Abstract
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.
Highlights
Adverse listening conditions are common in everyday life
The alpha power in the stimulus-free delay interval was dependent on the interplay between task demands and hearing loss (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
Summary
Adverse listening conditions are common in everyday life. Auditory distractions and signal degradations increase demands on attention and working memory (WM; Shinn-Cunningham and Best, 2008). Any degradation of the sensory auditory input requires increased WM involvement to successfully interpret the stimuli (Rönnberg et al, 2008; Stenfelt and Rönnberg, 2009). Auditory processing can be disrupted by internal degradation, such as sensorineural hearing loss (HL). To alleviate this internal degradation of the auditory input, people suffering from HL are typically treated with hearing aids. The purpose of a hearing aid is to amplify the auditory input to make sounds audible and reduce the internal auditory degradation, which theoretically should release WM resources (sometimes referred to as lowered cognitive load; Lunner, 2003). We tested whether HL affects brain signatures of WM involvement in an adverse listening paradigm
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