Electrode impedances in children with cochlear implants: Comparison between intra-operative Switch ON and post-operative Switch ON.

INTRODUCTION: Intra-operative Switch ON (IOSO) is a novel clinical approach of activating the cochlear implant during the surgery adopted at our cochlear implantation center.We compared the electrode impedances in two conditions of Switch ON of cochlear implants; IOSO and post-operative Switch ON (POSO, 21st day of surgery). METHODS: Electrode impedances of 185 cochlear implants, 93 of whom received IOSO and 92 POSO, recorded over 10 years were analyzed retrospectively. RESULTS: Electrode impedances of IOSO group were significantly lower than POSO group at Switch ON and 3rd, 6th, 9th, and 12th months post cochlear implantation. In IOSO group, 3rd month's electrode impedances were high when compared to electrode impedances at Switch ON. Beyond the 3rd months, electrode impedance remained unchanged. In POSO group, there were no significant differences in electrode impedances between any measurement schedule. CONCLUSIONS: To our knowledge, this is the first study to investigate in detail the electrode impedances of the two above-said conditions of Switch ON in the process of cochlear implantation. This study concludes that timing of CI Switch ON has a significant effect on the electrode impedances. These results may affect the choice of cochlear implant Switch ON timing.

Evaluation of Temporal Processing Abilities in Competing Noise.

Temporal processing is critical to a wide variety of everyday listening tasks, including speech perception. Although the importance of signal to noise ratio (SNR) is well documented in speech perception experiments, it is less explored in temporal processing experiments. The present study examined the effect of SNR on temporal processing abilities using Gap Detection Threshold (GDT) in children and adults. The study included a total of 45 subjects, where in, 25 children (Group-1) and 20 adults (Group-2) with pure-tone thresholds ranging from 0 to 25 dB HL at frequency range 250-8000 Hz. The GDT was measured at presentation level 50 dBSL. All the measurements were performed in 5 different conditions: 'Quiet', ' + 10 dB SNR', ' + 5 dB SNR', ' + 0 dB SNR' and ' - 5 dB SNR'. Gap Detection Thresholds are significantly higher from + 10 to - 5 dB SNR when compared to quiet condition in young-adults and all sub-groups of children, whereas at + 10 dB SNR, thresholds were not significantly different from quiet condition in young-adults and all sub-groups of children except for sub-group A of children, and were significantly different for all the five conditions. It was revealed that, as the signal to noise ratio (SNR) was decreased from + 10 dB SNR to 0 dB SNR there was a significant increase in Gap Detection Thresholds. There was a significant increase in Gap Detection Thresholds from + 10 dB SNR to - 5 dB SNR in both children and adults. The results also suggest that the performance on temporal processing task in the presence of background noise achieves young-adult like pattern by the age of 10-11 years. Background noise affect temporal processing in both children and young-adults. Background noise impairs temporal processing in children more than the adults, which could be because of poor temporal resolving abilities in children.

Acoustic Reflexes in Individuals Having Hyperacusis of the Auditory Origin.

Functional role of the acoustic reflex in preventing over stimulation of the inner auditory system by decreasing sound intensity along with the previous reports of acoustic reflex abnormalities in individuals having hyperacusis point towards the involvement of acoustic reflex deficit in the origin of hyperacusis especially when any medical condition leading to hyperacusis is not associated. However this issue remains contradictory owing to limited comprehensive investigation. This study was undertaken to ascertain the relationship between hyperacusis and the acoustic reflex. Threshold, amplitude and latency of the acoustic reflex were measured in two different groups of individuals having hyperacusis; Group 1: 14 individuals having hyperacusis with hearing loss (HwHL) and Group 2: 17 individuals having hyperacusis without hearing loss (HwoHL). Control group (Group 3) consisted of 15 normal hearing individuals who never experienced hyperacusis. Result showed a significant group effect on all the measured characteristics of the acoustic reflex. ARTs were found to be significantly higher in HwHL and HwoHL when compared to NHwoH. ARTs were statistically similar for HwoHL and NHwoH. HwoHL's ARAs and ARLs were significantly smaller and prolonged, respectively, when compared to HwHL and NHwoH. HwHL and NHwoH had statistically similar ARAs and ARLs. This study confirms acoustic reflex abnormalities in some individuals having hyperacusis with or without hearing loss. It further highlight the importance of involving acoustic reflex testing in the assessment of hyperacusis especially when hyperacusis is not associated with hearing loss or any other medical condition that may lead to hyperacusis.