Limited information is known about the localisation skills of paediatric cochlear implant patients who were good hearing aid users before their hearing deteriorated. As localisation is a skill often associated with good natural hearing, there is a worry that implants will not be able to pick up the cues needed despite improving speech perception. The team in the Yorkshire Auditory Implant Service measured the sound source localisation accuracy (SLA) of 10 children with their bilateral hearing aids pre-cochlear implant (CI) compared with their one-year post-bilateral CI scores. Root mean square errors (RMS) and percentage correct scores showed improvements within subjects.
It is positive that the children not only generally developed better localisation abilities, but they did so within a year of implant use. There was no correlation between SLA scores and hearing threshold level overall or at low or high frequencies.
It may be that these patients had too poor hearing to be useful in localisation. However, the lowest frequencies, 125 and 250Hz, were not included in the assessment which could also have an effect on the results. Interestingly there was a tendency for CI users to localise better at 0 degree azimuth compared to when using hearing aids. This raises the point of microphone directionality impacting on the scores of these patients leading to better localisation in front. Implant companies are leaning towards directionality and roving microphones to help with speech in noise, but omnidirectional microphones may be better for localisation. Unfortunately microphone directionality is not looked at in this paper but it would be an interesting point to explore.