The perception of telephone-processed speech by combined electric and acoustic stimulation

This study assesses the effects of adding low- or high-frequency information to the band-limited telephone-processed speech on bimodal listeners' telephone speech perception in quiet environments. In the proposed experiments, bimodal users were presented under quiet listening conditions with wideband speech (WB), bandpass-filtered telephone speech (300-3,400 Hz, BP), high-pass filtered speech (f > 300 Hz, HP, i.e., distorted frequency components above 3,400 Hz in telephone speech were restored), and low-pass filtered speech (f < 3,400 Hz, LP, i.e., distorted frequency components below 300 Hz in telephone speech were restored). Results indicated that in quiet environments, for all four types of stimuli, listening with both hearing aid (HA) and cochlear implant (CI) was significantly better than listening with CI alone. For both bimodal and CI-alone modes, there were no statistically significant differences between the LP and BP scores and between the WB and HP scores. However, the HP scores were significantly better than the BP scores. In quiet conditions, both CI alone and bimodal listening achieved the largest benefits when telephone speech was augmented with high rather than low-frequency information. These findings provide support for the design of algorithms that would extend higher frequency information, at least in quiet environments.