Zenke, Katharina; (2021) Spatial release from masking in children with and without auditory processing disorder in real and virtual auditory environments. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Auditory Processing Disorder (APD) is a developmental disorder characterised by difficulties in listening to speech-in-noise despite normal audiometric thresholds. It is still poorly understood and much disputed and there is a need for better diagnostic tools. One promising finding is that some children referred for APD assessment have a reduced spatial release from masking (SRM). Current clinical tests measure SRM in virtual auditory environments created from head-related transfer functions (HRTFs) of a standardised adult head. Adults and children, however, have different head dimensions and mismatched HRTFs are known to affect aspects of binaural hearing like localisation. There has been little research on HRTFs in children and it is unclear whether a large mismatch can impact speech perception, especially for children with APD who have difficulties with accurately processing auditory information. In this project, we examined the effect of nonindividualised virtual auditory environments on the SRM in adults and children with and without APD. The first study with normal-hearing adults compared environments created from individually measured HRTFs and two nonindividualised sets of HRTFs to a real anechoic environment. Speech reception thresholds (SRTs) were measured for target sentences at 0° and two symmetric speech maskers at 0° or ±90° azimuth. No significant effect of auditory environment on SRTs and SRM could be observed. A larger study was then conducted with APD and typically-developing children aged 7 to 12 years. Individual HRTFs were measured for each child. The SRM was measured in environments created from these individualised HRTFs or artificial head HRTFs and in the real anechoic environment. To assess the influence of spectral cues, SRTs were also measured for HRTFs from a spherical head model that only contains interaural time and level differences. Additionally, the study included an extended high-frequency audiogram, a receptive language test and two parental questionnaires. The SRTs of children with APD were worse than those of typically-developing children in all conditions but SRMs were similar. Only small differences in SRTs were found across environments, mainly for the spherical head HRTFs. SRTs in children were higher than in adults but improved with age. APD children also had higher hearing thresholds and performed worse in the language test.

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