Acoustically Transparent Hearing Aids Increase Physiological Markers of Listening Effort

While hearing aids are beneficial in compensating for hearing loss and suppressing ambient noise, they may also introduce an unwanted processing burden to the listener's sensory and cognitive system. To investigate such adverse side effects, hearing aids may be set to a 'transparent mode', aiming to replicate natural hearing through the open ear as best as possible. Such transparent hearing aids have previously been demonstrated to exhibit a small but significant disadvantage in speech intelligibility, with less conclusive effects on self-rated listening effort. Here we aimed to reproduce these findings and expand them with neurophysiological measures of invested listening effort, including parietal alpha power and pupil size. Invested listening effort was measured across five task difficulties, ranging from nearly impossible to easy, with normal-hearing participants in both aided and unaided conditions. Results well reproduced a hearing aid disadvantage for speech intelligibility and subjective listening effort ratings. As to be expected, pupil size and parietal alpha power followed an inverted u-shape, peaking at moderate task difficulties (around SRT50). However, the transparent hearing aid increased pupil size and parietal alpha power at medium task demand (between SRT20 and SRT80). These neurophysiological effects were larger than those observed in speech intelligibility and subjective listening effort, respectively. The results gain plausibility by yielding a substantial association of individual pupil size and individual parietal alpha power. In sum, our findings suggest that key neurophysiological measures of invested listening effort are sensitive to the individual additional burden on speech intelligibility that hearing aid processing can introduce.