Purpose: To evaluate how perceptual importance of spectral tilt is altered when formant information is degraded by sensorineural hearing loss.
Method: Eighteen listeners with mild to moderate hearing impairment (HI listeners) and 20-23 listeners with normal hearing (NH listeners) identified synthesized stimuli that varied in second formant (F(2)) frequency and spectral tilt. Experiments 1 and 2 examined utterance-initial stops (/ba/ and /da/), and Experiments 3 and 4 examined medial stops (/aba/ and /ada/). Spectral tilt was manipulated at either consonant onset (Experiments 1 and 3), vowels (Experiments 2 and 4), or both (Experiment 5).
Results: Regression analyses revealed that HI listeners weighted F(2) substantially less than NH listeners. There was no difference in absolute tilt weights between groups. However, HI listeners emphasized tilt as much as F(2) for medial stops. NH listeners weighted tilt primarily when F(2) was ambiguous, whereas HI listeners weighted tilt significantly more than NH listeners on unambiguous F(2) endpoints.
Conclusions: Attenuating changes in spectral tilt can be as deleterious as taking away F(2) information for HI listeners. Recordings through a wide dynamic range compression hearing aid show compromised changes in spectral tilt, compressed in range by up to 50%.