Using transposition to improve consonant discrimination and detection for listeners with severe high-frequency hearing loss.

Transposition of high-frequency information to lower frequencies may help people with high-frequency hearing loss associated with a 'dead region' (DR) to detect and identify certain consonants, such as 's'. Conventional high-frequency amplification is often not beneficial in such cases. We designed and evaluated a new transposition algorithm which was adapted to each subject's high-frequency DR. Frequency components from well within the DR were transposed to just within the DR without applying frequency compression. Low-frequency components were amplified, but unaffected by transposition. Transposition only occurred if there was significant high-frequency energy, preventing high-frequency background noise of moderate level from being transposed. Consonant discrimination was tested using vowel-consonant-vowel (VCV) stimuli, and the detection of word-final 's' and 'z' was assessed using word pairs. Seven subjects with high-frequency DRs were tested in quiet using a transposed and a control condition. Following transposition, two subjects improved significantly and none performed significantly worse on the VCV-test overall. The perception of affricates was consistently improved. Averaged across subjects, the detection of word-final 's' and 'z' was significantly improved, with five subjects improving significantly individually.