Unilateral acoustic degradation delays attentional separation of competing speech

Abstract

Hearing loss is often asymmetric, such that hearing thresholds differ substantially between the two ears. The extreme case of such asymmetric hearing is single-sided deafness. A unilateral cochlear implant (CI) on the more severely impaired ear is an effective treatment to restore hearing. The neuro-cognitive cost of listening with a unilateral CI in multi-talker situations is at present unclear. Here, we simulated listening with a unilateral CI in young, normal-hearing listeners (N = 22) who were presented with 8-band noise-vocoded speech to one ear and intact speech to the other ear. Neural responses were recorded in the electroencephalogram (EEG) to obtain the spectro-temporal response function (sTRF) to speech. Listeners made more mistakes when answering questions about vocoded (versus intact) attended speech, indicating the behavioural cost of attending to spectrally degraded speech. At the neural level, we asked how unilateral acoustic degradation would impact the attention-induced amplification of tracking target versus distracting speech. Interestingly, unilateral degradation did not per se reduce the attention-induced amplification but instead delayed in time: Speech encoding accuracy, modelled on the basis of the sTRF, was significantly enhanced for attended versus ignored intact speech at earlier neural response latencies (<~250 ms). Notably, this attentional enhancement was not absent but delayed for vocoded speech. These findings suggest that attentional selection of unilateral, degraded speech is feasible but comes at the cost of delayed neural separation of competing speech, which might explain listening challenges experienced by unilateral CI users.

Hearing loss is associated with delayed neural responses to continuous speech

“…In several studies, it has been shown that NH listeners show an increased neural response latency with increasing task demand due to lower stimulus intensity, increasing background noise or stimulus vocoding. This is the case for neural processing of continuous speech (Kraus et al, 2021; Mirkovic et al, 2019; Verschueren et al, 2021) as well as simple sounds (Billings et al, 2015; Maamor & Billings, 2017; McClannahan et al, 2019; Van Dun et al, 2016). In the current study, we observed the same effect for NH listeners: When speech understanding decreases, NH listeners showed a prominent increase in latency of the neural responses.…”

“…Hence, they might allocate more effort to listen the stimulus. Listening to degraded speech (e.g., Kraus et al, 2021; Mirkovic et al, 2019; Verschueren et al, 2021) or spending more effort to listen to the stimulus (e.g., Dimitrijevic et al, 2019) affects the neural responses to continuous speech. By providing amplification, we aimed to make the peripheral activation levels as similar as possible in both groups, which motivates our choice to model the neural responses to the non‐amplified speech features for HI listeners.…”

Speech understanding oppositely affects acoustic and linguistic neural tracking in a speech rate manipulation paradigm

“…The latency of the first peak increases with increasing speech rate. Increased latencies are often observed in more complex conditions with a higher task demand, like for example lower stimulus intensity, vocoded speech or speech in noise (Mirkovic et al, 2019; Verschueren et al, 2021; Kraus et al, 2020). The latency of the neural responses can also be related to neural processing efficiency (Bidelman et al, 2019; Gillis et al, 2021a).…”

Hearing loss is associated with delayed neural responses to continuous speech

“…In several studies, it has been shown that NH listeners show an increased neural response latency with increasing task demand due to lower stimulus intensity, increasing background noise or stimulus vocoding. This is the case for neural processing of continuous speech (Mirkovic et al, 2019; Verschueren et al, 2020; Kraus et al, 2020) as well as simple sounds (Billings et al, 2015; Van Dun et al, 2016; Maamor and Billings, 2017; McClannahan et al, 2019). Our results show that this increase in latency is absent for adults with a higher degree of hearing loss (Figure 5.C).…”

“…Listening to degraded speech (e.g. Mirkovic et al, 2019;Verschueren et al, 2021;Kraus et al, 2020) or spending more effort to listen to the stimulus (e.g. Dimitrijevic et al, 2019) affects the neural responses to continuous speech.…”