Timbre discrimination in normal-hearing and hearing-impaired listeners under different noise conditions

In an attempt to quantify differences in object separation and timbre discrimination between normal-hearing and hearing-impaired listeners with a moderate sensorineural hearing loss of two different configurations, psychoacoustic measurements were performed with a total of 50 listeners. The experiments determined just noticeable differences (JND) of timbre in normal-hearing and hearing-impaired subjects along continua of "morphed" musical instruments and investigated the variance of JND in silence and different background noise conditions and on different sound levels. The results show that timbre JNDs of subjects with a steep hearing loss are significantly higher than of normal-hearing subjects, both in silence and noise, whereas timbre JNDs of flat/diagonal hearing-impaired subjects are similar to JNDs of normal-hearing subjects for signal levels above 55 dB (plus appropriate amplification for hearing-impaired). In noise (SNR=+10 dB) timbre JNDs of all subject groups are significantly higher than in silence. In the condition testing, transferability from silence to noise (i.e., the ability to imagine how the stimulus heard in silence would sound in noise), no significant JND differences across listener groups were found. The results can be explained by primary factors involved in sensorineural hearing loss and contradict the hypothesis that hearing-impaired people generally have more problems in object discrimination than normal-hearing people.