The pupil dilation response of adults with acquired brain injury during speech processing in noise

A significant group of adults with acquired brain injury (ABI) that have a normal pure tone audiogram, report difficulties and high levels of effort when listening to speech in noise. Listening difficulties in this group seem to be due to disturbed cognitive functioning when processing auditory information, independent of the peripheral hearing system. Notably, almost one third of people with ABI experience high levels of fatigue. According to the Framework for Understanding Effortful Listening (FUEL), fatigue may have a mediating effect on listening effort. To investigate this, we examined how ABI affects speech processing in noise and listening effort.

Twenty adults with ABI (aged 26-62 years) participated. All had a normal pure-tone audiogram (PTA) but reported difficulties with speech processing in noise. The participants listened to sentences masked by fluctuating noise or a single-talker at fixed intelligibility levels of 50% and 84% full sentence correct performance using a staircase procedure. The pupil diameter was recorded during each trial and used as an index of listening effort. Additionally, participants performed the Text Reception Threshold (TRT) task - a visual sentence completion task - measuring language related processing. Finally, data were compared to the results obtained for normally hearing and hearing impaired age-matched groups in earlier studies using the same design and setup.

A direct comparison between the current data and data recorded in a previous study including normal hearing participants with no neurological problems, revealed significant worse Speech Reception Thresholds for participants with ABI, which confirmed their reported hearing difficulties. This, while PTA as well as the performance on the TRT task was the same for both groups. While the same pattern of results for the pupil dilation response was shown over groups, self-rated effort scores were significantly higher for the ABI group compared to the normal hearing and hearing impaired groups.

Based on the outcomes of this study, we conclude that ABI and related fatigue affected speech perception most probably at a central auditory processing stage, which seemed to impact the participants listening effort.