The Use of the Phase Locking Information in the Human Auditory System for Frequencies Above 5 kHz |
| A. Sęk and M. Bukała
Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland |
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| Accurate allocation of neural impulses to the same phase (i.e. phase locking) in the auditory system, ceases for frequencies above 5 kHz. However, some recent works suggest that it may have a much higher value. A discrimination of harmonic complex and inharmonic complex sound, formed using sound harmonic complex, in which all components were shifted towards higher frequency by the same number in hertzs, was analyzed. Fundamental frequency was F0=1 kHz and signals were bandpass filtered by a fixed filter center frequency of which was 11F0 and bandwidth 5F0. Discrimination threshold was Δ F=0.089F0 for 10 normal-hearing subjects. However, replacing the sinusoidal components with the noise bands brought about a significant increase in thresholds. The largest increase was observed for 700 Hz bandwidth. The replacement of sinusoidal components with noisebands reduces information conveyed by phase locking. The differences in excitation pattern for harmonic complex and inharmonic complex signals, for the average threshold, did not exceed 0.7 dB. Therefore they could not be a useful cue for harmonic complex and inharmonic complex discrimination. A simplified model of phase locking showed that the substitution of sinusoids with bands of noise significantly reduced number of intervals between successive neural spikes corresponding to the virtual pitch of harmonic complex and inharmonic complex sounds. This degradation of discrimination suggests that the main source of information about the pitch of harmonic complex and inharmonic complex, especially for sinusoidal components, was the phase locking. |
DOI: 10.12693/APhysPolA.123.1106 PACS numbers: 43.66.Fe, 43.66.Hg |