Modulation masking produced by a low-frequency pure tone

An intense low-frequency tone can affect the perception of amplitude modulation (AM) applied to a high-frequency carrier. Here, thresholds for detecting AM of a 30 0 0-Hz carrier were measured in the presence of a 50-Hz pure tone at 91 dB SPL. When the carrier was presented at 20 dB sensation level (SL), the thresholds were higher than in the absence of the 50-Hz tone, increased when the AM frequency was increased from 20 to 100 Hz, and did not show a maximum near 50 Hz, as would be expected if the effect of the 50-Hz tone resulted from modulation detection interference. When the AM frequency was fixed at 50 Hz, the AM detection thresholds showed a minimum when the phase of the AM was 90 degrees ahead of the phase of the 50-Hz tone (denoted Delta phi = 90 degrees) and a maximum for Delta phi = 270 degrees. To assess the role of the outer hair cells (OHCs), AM detection thresholds were measured as a function of Delta phi using SLs of 20 and 50 dB for normal-hearing participants and 20 dB for hearing-impaired participants. It was assumed that the latter would have impaired OHC function. The pattern of the results was similar across SLs and groups: AM detection thresholds were 8-10 dB lower for Delta phi = 90 degrees than for Delta phi = 270 degrees in all cases. This suggests that the OHCs do not play a large role in these effects and supports the idea that the low-frequency tone biases the responses of inner hair cells tuned to high frequencies.(c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )