Neural Alpha Dynamics in Younger and Older Listeners Reflect Acoustic Challenges and Predictive Benefits

Abstract

Speech comprehension in multitalker situations is a notorious real-life challenge, particularly for older listeners. Younger listeners exploit stimulus-inherent acoustic detail, but are they also actively predicting upcoming information? And further, how do older listeners deal with acoustic and predictive information? To understand the neural dynamics of listening difficulties and according listening strategies, we contrasted neural responses in the alpha-band (ϳ10 Hz) in younger (20 -30 years, n ϭ 18) and healthy older (60 -70 years, n ϭ 20) participants under changing task demands in a two-talker paradigm. Electroencephalograms were recorded while humans listened to two spoken digits against a distracting talker and decided whether the second digit was smaller or larger. Acoustic detail (temporal fine structure) and predictiveness (the degree to which the first digit predicted the second) varied orthogonally. Alpha power at widespread scalp sites decreased with increasing acoustic detail (during target digit presentation) but also with increasing predictiveness (in-between target digits). For older compared with younger listeners, acoustic detail had a stronger impact on task performance and alpha power modulation. This suggests that alpha dynamics plays an important role in the changes in listening behavior that occur with age. Last, alpha power variations resulting from stimulus manipulations (of acoustic detail and predictiveness) as well as task-independent overall alpha power were related to subjective listening effort. The present data show that alpha dynamics is a promising neural marker of individual difficulties as well as age-related changes in sensation, perception, and comprehension in complex communication situations.

Spatiotemporal dynamics of auditory attention synchronize with speech

“…The spatial cue at the beginning of each trial was a 1,000-Hz pure tone of 500-ms duration (50-ms linear onset ramp) equal in intensity to the spoken digits. Recordings of German digits ranged between 21 and 99 (excluding integer multiples of 10; sampling rate: 44.1 kHz) and were adopted from previous studies (6,49). Digits contained four syllables and had an average duration of 1.125 s. Root mean square intensity was equalized across digits.…”

“…The power of alpha oscillations (8)(9)(10)(11)(12) is modulated by the degree of selective attention to a behaviorally relevant stimulus (4)(5)(6). Attentive focusing to one side in auditory, visual, or tactile space leads to a relative decrease in alpha power in contralateral compared with ipsilateral sensory brain regions (7)(8)(9)(10) and governs success of selective attention, that is, of isolating one stimulus at a specific spatial location (11)(12)(13) in the context of other distracting stimuli.…”

Neural and Cognitive Effects of Hearing Loss on Speech Processing

“…Studies investigating the effect of temporal-fine structure on the alpha power report reduced inhibitory activity when listening to less degraded speech in younger (Obleser and Weisz, 2012;Becker et al, 2013) and older listeners (Wöstmann et al, 2015). Importantly, reducing the spectro-temporal information result in an alpha-power change during processing of intelligible speech, but not when processing unintelligible (spectrally rotated) speech (Becker et al, 2013).…”

“…That is, during a difficult listening task, the functional inhibition theory predicts an increase in alpha power because of the increased WM involvement, or cognitive load. Indeed, increased alpha power during auditory processing has been observed when (1) increasing the memory load (Leiberg et al, 2006;Kaiser et al, 2007;van Dijk et al, 2010;, (2) reducing the spectro-temporal detail (temporal-fine structure) of the stimuli (Obleser and Weisz, 2012;Becker et al, 2013;Wöstmann et al, 2015), (3) increasing the complexity of the speech material (Meyer et al, 2013), and when reducing the (4) temporal (Wilsch et al, 2014) and (5) contextual (Wöstmann et al, 2015) predictability of the stimuli. In all of the studies mentioned above (with the exception of Wilsch (2014)), alpha power increased over the parietal-occipital regions usually associated with processing of visual information.…”

“…Studies have observed a larger benefit of improving the speech quality (reducing the degradation) in older listeners, compared to younger, both in the alpha power (Wöstmann et al, 2015) and neural speech tracking (Presacco et al, 2016). As age and hearing acuity are often related, this suggests that care should be taken to ensure that any observed effects are indeed caused by worse hearing and not by increased age.…”