Threshold and Supra-Threshold Masking of Test Pulse Loudness Caused by Periodic Pulse Trains

Abstract

To identify indicators of temporal processing of periodic sounds, we investigated the effect of the periodicity of the masking pulse train on the temporal resolution and masking of the loudness of the test pulse, which was the first or the last in the train. Measurements were carried out on listeners with normal hearing and age-related SNHL. The test pulse delay D relative to the train was equal to the pulse repetition period T in the train (D = T). Central frequencies and frequency bands of all pulses were 4 kHz and 240 Hz, respectively. Under such conditions, the basis for detecting test pulses was believed to be their loudness. The intensity of masking pulses Im was 80 dB SPL. The period T was varied within the range of 20–150 ms, while the test pulse intensity Is varied within the range of 0–85 dB. The temporal resolution of the pulse loudness was equal to the minimal period T min, at which the listener could detect a test pulse. Threshold masking of the test pulse loudness (Is << Im) corresponded to the shift in the test pulse detection threshold, SI 0, obtained in the train presence relative to the threshold obtained in silence. If the intensities of masking and test pulses were equal, the latest pulse could not be detected, but the test pulse could be detected by increasing or decreasing its intensity. Thus, supra-threshold masking of the test pulse loudness (Is ~ Im) was estimated by the shifts, SdI U and SdI D, in the threshold intensity decrement and increment of the masked test pulse relative to the threshold intensity increment of a single masking pulse. The results showed that only SI 0 and SdI D were related to the temporal resolution of the test pulses loudness. These shifts depended both on the test pulse position relative to the train and the auditory sensitivity of listeners. The largest SI 0 and SdI D shifts were recorded at the temporal resolution threshold of the test pulse loudness, i.e., at T min. For listeners with normal hearing, T min was 25 ms, while SI 0 and SdI D shifts were, respectively, 12 and 18 dB if the test pulse was ahead of the train and 23 and 0 dB if the test pulse followed the train. In listeners with age-related hearing loss, the T min period increased up to 80–150 ms. At T of 120 ms, SI 0 and SdI D shifts were, respectively, 1 and 4 dB if the test pulse was ahead of the train and 4 and 7 dB if the test pulse followed the train. The informational significance of the Tmin, SI 0 and SdI D indicators was confirmed by their manifestations in the profiles of test pulse detection threshold dependences on the test pulse delay D (D ≠ T). The T min, SI 0 and SdI D indicators could be the characteristics of the temporal perception of periodic sounds, including speech. The causes of threshold and supra-threshold masking of the test pulse loudness at different positions of the test pulse relative to the masking pulse train are discussed.