Frequency discrimination of complex tones by hearing-impaired subjects: Evidence for loss of ability to use temporal fine structure.

For normally hearing subjects, thresholds for discriminating the fundamental frequency (F0) of a complex tone, F0DLs, increase when the number of the lowest harmonic, N, is above eight. A previous study showed that F0DLs were affected by component phase for N above 7, and it was argued that the increase in F0DLs with increasing N reflects a loss of temporal fine structure information. Here, subjects with moderate hearing loss were tested in a similar experiment. F0DLs were measured for tones with three successive harmonics, added in cosine or alternating phase. The center frequency was 2000 Hz. N was varied by changing the mean F0. A background noise was used to mask combination tones. F0 was roved across trials and N was roved by +/-1, to reduce use of excitation pattern cues. F0DLs were smaller for cosine than for alternating phase for four out of six subjects, and this occurred once N exceeded 5. In contrast to the result for normally hearing subjects, F0DLs decreased with increasing N. Performance was much worse than obtained for normally hearing subjects at the same center frequency, suggesting that most of the hearing-impaired subjects had a poor ability to use temporal fine structure information.