Spatial release from masking in children with auditory processing disorder in virtual and real environments

Auditory Processing Disorder (APD) is a developmental disorder characterized by difficulties in listening to speech in noise despite normal audiometric thresholds. It is still poorly understood and much disputed and there is need for better diagnostic and intervention tools for young children, not least because of suspicions that APD leads to learning difficulties in language and literacy, and hence to poor school performance.

One promising avenue of research is the claim that around 20% of children referred for APD assessment are found to have a reduced spatial release from masking (SRM). Current clinical tests measure the SRM in virtual auditory environments generated with head-related transfer functions (HRTFs) from a standardized adult head. Adults and children, however, can be very different in head dimensions and mismatched HRTFs are known to affect localization accuracy. HRTFs in children have not been systematically measured so far and it is unclear whether HRTF mismatch also impacts speech perception, especially for children with APD due to their problems with processing auditory information.

In our current study, we measured individual HRTFs in children with diagnosed APD and typically-developing children aged 7 to 12 years. The SRM was measured for target sentences and two symmetric speech maskers in virtual auditory environments generated from these individualized HRTFs or HRTFs of an artificial adult head as well as in a real anechoic environment. In order to assess the influence of spectral pinna cues, we also measured speech reception thresholds for HRTFs gained from a spherical head model that only contains interaural time and level differences. Preliminary findings suggest differences in speech reception thresholds between listening conditions and slightly better overall performance of typically-developing children but similar amounts of SRM for all conditions. Both groups of children obtained significantly worse speech reception thresholds and smaller SRM as normal-hearing adults in our previous study.

We hope our results will help to determine the relevance of individualized spatial cues for SRM and further clarify the nature of spatial processing difficulties in children with APD.