Discrimination of spectral-peak amplitude by normal and hearing-impaired subjects

The present study compared the abilities of normal and hearing-impaired subjects to discriminate differences in the spectral shapes of speechlike sounds. The minimum detectable change in amplitude of a second-formant spectral peak was determined for steady-state stimuli across a range of presentation levels. In many cases, the hearing-impaired subjects required larger spectral peaks than did the normal-hearing subjects. The performance of all subjects showed a dependence upon presentation level. For some hearing-impaired subjects, high presentation levels resulted in discrimination values similar to that of normal-hearing subjects, while for other hearing-loss subjects, increases in presentation level did not yield normal values, even when the second-formant spectral region was presented at levels above the subject's sensitivity thresholds. These results demonstrate that under certain conditions, some sensorineural hearing-impaired subjects require more prominent spectral peaks in certain speech sounds than normal subjects for equivalent performance. For the group of subjects who did not achieve normal discrimination results at any presentation level, application of high-frequency amplification to the stimuli was successful in returning those subjects' performance to within normal values.