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.
Highlights
Listening to degraded speech, either in adverse acoustic environments or with hearing loss, is challenging (McCoy et al, 2005; Stenfelt and Rönnberg, 2009), and it is assumed that the increased cognitive load required to understand a conversation is associated with self-reported effort (Lunner et al, 2009; Rudner et al, 2012)
For the 16-channel vocoding, for every unit increase in signal-to-noise ratios (SNRs), SRS increased by 6.44% for the fixed versus 6.47% for the randomized presentation, showing that the slopes by mode of presentation overlap considerably
The results of this study suggest that, while there was a significant and expected difference in speech recognition performance and effort rating between the 6- and 16-channel vocoded material across the 15 SNRs, the mean changes observed in the physiological measures were less predictable
Summary
Either in adverse acoustic environments or with hearing loss, is challenging (McCoy et al, 2005; Stenfelt and Rönnberg, 2009), and it is assumed that the increased cognitive load required to understand a conversation is associated with self-reported effort (Lunner et al, 2009; Rudner et al, 2012). Concurrently measuring the cognitive load or listening effort needed to undertake a speech perception task could increase its sensitivity, enabling a more holistic understanding of the challenges faced by adults with hearing loss in communicative settings. As hearing loss and cognitive decline are highly associated with age (Salthouse, 2004; Lin et al, 2013), there is a recognized need to understand the contribution of cognition and effort to listening to everyday speech within a clinical environment to better direct rehabilitation strategies towards and/or improve device fitting, for older adults. Several studies have highlighted the advantages that individuals with greater cognitive resources have to understand speech in noise (Lunner, 2003), utilize fast signal processing strategies in hearing aids (Lunner and Sundewall-Thorén, 2007), and compensate when mismatches occur between what is heard and the brain’s phonological representations of speech (Avivi-Reich et al, 2014)
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