The Role of Temporal Envelope and Fine Structure in Mandarin Lexical Tone Perception in Auditory Neuropathy Spectrum Disorder

Temporal information in a signal can be partitioned into temporal envelope (E) and fine structure (FS). Fine structure is important for lexical tone perception for normal-hearing (NH) listeners, and listeners with sensorineural hearing loss (SNHL) have an impaired ability to use FS in lexical tone perception due to the reduced frequency resolution. The present study was aimed to assess which of the acoustic aspects (E or FS) played a more important role in lexical tone perception in subjects with auditory neuropathy spectrum disorder (ANSD) and to determine whether it was the deficit in temporal resolution or frequency resolution that might lead to more detrimental effects on FS processing in pitch perception. Fifty-eight native Mandarin Chinese-speaking subjects (27 with ANSD, 16 with SNHL, and 15 with NH) were assessed for (1) their ability to recognize lexical tones using acoustic E or FS cues with the "auditory chimera" technique, (2) temporal resolution as measured with temporal gap detection (TGD) threshold, and (3) frequency resolution as measured with the Q(10dB) values of the psychophysical tuning curves. Overall, 26.5%, 60.2%, and 92.1% of lexical tone responses were consistent with FS cues for tone perception for listeners with ANSD, SNHL, and NH, respectively. The mean TGD threshold was significantly higher for listeners with ANSD (11.9 ms) than for SNHL (4.0 ms; p < 0.001) and NH (3.9 ms; p < 0.001) listeners, with no significant difference between SNHL and NH listeners. In contrast, the mean Q(10dB) for listeners with SNHL (1.8 ± 0.4) was significantly lower than that for ANSD (3.5 ± 1.0; p < 0.001) and NH (3.4 ± 0.9; p < 0.001) listeners, with no significant difference between ANSD and NH listeners. These results suggest that reduced temporal resolution, as opposed to reduced frequency selectivity, in ANSD subjects leads to greater degradation of FS processing for pitch perception.