Unmasking produced by combination tones

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Abstract
Interactions between combination tones (CT) and unmasking were investigated. Data were obtained from 9 normal-hearing human listeners in a forward-masking paradigm in which a 2000 Hz, 35 dB SPL masker preceded a 2000 Hz test signal. This measurement provided a baseline. When a 2nd sinusoid, the suppressor, of variable frequency and 55 dB SPL was presented concurrently with the masker, the amount of masking could be less than in the baseline condition. This 2-tone unmasking was observed when the suppressor was approximately 2300 Hz. In the cubic difference tone (CDT) condition, 2 higher-frequency sinusoids of 80 dB SPL (with the lower frequency fixed at 2800 Hz) were added to the masker. In the difference tone (DT) condition, 2 higher-frequency sinusoids of 100 dB SPL (with the lower frequency fixed at 3500 Hz) were added to the masker. None of these sinusoids produced unmasking when presented individually, but when the CDT and DT were approximately 2300 Hz, unmasking was observed. The unmasking produced by the CT was similar in its frequency characteristics to that of the single, suppressor tone. Unmasking can be produced by CT, just as if CT were present in the stimulus. CT may be present in the form of traveling waves propagated along the basilar membrane.

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