Effect of linear and warped spectral transposition on consonant identification by normal-hearing listeners with a simulated dead region.

We investigated the potential benefits for consonant identification of a form of frequency transposition intended for people with severe or profound hearing loss at high frequencies, but near-normal hearing at low frequencies. Frequency components from a 'source band' in a high-frequency region were transposed downwards to a 'destination band'. All experiments used normal-hearing listeners. Experiment 1 showed that (untransposed) source bands centred near 4 kHz yielded highest identification scores. Also, performance was better when the source band was wider. Experiment 2 used transposition with the 'best' source bands from experiment 1, and showed that superimposing the transposed components on the components in the destination band gave better results than replacing the latter by the former. Experiment 3 assessed the effects of focused training, using conditions without and with transposition. Significant improvements occurred with training, but overall performance following training was similar for all conditions. However, transposition reduced some frequent errors.