Stuart Rosen1, Tim Schoof1, Tim Green1
1UCL Speech, Hearing & Phonetic Sciences, London, U.K.
Much interest surrounds the possible contribution of synaptopathy and/or neuropathy (SNpathy) to hearing difficulties that occur despite normal audiometric thresholds. We made extensive measurements in two groups of listeners with near-normal audiograms who were expected to differ greatly in the likelihood of SNpathy: 19 Y(oung) adults aged 18-25 with limited noise exposure and 23 M(iddle-aged) adults aged 44-61 with significant noise exposure. Speech reception thresholds (SRTs) were measured binaurally in speech-spectrum-shaped noise for two tasks (recognition of complex sentences and consonant identification in VCVs). To assess the use of temporal fine structure (TFS), target and masker were presented either diotically (S0N0) or with the masker in phase at the two ears and the target out of phase (SπN0). Stimuli were presented at both a high and a low level (40 and 80 dB SPL) to assess claims that deficits due to SNpathy might be more prominent at high levels. Although the relationships among various predictors and the outcome were fairly complex, generally speaking: 1) The mean performance of the Y group was always better than that of the M group, with differences ranging from 0.3 to 3.5 dB across the 8 conditions. 2) SRTs worsened across age in the M group for some conditions, meaning that the younger M listeners could be performing similarly to the Y group. 3) Greater deficits were found for SπN0 than forS0N0 conditions, implicating some deficits in the M group for processing TFS. 4) The effect of level was small, especially when comparing the two groups. 5) Group differences in SRTs were not related to a small difference in audiometric thresholds at frequencies ≤ 4 kHz. It therefore seems possible that SNpathy could be a factor in these relatively small group differences, but that these effects differ little across level.
Acknowledgements: Funded by the RNID UK.