 2018; Wu et al, 2019)

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