Shining a light on the neural signature of effortful listening

Abstract

This study used functional near-infrared spectroscopy (fNIRS) to investigate a possible neural correlate of effortful listening. Hearing-impaired individuals report more listening effort than their normally hearing peers, with negative consequences in daily life (e.g., increased absenteeism from work). Listening effort may reflect neuro-cognitive processing underlying the recovery of meaning from a degraded auditory signal. Indeed, evidence from functional magnetic resonance imaging (fMRI) suggests that the processing of degraded speech is associated with increased activation in cortical areas outside the main auditory regions within the temporal lobe. However, acoustic scanner noise presents a serious methodological challenge in fMRI. This challenge can potentially be overcome using fNIRS, a silent, non-invasive brain-imaging technique based on optical measurements. In the current study, we used fNIRS to confirm the finding that attentive listening to degraded (noise-vocoded) speech leads to increased activation in the left inferior frontal gyrus (LIFG), compared to a clear-speech control condition. In contrast, robust activation in the auditory cortices was unaffected by speech clarity or attentional focus. Our results support the suggestion that the LIFG plays a role in compensating for degradation to the speech signal. Furthermore, fNIRS may hold promise as a flexible tool to examine the neural processes underlying effortful listening.