Monitoring Alpha Oscillations and Pupil Dilation across a Performance-Intensity Function

Abstract

Listening to degraded speech can be challenging and requires a continuous investment of cognitive resources, which is more challenging for those with hearing loss. However, while alpha power (8–12 Hz) and pupil dilation have been suggested as objective correlates of listening effort, it is not clear whether they assess the same cognitive processes involved, or other sensory and/or neurophysiological mechanisms that are associated with the task. Therefore, the aim of this study is to compare alpha power and pupil dilation during a sentence recognition task in 15 randomized levels of noise (-7 to +7 dB SNR) using highly intelligible (16 channel vocoded) and moderately intelligible (6 channel vocoded) speech. Twenty young normal-hearing adults participated in the study, however, due to extraneous noise, data from only 16 (10 females, 6 males; aged 19–28 years) was used in the Electroencephalography (EEG) analysis and 10 in the pupil analysis. Behavioral testing of perceived effort and speech performance was assessed at 3 fixed SNRs per participant and was comparable to sentence recognition performance assessed in the physiological test session for both 16- and 6-channel vocoded sentences. Results showed a significant interaction between channel vocoding for both the alpha power and the pupil size changes. While both measures significantly decreased with more positive SNRs for the 16-channel vocoding, this was not observed with the 6-channel vocoding. The results of this study suggest that these measures may encode different processes involved in speech perception, which show similar trends for highly intelligible speech, but diverge for more spectrally degraded speech. The results to date suggest that these objective correlates of listening effort, and the cognitive processes involved in listening effort, are not yet sufficiently well understood to be used within a clinical setting.

Degradation levels of continuous speech affect neural speech tracking and alpha power differently

“…This is a region that has been reported to play a crucial role in complex speech comprehension (Van Ettinger-Veenstra et al 2016), especially important in successful comprehension of degraded but predictable speech (Obleser et al 2007;Hartwigsen et al 2015) and importantly in perceptual learning of degraded speech (Eisner et al 2010). The pattern of decreasing alpha power is further consistent with other studies using degradation of complex speech material as for example sentences (McMahon et al 2016;Miles et al 2017). However, studies using short and simple speech stimuli such as single words (Obleser and Weisz 2012;Becker et al 2013) or digits Wöstmann et al 2015) report enhanced alpha for stimuli with more acoustic detail compared to degraded sounds.…”

“…Another commonly used measure in studies of degraded speech -a common operationalization for listening effort-is the alpha rhythm (Obleser and Weisz 2012;McMahon et al 2016;Miles et al 2017). Interestingly, we found that alpha power followed a different pattern than coherence which became most obvious in study 2.…”

“…This modulation occurs when short degraded stimuli are used (Obleser and Weisz 2012;. However, in the rare -albeit more naturalistic-situation where sentences have been used, alpha power seems to show the opposite pattern (McMahon et al 2016;Miles et al 2017).…”

Consistent pre-stimulus influences on auditory perception across the lifespan

“…The lateralization of alpha power is indicative of visual-spatial attention (Thut et al, 2012;Wöstmann et al, 2016) and alpha band activity supposedly reflects the selection of sensory information by inhibition (Jensen and Mazaheri, 2010), for example via modulating the excitability of sensory cortices Kayser et al, 2015;Strauss et al, 2015). In auditory perception, the enhancement of alpha activity is often inversely related to signal intelligibility (Becker et al, 2013;McMahon et al, 2016;Obleser and Weisz, 2012;Scharinger et al, 2014;Wostmann et al, 2015), possibly reflecting age-related changes in attentional selection (Gazzaley et al, 2005;Henry et al, 2017;Wostmann et al, 2015). Therefore, it may not be surprising that the relation between alpha activity and perceptual decision making differed between groups.…”

Physiological methods as indexes of listening effort measurement: an integrative literature review

“…In addition, it is evident that studies in this area are relatively recent, since of the 18 selected articles, 72.2% [16][17][18][19][20][21][22][23][24][25][26][27][28] are from the last five years. It should also be noted that the analysis of the articles revealed the lack of national studies that measured the listening effort using physiological indexes as a method of measuring this parameter in both normal hearing individuals and hearing-impaired individuals.…”