Edward C. Killan

Changes in children's speech discrimination and spatial release from masking between 2 and 4 years after sequential cochlear implantation.

Abstract Objective: To document changes in speech reception thresholds (SRTs) and spatial release from masking (SRM) for sequentially implanted children at 2 and 4 years after they received their second cochlear implant (CI2). Methods: Participants were 17 children who consistently used two sequentially implanted and optimally programmed CIs. SRTs were measured monaurally in quiet and binaurally in noise using the adaptive McCormick toy discrimination test. Speech signals were presented from 0° azimuth and noise from 0°, +90° or −90° azimuth. SRM was calculated from SRTs in noise. Measurements were made at 2 and 4 year post-CI2. Results: There were significant improvements over time in SRTs in quiet, SRTs in noise and SRM. SRTs in quiet improved more for CI2 than for the first implant (CI1). SRTs in noise and SRM improved more when noise was presented closest to CI1 than when closest to CI2. Performance became more symmetrical over time. Discussion: Despite prolonged periods of unilateral auditory deprivation sequentially implanted children exhibited continued improvement in SRT and SRM. These results are valuable in setting expectations for and counselling families of children considering sequential CIs.

CLINICALLY RELEVANT LONG-TERM RELIABILITY OF CONTRALATERAL SUPPRESSION OF CLICK-EVOKED OTOACOUSTIC EMISSIONS

Background: Contralateral suppression of click-evoked otoacoustic emissions (CEOAEs) are a potentially useful clinical tool. Recent studies have provided descriptions of the reliability of contralateral suppression of CEOAEs. These were limited in terms of their clinical relevance as they utilised custom-built measurement systems or were conducted by a single tester over a short time period. Further, in the main previous studies reported only group data. The present study addresses these limitations by reporting individual and group data collected by two testers, using standard clinical equipment over longer time periods. Materials and methods: Contralateral suppression of CEOAEs was recorded from 12 ears using the ILO 292 system. Clicks and contralateral broadband noise (BBN) were presented at 60 dB p.e. SPL and 65 dB SPL respectively. Global and best ½-octave band suppression values (in dB) were measured on four separate occasions by two testers spanning an average time period of 35.5 days. Reliability was assessed via the intraclass correlation coefficient (ICC) and the standard error of measurement (SEm). Multilevel regression analysis was used to explore potential causes of variation in suppression. Results: Global suppression reliability was shown to be worse than previous reports, with only fair to good reliability observed. ICC and SEm values were 0.57 and 0.47 dB respectively. Corresponding values for best ½-octave band suppression were 0.49 and 0.64 dB. Further analysis revealed no significant effect on contralateral suppression for a range of variables tested. Substantial variation (up to 2 dB) in contralateral suppression between test sessions was seen for individual subjects. Conclusions: Findings suggest that contralateral suppression of CEOAEs, measured by separate testers using standard clinical equipment is not reliable over long time periods.

Changes in sound-source localization for children with bilateral severe to profound hearing loss following simultaneous bilateral cochlear implantation

Background: Sound localization is a valuable skill that children can develop to some extent via bilateral cochlear implants (biCIs). However, little is known regarding the change that can be expected in sound-source localization accuracy (SLA) pre- and post-biCI for children with bilateral, severe-to-profound hearing impairment who spent their early years listening via bilateral hearing aids (biHAs). This study therefore aimed to prospectively assess SLA in a group of children before, and at one year after, receiving simultaneous biCIs. Methods: Ten children aged 5–18 years were tested. SLA was assessed using loudspeakers positioned at −60, −30, 0, +30, and +60 degrees azimuth. Root mean square (RMS) errors and percentage correct scores were calculated. Changes in SLA were analysed via paired t-tests and potential relationships between hearing threshold levels (HTLs) and SLA via correlation analyses. Response distributions via biHAs and biCIs were examined via scatterplots. Results: The mean within-subject changes in SLA were a significant improvement in RMS error of 11.9° (p < 0.05) and in per cent correct by 21.5% (p < 0.05). Scatterplots demonstrated a trend towards better localization of sounds from 0° azimuth via biCIs compared to via biHAs. No significant associations were found between any measures of SLA and HTLs. Conclusions: The findings of the present study demonstrate that simultaneous biCIs lead to improved sound localization in children with bilateral, severe to profound sensorineural hearing loss who previously used biHAs. SLA via biHAs or biCIs could not be predicted from children’s audiograms, and therefore should be measured directly.