Are you surprised to hear this? Longitudinal spectral speech exposure in older compared to middle-aged normal hearing adults.

Cognitive abilities such as attention or working memory can support older adults during speech perception. However, cognitive abilities as well as speech perception decline with age, leading to the expenditure of effort during speech processing. This longitudinal study therefore investigated age-related differences in electrophysiological processes during speech discrimination and assessed the extent of enhancement to such cognitive auditory processes through repeated auditory exposure. For that purpose, accuracy and reaction time were compared between 13 older adults (62-76 years) and 15 middle-aged (28-52 years) controls in an active oddball paradigm which was administered at three consecutive measurement time points at an interval of 2 wk, while EEG was recorded. As a standard stimulus, the nonsense syllable /'a:ʃa/was used, while the nonsense syllable /'a:sa/ and a morphing between /'a:ʃa/ and /'a:sa/ served as deviants. N2b and P3b ERP responses were evaluated as a function of age, deviant, and measurement time point using a data-driven topographical microstate analysis. From middle age to old age, age-related decline in attentive perception (as reflected in the N2b-related microstates) and in memory updating and attentional processes (as reflected in the P3b-related microstates) was found, as indicated by both lower neural responses and later onsets of the respective cortical networks, and in age-related changes in frontal activation during attentional stimulus processing. Importantly, N2b- and P3b-related microstates changed as a function of repeated stimulus exposure in both groups. This research therefore suggests that experience with auditory stimuli can support auditory neurocognitive processes in normal hearing adults into advanced age.

The impact of hearing aids and age-related hearing loss on auditory plasticity across three months - An electrical neuroimaging study.

The present study investigates behavioral and electrophysiological auditory and cognitive-related plasticity in three groups of healthy older adults (60-77 years). Group 1 was moderately hearing-impaired, experienced hearing aid users, and fitted with new hearing aids using non-linear frequency compression (NLFC on); Group 2, also moderately hearing-impaired, used the same type of hearing aids but NLFC was switched off during the entire period of study duration (NLFC off); Group 3 represented individuals with age-appropriate hearing (NHO) as controls, who were not different in IQ, gender, or age from Group 1 and 2. At five measurement time points (M1-M5) across three months, a series of active oddball tasks were administered while EEG was recorded. The stimuli comprised syllables consisting of naturally high-pitched fricatives (/sh/, /s/, and /f/), which are hard to distinguish for individuals with presbycusis. By applying a data-driven microstate approach to obtain global field power (GFP) as a measure of processing effort, the modulations of perceptual (P50, N1, P2) and cognitive-related (N2b, P3b) auditory evoked potentials were calculated and subsequently related to behavioral changes (accuracy and reaction time) across time. All groups improved their performance across time, but NHO showed consistently higher accuracy and faster reaction times than the hearing-impaired groups, especially under difficult conditions. Electrophysiological results complemented this finding by demonstrating longer latencies in the P50 and the N1 peak in hearing aid users. Furthermore, the GFP of cognitive-related evoked potentials decreased from M1 to M2 in the NHO group, while a comparable decrease in the hearing-impaired group was only evident at M5. After twelve weeks of hearing aid use of eight hours each day, we found a significantly lower GFP in the P3b of the group with NLFC on as compared to the group with NLFC off. These findings suggest higher processing effort, as evidenced by higher GFP, in hearing-impaired individuals when compared to those with normal hearing, although the hearing-impaired show a decrease of processing effort after repeated stimulus exposure. In addition, our findings indicate that the acclimatization to a new hearing aid algorithm may take several weeks.

Longitudinal auditory learning facilitates auditory cognition as revealed by microstate analysis.

The current study investigates cognitive processes as reflected in late auditory-evoked potentials as a function of longitudinal auditory learning. A normal hearing adult sample (n=15) performed an active oddball task at three consecutive time points (TPs) arranged at two week intervals, and during which EEG was recorded. The stimuli comprised of syllables consisting of a natural fricative (/sh/,/s/,/f/) embedded between two /a/ sounds, as well as morphed transitions of the two syllables that served as deviants. Perceptual and cognitive modulations as reflected in the onset and the mean global field power (GFP) of N2b- and P3b-related microstates across four weeks were investigated. We found that the onset of P3b-like microstates, but not N2b-like microstates decreased across TPs, more strongly for difficult deviants leading to similar onsets for difficult and easy stimuli after repeated exposure. The mean GFP of all N2b-like and P3b-like microstates increased more in spectrally strong deviants compared to weak deviants, leading to a distinctive activation for each stimulus after learning. Our results indicate that longitudinal training of auditory-related cognitive mechanisms such as stimulus categorization, attention and memory updating processes are an indispensable part of successful auditory learning. This suggests that future studies should focus on the potential benefits of cognitive processes in auditory training.