Florian Denk1, Florian Miethling1, Jürgen Tchorz2, Hendrik Husstedt1
Deutsches Hörgeräte Institut GmbH, Lübeck, Germany
2Technische Hochschule Lübeck, Germany

While hearing aids provide large benefits for hearing impaired users, it has been repeatedly shown that wearing hearing aids has also detrimental effects on sound localization, spatial hearing and speech perception. Such ‘side effects’ reduce the benefit of hearing aids, and may outweigh them in potential users with a mild or moderate hearing loss, or normal-hearing users of related devices like hearables. This also holds if the hearing aids are adjusted to a transparent setting, i.e., conserve the transmission behavior of the open ear as close as possible given technical limitations like the microphone location, processing delays or self-noise. To gain further insight into the mechanisms impairing speech intelligibility with hearing aids, we equipped normal-hearing subjects with behind-the-ear hearing aids in a transparent setting, and measured the speech intelligibility in different spatial listening situations with noise and speech maskers. These situations included collocated speech and masker, and speech spatially separated from four distributed masker sources, where the direction of the speech source was either static or randomly changed between sentences. The results show generally increased speech reception thresholds in the aided condition as compared to the open ear, a reduced spatial release from masking, and a decreased advantage of the speech masker with respect to the noise masker, particularly in the condition where the speech source direction was randomly varied. Based on an analysis of the KEMAR-recorded stimuli, we discuss which of these results can be attributed to a change in energetic masking effects and disturbed binaural cues, or whether wearing the hearing aids further impaired the segregation of speech and masker on a higher cognitive level.