Abstract
The present study evaluated auditory sensitivity to spectral modulation by determining the modulation depth required to detect modulation phase reversal. This approach may be preferable to spectral modulation detection with a spectrally flat standard, since listeners appear unable to perform the task based on the detection of temporal modulation. While phase reversal thresholds are often evaluated by holding modulation depth constant and adjusting modulation rate, holding rate constant and adjusting modulation depth supports rate-specific assessment of modulation processing. Stimuli were pink noise samples, filtered into seven octave-wide bands (0.125–8 kHz) and spectrally modulated in dB. Experiment 1 measured performance as a function of modulation depth to determine appropriate units for adaptive threshold estimation. Experiment 2 compared thresholds in dB for modulation detection with a flat standard and modulation phase reversal; results supported the idea that temporal cues were available at high rates for the former but not the latter. Experiment 3 evaluated spectral modulation phase reversal thresholds for modulation that was restricted to either one or two neighboring bands. Flanking bands of unmodulated noise had a larger detrimental effect on one-band than two-band targets. Thresholds for high-rate modulation improved with increasing carrier frequency up to 2 kHz, whereas low-rate modulation appeared more consistent across frequency, particularly in the two-band condition. Experiment 4 measured spectral weights for spectral modulation phase reversal detection and found higher weights for bands in the spectral center of the stimulus than for the lowest (0.125 kHz) or highest (8 kHz) band. Experiment 5 compared performance for highly practiced and relatively naïve listeners, and found weak evidence of a larger practice effect at high than low spectral modulation rates. These results provide preliminary data for a task that may provide a better estimate of sensitivity to spectral modulation than spectral modulation detection with a flat standard.
Highlights
Spectral information is thought to provide cues for the perception of both vowels and consonants [1,2,3,4,5]
Formants and formant transitions are associated with low-rate spectral modulation, whereas the harmonic structure of voiced speech is associated with higher-rate modulations
Sensitivity to spectral modulation has been evaluated in combination with temporal modulation [11,12,13]
Summary
Spectral information is thought to provide cues for the perception of both vowels and consonants [1,2,3,4,5]. Formants and formant transitions are associated with low-rate spectral modulation, whereas the harmonic structure of voiced speech is associated with higher-rate modulations. Speech recognition is thought to rely predominantly on relatively low-rate spectral modulations, in the region of 0.25 to 2 ripples per octave [2, 6, 7]. Sensitivity to spectral modulation predicts speech recognition among listeners with varying degrees of hearing loss and among cochlear implant users [3, 6, 8, 9]. Based on the association between speech perception and sensitivity to spectral modulation, evaluating sensitivity to spectral modulation has been proposed as a clinically useful approach for evaluating auditory performance. Sensitivity to spectral modulation has been evaluated in combination with temporal modulation [11,12,13]
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