Tine Goossens

Aging Affects Neural Synchronization to Speech-Related Acoustic Modulations

As people age, speech perception problems become highly prevalent, especially in noisy situations. In addition to peripheral hearing and cognition, temporal processing plays a key role in speech perception. Temporal processing of speech features is mediated by synchronized activity of neural oscillations in the central auditory system. Previous studies indicate that both the degree and hemispheric lateralization of synchronized neural activity relate to speech perception performance. Based on these results, we hypothesize that impaired speech perception in older persons may, in part, originate from deviances in neural synchronization. In this study, auditory steady-state responses that reflect synchronized activity of theta, beta, low and high gamma oscillations (i.e., 4, 20, 40, and 80 Hz ASSR, respectively) were recorded in young, middle-aged, and older persons. As all participants had normal audiometric thresholds and were screened for (mild) cognitive impairment, differences in synchronized neural activity across the three age groups were likely to be attributed to age. Our data yield novel findings regarding theta and high gamma oscillations in the aging auditory system. At an older age, synchronized activity of theta oscillations is increased, whereas high gamma synchronization is decreased. In contrast to young persons who exhibit a right hemispheric dominance for processing of high gamma range modulations, older adults show a symmetrical processing pattern. These age-related changes in neural synchronization may very well underlie the speech perception problems in aging persons.

Masked speech perception across the adult lifespan: Impact of age and hearing impairment.

&NA; As people grow older, speech perception difficulties become highly prevalent, especially in noisy listening situations. Moreover, it is assumed that speech intelligibility is more affected in the event of background noises that induce a higher cognitive load, i.e., noises that result in informational versus energetic masking. There is ample evidence showing that speech perception problems in aging persons are partly due to hearing impairment and partly due to age‐related declines in cognition and suprathreshold auditory processing. In order to develop effective rehabilitation strategies, it is indispensable to know how these different degrading factors act upon speech perception. This implies disentangling effects of hearing impairment versus age and examining the interplay between both factors in different background noises of everyday settings. To that end, we investigated open‐set sentence identification in six participant groups: a young (20–30 years), middle‐aged (50–60 years), and older cohort (70–80 years), each including persons who had normal audiometric thresholds up to at least 4 kHz, on the one hand, and persons who were diagnosed with elevated audiometric thresholds, on the other hand. All participants were screened for (mild) cognitive impairment. We applied stationary and amplitude modulated speech‐weighted noise, which are two types of energetic maskers, and unintelligible speech, which causes informational masking in addition to energetic masking. By means of these different background noises, we could look into speech perception performance in listening situations with a low and high cognitive load, respectively. Our results indicate that, even when audiometric thresholds are within normal limits up to 4 kHz, irrespective of threshold elevations at higher frequencies, and there is no indication of even mild cognitive impairment, masked speech perception declines by middle age and decreases further on to older age. The impact of hearing impairment is as detrimental for young and middle‐aged as it is for older adults. When the background noise becomes cognitively more demanding, there is a larger decline in speech perception, due to age or hearing impairment. Hearing impairment seems to be the main factor underlying speech perception problems in background noises that cause energetic masking. However, in the event of informational masking, which induces a higher cognitive load, age appears to explain a significant part of the communicative impairment as well. We suggest that the degrading effect of age is mediated by deficiencies in temporal processing and central executive functions. This study may contribute to the improvement of auditory rehabilitation programs aiming to prevent aging persons from missing out on conversations, which, in turn, will improve their quality of life. HighlightsIn normal‐hearing adults, masked speech perception declines by middle age.The impact of hearing impairment is alike for young, middle‐aged, and older adults.Impacts of age and hearing impairment depend on the cognitive load of the noise.Hearing loss is the main cause of impaired speech perception in energetic masking.Age is mainly a degrading factor in cognitively demanding, informational masking.

Spatiotemporal reconstruction of auditory steady-state responses to acoustic amplitude modulations: potential sources beyond the auditory pathway.

Abstract Investigating the neural generators of auditory steady‐state responses (ASSRs), i.e., auditory evoked brain responses, with a wide range of screening and diagnostic applications, has been the focus of various studies for many years. Most of these studies employed a priori assumptions regarding the number and location of neural generators. The aim of this study is to reconstruct ASSR sources with minimal assumptions in order to gain in‐depth insight into the number and location of brain regions that are activated in response to low‐ as well as high‐frequency acoustically amplitude modulated signals. In order to reconstruct ASSR sources, we applied independent component analysis with subsequent equivalent dipole modeling to single‐subject EEG data (young adults, 20–30 years of age). These data were based on white noise stimuli, amplitude modulated at 4, 20, 40, or 80 Hz. The independent components that exhibited a significant ASSR were clustered among all participants by means of a probabilistic clustering method based on a Gaussian mixture model. Results suggest that a widely distributed network of sources, located in cortical as well as subcortical regions, is active in response to 4, 20, 40, and 80 Hz amplitude modulated noises. Some of these sources are located beyond the central auditory pathway. Comparison of brain sources in response to different modulation frequencies suggested that the identified brain sources in the brainstem, the left and the right auditory cortex show a higher responsiveness to 40 Hz than to the other modulation frequencies.

Electrophysiological and Behavioral Evidence of Reduced Binaural Temporal Processing in the Aging and Hearing Impaired Human Auditory System

A person’s ability to process temporal fine structure information is indispensable for speech understanding. As speech understanding typically deteriorates throughout adult life, this study aimed to disentangle age and hearing impairment (HI)-related changes in binaural temporal processing. This was achieved by examining neural and behavioral processing of interaural phase differences (IPDs). Neural IPD processing was studied electrophysiologically through steady-state activity in the electroencephalogram evoked by periodic changes in IPDs over time, embedded in the temporal fine structure of acoustic stimulation. In addition, behavioral IPD discrimination thresholds were determined for the same stimuli. To disentangle potential effects of age from those of HI, both measures were applied to six participant groups: young, middle-aged, and older persons, with either normal hearing or sensorineural HI. All participants passed a cognitive screening, and stimulus audibility was controlled for in participants with HI. The results demonstrated that HI changes neural processing of binaural temporal information for all age-groups included in this study. These outcomes were revealed, superimposed on age-related changes that emerge between young adulthood and middle age. Poorer neural outcomes were also associated with poorer behavioral performance, even though the behavioral IPD discrimination thresholds were affected by age rather than by HI. The neural outcomes of this study are the first to evidence and disentangle the dual load of age and HI on binaural temporal processing. These results could be a valuable first step toward future research on rehabilitation.

The association between hearing impairment and neural envelope encoding at different ages

Hearing impairment goes with speech perception difficulties, presumably not only because of poor hearing sensitivity but also because of altered central auditory processing. Critical herein is temporal processing of the speech envelope, mediated by synchronization of neural activity to the envelope modulations. It has been suggested that hearing impairment is associated with enhanced sensitivity to envelope modulations which, in turn, relates to poorer speech perception. To verify this hypothesis, we performed a comparative electrophysiological study in hearing-impaired (HI) and normal-hearing (NH) human listeners of three age groups, investigating neural envelope encoding. HI young and middle-aged adults showed enhanced neural synchronization to envelope modulations relative to NH controls, particularly when stimulus audibility was corrected for. At an older age, the degree of neural synchronization was similar for HI and NH persons, yet HI persons showed a synchronization asymmetry toward the right hemisphere. This study demonstrates that hearing impairment is characterized by changes in the neural encoding of envelope modulations, the nature of which varies with age.

Neural envelope encoding predicts speech perception performance for normal-hearing and hearing-impaired adults

ABSTRACT Peripheral hearing impairment cannot fully account for speech perception difficulties that emerge with advancing age. As the fluctuating speech envelope bears crucial information for speech perception, changes in temporal envelope processing are thought to contribute to degraded speech perception. Previous research has demonstrated changes in neural encoding of envelope modulations throughout the adult lifespan, either due to age or due to hearing impairment. To date, however, it remains unclear whether such age‐ and hearing‐related neural changes are associated with impaired speech perception. In the present study, we investigated the potential relationship between perception of speech in different types of masking sounds and neural envelope encoding for a normal‐hearing and hearing‐impaired adult population including young (20–30 years), middle‐aged (50–60 years), and older (70–80 years) people. Our analyses show that enhanced neural envelope encoding in the cortex and in the brainstem, respectively, is related to worse speech perception for normal‐hearing and for hearing‐impaired adults. This neural‐behavioral correlation is found for the three age groups and appears to be independent of the type of masking noise, i.e., background noise or competing speech. These findings provide promising directions for future research aiming to develop advanced rehabilitation strategies for speech perception difficulties that emerge throughout adult life. HighlightsEnhanced neural envelope encoding is related to poorer speech perception.This association applies to speech masked by interfering noise or competing speech.Cortical envelope encoding predicts speech perception for normal‐hearing adults.Brainstem envelope encoding predicts speech perception for hearing‐impaired adults.Such neural‐behavioral relations are found for young, middle‐aged, and older adults.

How age affects memory task performance in clinically normal hearing persons.

ABSTRACT The main objective of this study is to investigate memory task performance in different age groups, irrespective of hearing status. Data are collected on a short-term memory task (WAIS-III Digit Span forward) and two working memory tasks (WAIS-III Digit Span backward and the Reading Span Test). The tasks are administered to young (20–30 years, n = 56), middle-aged (50–60 years, n = 47), and older participants (70–80 years, n = 16) with normal hearing thresholds. All participants have passed a cognitive screening task (Montreal Cognitive Assessment (MoCA)). Young participants perform significantly better than middle-aged participants, while middle-aged and older participants perform similarly on the three memory tasks. Our data show that older clinically normal hearing persons perform equally well on the memory tasks as middle-aged persons. However, even under optimal conditions of preserved sensory processing, changes in memory performance occur. Based on our data, these changes set in before middle age.