2 research outputs found
Development of a method for determining binaural sensitivity to temporal fine structure.
OBJECTIVE: To develop and evaluate a test of the ability to process binaural temporal-fine-structure (TFS) information. The test was intended to provide a graded measure of TFS sensitivity for all listeners. DESIGN: Sensitivity to TFS was assessed at a sensation level of 30 dB using the established TFS-LF test at centre frequencies of 250, 500 and 750 Hz, and using the new TFS-AF test, in which the interaural phase difference (IPD) was fixed and the frequency was adaptively varied. IPDs varied from 30 to 180°. STUDY SAMPLE: Nine young (19-25 years) and 23 older (47-84 years) listeners with normal hearing over the tested frequency range. RESULTS: For the young listeners, thresholds on the TFS-AF test did not improve significantly with repeated testing. The rank-ordering of performance across listeners was independent of the size of the IPD, and moderate-to-strong correlations were observed between scores for the TFS-LF and TFS-AF tests. Older listeners who were unable to complete the TFS-LF test were all able to complete the TFS-AF test. CONCLUSIONS: No practice effects and strong correlations with an established test of binaural TFS sensitivity make the TFS-AF test a good candidate for the assessment of supra-threshold binaural processing
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Discrimination of the phase of amplitude modulation applied to different carriers: Effects of modulation rate and modulation depth for young and older subjects.
The discrimination of amplitude modulation (AM) from frequency modulation (FM) of a 1000-Hz carrier, with equally detectable AM and FM, is better for a 2-Hz than for a 10-Hz modulation rate. This might reflect greater sensitivity to temporal fine structure for low than for high rates. Alternatively, AM-FM discrimination may depend on comparing fluctuations in excitation level on the two sides of the excitation pattern, which are in phase for AM and out of phase for FM. Discrimination of the relative phase of fluctuations might worsen with increasing rate, which could account for the effect of rate on AM-FM discrimination. To test this, discrimination of the phase of AM applied to two sinusoidal carriers was assessed, with a band of noise between the two carriers to prevent use of within-channel cues. Young and older subjects with normal hearing were tested. Performance was almost constant for AM rates from 2 to 10 Hz, but worsened at 20 Hz. Performance was near chance for AM depths near the detection threshold. The results suggest that the superior AM-FM discrimination at 2 Hz cannot be explained in terms of comparison of the phase of fluctuations on the two sides of the excitation pattern