We analyzed the lateralization of the cortical auditory-evoked potential recorded previously from aided hearing-impaired listeners as part of a study on noise-mitigating hearing aid technologies. Specifically, we asked whether the degree of leftward lateralization in the magnitudes and latencies of these components was reduced by noise and, conversely, enhanced/restored by hearing aid technology. We further explored if individual differences in lateralization could predict speech-in-noise abilities in listeners when tested in the aided mode.
The study followed a double-blind within-subjects design. Nineteen older adults (8 females; mean age = 73.6 years, range = 56 to 86 years) with moderate to severe hearing loss participated. The cortical auditory-evoked potential was measured over 400 presentations of a synthetic /da/ stimulus which was delivered binaurally in a simulated aided mode using shielded ear-insert transducers. Sequences of the /da/ syllable were presented from the front at 75 dB SPL-C with continuous speech-shaped noise presented from the back at signal-to-noise ratios of 0, 5, and 10 dB. Four hearing aid conditions were tested: (1) omnidirectional microphone (OM) with noise reduction (NR) disabled, (2) OM with NR enabled, (3) directional microphone (DM) with NR disabled, and (4) DM with NR enabled. Lateralization of the P1 component and N1P2 complex was quantified across electrodes spanning the mid-coronal plane. Subsequently, listener speech-in-noise performance was assessed using the Repeat-Recall Test at the same signal-to-noise ratios and hearing aid conditions used to measure cortical activity.
As expected, both the P1 component and the N1P2 complex were of greater magnitude in electrodes over the left compared to the right hemisphere. In addition, N1 and P2 peaks tended to occur earlier over the left hemisphere, although the effect was mediated by an interaction of signal-to-noise ratio and hearing aid technology. At a group level, degrees of lateralization for the P1 component and the N1P2 complex were enhanced in the DM relative to the OM mode. Moreover, linear mixed-effects models suggested that the degree of leftward lateralization in the N1P2 complex, but not the P1 component, accounted for a significant portion of variability in speech-in-noise performance that was not related to age, hearing loss, hearing aid processing, or signal-to-noise ratio.
A robust leftward lateralization of cortical potentials was observed in older listeners when tested in the aided mode. Moreover, the degree of lateralization was enhanced by hearing aid technologies that improve the signal-to-noise ratio for speech. Accounting for the effects of signal-to-noise ratio, hearing aid technology, semantic context, and audiometric thresholds, individual differences in left-lateralized speech-evoked cortical activity were found to predict listeners’ speech-in-noise abilities. Quantifying cortical auditory-evoked potential component lateralization may then be useful for profiling listeners’ likelihood of communication success following clinical amplification.