Browsing by Author "Cowan, Robert"

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    Clinical Outcomes for Adult Cochlear Implant Recipients Experiencing Loss of Usable Acoustic Hearing in the Implanted Ear
    (Wolters Kluwer Health, Inc, 2015-05) Plant, Kerrie; van Hoesel, Richard; McDermott, Hugh; Dawson, Pamela; Cowan, Robert
    OBJECTIVES: The first aim of the study was to quantify the change in clinical performance after cochlear implantation for adults who had pre-operative levels of acoustic hearing in each ear of greater than or equal to 46% phoneme score on an open-set monosyllabic word test, and who subsequently experienced loss of useable acoustic hearing in the implanted ear. Pre- and postoperative spatial hearing abilities were assessed, because a clinical consideration for candidates with bilateral acoustic hearing is the potential for post-operative reduction in spatial hearing ability. Second, it was of interest to examine whether preoperative localization ability, as an indicator of access to interaural timing and level cues preoperatively, might be correlated with post-operative change in spatial hearing abilities. DESIGN: Clinical performance measures in the binaural condition were obtained preoperatively and at 12 months postoperatively in 19 postlinguistically hearing-impaired adult subjects. Preoperative localization ability was investigated as a potential correlate with post-operative change in spatial hearing abilities. RESULTS: Significant postoperative group mean improvement in speech perception was observed on measures of open-set monosyllabic word perception in quiet and on an adaptive sentence test presented in coincident 4-talker babble. Observed benefit was greater for a lower presentation level of 55 dB SPL as compared with a conversational speech level of 65 dB SPL. Self-reported ratings of benefit also improved for all questionnaires administered. Objective assessment of localization ability revealed poorer localization postoperatively, although subjective ratings of post-operative change in localization ability in real-world environments were more variable. Postoperative spatial release from masking was not different to that measured preoperatively for the configuration where the side of the head with the hearing aid was advantaged, but improved postoperatively for the configuration that advantaged the implanted side. Preoperative binaural localization ability was not correlated with postoperative spatial hearing abilities. CONCLUSIONS: The findings from this study support cochlear implantation for candidates with pre-operative levels of binaural acoustic hearing within the range examined within the present study. This includes subjects with preoperative open-set monosyllabic word scores ranging from 11 to 62% in the implanted ear, and from 16 to 75% on the contralateral side. Post-operative improvement would be expected for those subjects on a range of clinical measures, even when acoustic hearing was lost in the implanted ear after implantation.
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    Factors Predicting Postoperative Unilateral and Bilateral Speech Recognition in Adult Cochlear Implant Recipients with Acoustic Hearing
    (Wolters Kluwer Health, Inc., 2015-10) Plant, Kerrie; McDermott, Hugh; van Hoesel, Richard; Dawson, Pamela; Cowan, Robert
    OBJECTIVES: The first objective was to examine factors that could be predictive of postoperative unilateral (cochlear implant alone) speech recognition ability in a group of subjects with greater degrees of preoperative acoustic hearing than has been previously examined. Second, the study aimed to identify factors predictive of speech recognition in the best-aided, bilateral listening condition. DESIGN: Participants were 65 postlinguistically hearing-impaired adults with preoperative phoneme in quiet scores of greater than or equal to 46% in one or both ears. Preoperative demographic and audiometric factors were assessed as predictors of 12-month postoperative unilateral and bilateral monosyllabic word scores in quiet and of bilateral speech reception threshold (SRT) in babble. RESULTS: The predictive regression model accounted for 34.1% of the variance in unilateral word recognition scores in quiet. Factors that predicted better scores included: a shorter duration of severe to profound hearing loss in the implanted ear; and poorer pure-tone-averaged thresholds in the contralateral ear. Predictive regression models of postimplantation bilateral function accounted for 36.0% of the variance for word scores in quiet, and 30.9% of the variance for SRT in noise. A shorter duration of severe to profound hearing loss in the implanted ear, a lower age at the time of implantation, and better contralateral hearing thresholds were associated with higher bilateral word recognition in quiet and SRT in noise. CONCLUSIONS: In this group of cochlear implant recipients with preoperative acoustic hearing, a shorter duration of severe to profound hearing loss in the implanted ear was shown to be predictive of better unilateral and bilateral outcomes. However, further research is warranted to better understand the impact of that factor in a larger number of subjects with long-term hearing impairment of greater than 30 years. Better contralateral hearing was associated with poorer unilateral word scores with the implanted ear alone, but better absolute bilateral speech recognition. As a result, it is clear that different models would need to be developed to predict unilateral and bilateral postimplantation scores.
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    Impedance changes in chronically implanted and stimulated cochlear implant electrodes.
    (WS Maney & Son, 2014) Newbold, Carrie; Mergen, Silvana; Richardson, Rachael; Seligman, Peter; Millard, Rodney; Cowan, Robert; Shepherd, Robert
    OBJECTIVES: Electrode impedance increases following implantation and undergoes transitory reduction with onset of electrical stimulation. The studies in this paper measured the changes in access resistance and polarization impedance in vivo before and following electrical stimulation, and recorded the time course of these changes. DESIGN: Impedance measures recorded in (a) four cats following 6 months of cochlear implant use, and (b) three cochlear implant recipients with 1.5-5 years cochlear implant experience. RESULTS: Both the experimental and clinical data exhibited a reduction in electrode impedance, 20 and 5% respectively, within 15-30 minutes of stimulation onset. The majority of these changes occurred through reduction in polarization impedance. Cessation of stimulation was followed by an equivalent rise in impedance measures within 6-12 hours. CONCLUSIONS: Stimulus-induced reductions in impedance exhibit a rapid onset and are evident in both chronic in vivo models tested, even several years after implantation. Given the impedance changes were dominated by the polarization component, these findings suggest that the electrical stimulation altered the electrode surface rather than the bulk tissue and fluid in the cochlea.
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    Influence of contralateral acoustic hearing on adult bimodal outcomes after cochlear implantation
    (Taylor & Francis Online, 2016-08) Plant, Kerrie; van Hoesel, Richard; McDermott, Hugh; Cowan, Robert
    OBJECTIVE: To examine post-implantation benefit and time taken to acclimate to the cochlear implant for adult candidates with more hearing in the contralateral non-implanted ear than has been previously considered within local candidacy guidelines. DESIGN: Prospective, within-subject experimental design. STUDY SAMPLE: Forty postlingual hearing-impaired adult subjects with a contralateral ear word score in quiet ranging from 27% to 100% (median 67%). RESULTS: Post-implantation improvement of 2.4 dB and 4.0 dB was observed on a sentence in coincident babble test at presentation levels of 65 and 55 dB SPL respectively, and a 2.1 dB benefit in spatial release from masking (SRM) advantage observed when the noise location favoured the implanted side. Significant post-operative group mean change of between 2.1 and 3.0 was observed on the sub-scales of the speech, spatial, and qualities (SSQ) questionnaire. Degree of post-implantation speech reception threshold (SRT) benefit on the coincident babble test and on perception of soft speech and sounds in the environment was greater for subjects with less contralateral hearing. The degree of contralateral acoustic hearing did not affect time taken to acclimate to the device. CONCLUSIONS: The findings from this study support cochlear implantation for candidates with substantial acoustic hearing in the contralateral ear, and provide guidance regarding post-implantation expectations.
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    Speech Perception Outcomes for Adult Cochlear Implant Recipients Using a Lateral Wall or Perimodiolar Array
    (Wolters Kluwer Health, Inc, 2019-04) Moran, Michelle; Vandali, Andrew; Briggs, Robert; Dettman, Shani; Cowan, Robert; Dowell, Richard
    AIM: To assess the speech perception outcomes of adult CI recipients with significant preimplant low frequency hearing, examining differences between perimodiolar and lateral wall electrode placement in order to provide clinical guidance for clinicians and surgeons. METHODS: A prospective cohort study was undertaken identifying all adults who received a thin straight electrode array (TSEA) at the Royal Victorian Eye & Ear Hospital (RVEEH) from 2010 to 2015 and who had a preimplant low frequency pure tone median