Hearing loss impacts neural alpha oscillations under adverse listening conditions.
Degradations in external, acoustic stimulation have long been suspected to increase the load on working memory (WM). One neural signature of WM load is enhanced power of alpha oscillations (6-12 Hz). However, it is unknown to what extent common internal, auditory degradation, that is, hearing impairment, affects the neural mechanisms of WM when audibility has been ensured via amplification. Using an adapted auditory Sternberg paradigm, we varied the orthogonal factors memory load and background noise level, while the electroencephalogram was recorded. In each trial, participants were presented with 2, 4, or 6 spoken digits embedded in one of three different levels of background noise. After a stimulus-free delay interval, participants indicated whether a probe digit had appeared in the sequence of digits. Participants were healthy older adults (62-86 years), with normal to moderately impaired hearing. Importantly, the background noise levels were individually adjusted and participants were wearing hearing aids to equalize audibility across participants. Irrespective of hearing loss (HL), behavioral performance improved with lower memory load and also with lower levels of background noise. Interestingly, the alpha power in the stimulus-free delay interval was dependent on the interplay between task demands (memory load and noise level) and HL; while alpha power increased with HL during low and intermediate levels of memory load and background noise, it dropped for participants with the relatively most severe HL under the highest memory load and background noise level. These findings suggest that adaptive neural mechanisms for coping with adverse listening conditions break down for higher degrees of HL, even when adequate hearing aid amplification is in place.
Eriksholm Research Centre, Snekkersten Denmark ; Technical Audiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping Sweden ; Linnaeus Centre HEAD, Swedish Institute for Disability Research, Linköping University, Linköping Sweden.
Eline B
EB
Petersen
International Max Planck Research School on Neuroscience of Communication, Leipzig Germany ; Max Planck Research Group "Auditory Cognition", Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig Germany.
Malte
M
Wöstmann
Max Planck Research Group "Auditory Cognition", Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig Germany.
Jonas
J
Obleser
Technical Audiology, Department of Clinical and Experimental Medicine, Linköping University, Linköping Sweden ; Linnaeus Centre HEAD, Swedish Institute for Disability Research, Linköping University, Linköping Sweden.
Stefan
S
Stenfelt
Eriksholm Research Centre, Snekkersten Denmark ; Linnaeus Centre HEAD, Swedish Institute for Disability Research, Linköping University, Linköping Sweden.
Thomas
T
Lunner
alpha oscillations; cognition; hearing aid; hearing loss; working memory