Abstract
OBJECTIVES: This study describes a vocoder-based frequency-lowering system that enhances spectral cues for nonsonorant consonants differing in place of articulation. The goal of this study was to evaluate the efficacy of this system for speech recognition by hearing-impaired listeners. DESIGN: Experiment 1 evaluated fricative consonant recognition in quiet. Eight fricatives in /VCV/ context were used. Experiment 2 evaluated consonant recognition in quiet with 22 consonants. Six listeners with steeply sloping high-frequency sensorineural hearing loss participated in experiment 1. The same six listeners and three additional listeners with flat/mid-frequency sensorineural hearing loss participated in experiment 2. Two processing conditions-frequency lowering and conventional amplification-were tested in each experiment. Insertion gains based on the NAL-RP formula were provided up to 8000 Hz for each processing condition. In addition, speech stimuli were low-pass (LP) filtered at 1000, 1500, and 2000 Hz to evaluate the effect of lack of high-frequency speech information on consonant perception with and without frequency lowering. For these LP speech conditions, amplification was provided up to the cutoff frequencies. Overall percent correct and percent information transmission were calculated for each processing and speech condition. RESULTS: The frequency-lowering system provided significant benefit for the perception of fricative consonants and perception of the place-of-articulation feature for hearing-impaired listeners without affecting their perception of sonorant consonants and other consonant features (i.e., voicing and nasality). The improvement of fricative consonant perception was observed for both wideband and LP speech conditions for the steeply sloping hearing-loss listeners. CONCLUSIONS: The results indicate that individuals with unaidable hearing loss above 1000 to 2000 Hz would receive significant benefit with the system compared with conventional amplification for the perception of fricative consonants, and more importantly, significant benefit for the perception of place of articulation.