Your eyes and brain reveal your hearing ability

A relevant aspect of listening is the degree of effort required to understand the message. We assessed the neural correlates of the pupil dilation response, a measure of listening effort, in two samples of individually age-matched and educational-level matched participants. One group (n=17) included listeners (M age 45.9 years) with normal hearing; the other group comprised listeners (n = 17; M age 45.4 years) with sensorineural hearing loss (mean PTA 46.9 dB HL). Participants repeated sentences that were degraded by noise-vocoding the speech, by imposing stationary noise, or by imposing interfering speech. Speech Reception Thresholds (SRTs) aiming at 50% intelligibility were adaptively estimated, pupil dilation responses were assessed and functional magnetic resonance imaging (fMRI) data were acquired.

As expected, hearing impairment was associated with relatively poor SRTs, especially for interfering speech. Brain activation and pupil dilation responses were largest for this condition. Effects of degradation type were observed in bilateral superior temporal and superior and middle frontal gyri, bilateral precentral gyrus, and left inferior frontal gyrus. Pupil dilation responses of the hearing impaired participants tended to be smaller and a frontal area tended to be less active than in the normal hearing controls. Activation in a variety of frontal, temporal and medial brain regions was associated with the pupil response. Part of these regions reflected condition-specific effects.

The results extend previous findings showing the effect of hearing acuity and speech degradation on speech perception and the pupil and brain responses during listening. We will discuss the relevant processes underlying the results.