Non-linear frequency compression (NLFC) hearing aids aim to deliver high-frequency sound to a better functioning, lower frequency region of the cochlea. Despite the widespread use of frequency lowering technology, it continues to be difficult to predict candidacy. Since the aim of NLFC is to improve high-frequency audibility, possible predictors of benefit may include high-frequency hearing thresholds. NLFC alters the harmonic relationship of speech, and it has frequently been proposed that auditory training may help users adapt to the distorted acoustic signal. The aim of this thesis was twofold: firstly, to identify audiometric predictors of benefit from NLFC, and secondly to explore the role of auditory training in adaptation to NLFC. The first study aimed to determine if outcome with NLFC was related to hearing thresholds. Twenty-one experienced adult hearing aid users, with mild-to-profound high-frequency hearing loss, completed speech recognition and self-report measures with NLFC enabled and disabled over 16 weeks. The additional benefit gained on phoneme detection and word recognition tasks with NLFC enabled was positively correlated with average high-frequency hearing loss. Additional benefit began to emerge as average high-frequency hearing thresholds exceeded 70 dB HL. There was some evidence of a ‘roll-off’ in additional benefit when hearing thresholds exceeded 100 dB HL. The second study aimed to identify which training method, if any, may help adaptation to NLFC. Forty young normally hearing adults were randomly allocated to one of four groups: a training group (sentence or consonant) or a control group (passive exposure or test-only). Training led to significant improvements on novel measures of speech recognition. Generalisation was limited to near transfer i.e. sentence training led to improved sentence recognition whilst consonant training led to improved consonant recognition. Improvements following passive exposure to frequency compressed sentences were equivalent to those achieved by active sentence training. Results from this second study suggest that auditory training may improve outcome for users of NLFC hearing aids, but passive exposure may be an important confounding variable. In the final study high-frequency focused sentence and consonant training was compared to sham training (passive exposure to a talking book). Twenty-six hearing-impaired adults who were new users of NLFC were allocated to either an auditory training or a sham training group. Measures of speech recognition and self-report benefit were administered before and after four weeks of home-based training. Auditory training significantly improved speech reception thresholds. In conclusion, benefit from NLFC was dependent on hearing thresholds; as hearing thresholds increased so did benefit. Participants with severe-to-profound high-frequency hearing loss gained most benefit from NLFC. Auditory training provided alongside NLFC significantly improved speech recognition in noise but changes to all other outcome measures were not significant.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:689581 |
| Date | January 2016 |
| Creators | Dickinson, Ann-Marie |
| Contributors | Baker, Richard ; Munro, Kevin |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/nonlinear-frequency-compression-audiometric-predictors-of-benefit-and-the-role-of-auditory-training(de2f3330-2a7f-41c8-a835-c35e5c30c4c7).html |
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