Audiology and Speech Pathology - Theses
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ItemExploring the variance in cochlear implant outcomes as a function of information-processing ability( 2016)The modern cochlear implant (CI) is a medical prosthesis that restores to its hearing-impaired users the ability to hear speech. Most CI recipients are generally able to achieve a good level of speech understanding, but there remains substantial variability in overall speech perception outcomes that cannot be explained by demographic and audiologic factors alone. The purpose of this study was to explore top-down or cognitive processing ability as an additional source of variability in outcomes for postlingually-deafened adult CI users. Psychophysical measures of bottom-up processing ability were also used to assess the amount of useful speech information discriminable by CI recipients. Taken together, it was hypothesised that these measures would account for more of the overall variance in CI speech perception, adding to current knowledge about predictor variables that have traditionally been considered to be important for good auditory outcomes. Adult CI candidates were recruited prior to surgery from the Melbourne and Sydney Cochlear Implant Clinics (n=37) and assessed using a cognitive test battery. These tests were designed to assess domains related to working memory, processing speed, IQ, mental flexibility, and verbal learning. Bottom-up processing ability was assessed approximately three months after surgery using tests of gap detection threshold and electrode discrimination. Postoperative auditory outcomes were monosyllabic word perception scores at three months post-implantation in the monaural and binaural listening conditions. The findings from this study revealed that age at implantation was the most important factor in both listening conditions. In addition, information-processing speed, residual hearing in the contralateral ear, and binaural hearing aid use were also found to be significant factors for binaural speech perception outcomes. Together, the four factors in the binaural model accounted for approximately 48% of the variance in binaural word perception scores, while the monaural model accounted for approximately 16% of the variance in word perception scores using the CI alone. Gap detection threshold was also found to be significantly correlated with speech perception outcomes, indicating that temporal resolution ability is important for successful speech recognition using the CI. These findings have implications for future clinical practice, adding further knowledge to the evidence-based guidelines that inform clinical decision-making and CI candidacy criteria. Most importantly, the significant finding of age at implantation strongly suggests that CI recipients will have better outcomes if they are implanted earlier in the progression of their hearing loss.