Abstract:
Modulation detection thresholds for sinusoidal carriers were obtained for a wide range of modulation rates (10--1600 Hz) as a function of carrier frequency (1, 3, 5, 8, and 10 kHz) and carrier level (30, 45, 60, and 75 dB SPL). At low modulation rates, between 10 and about 100 Hz, thresholds were roughly constant. For higher modulation rates, thresholds were dependent on carrier frequency. For the lowest carrier frequency (1 kHz), the modulation sidebands were already spectrally resolved at a modulation rate of 100 Hz and thus thresholds decreased with increasing modulation rate. For the higher carrier frequencies, the sidebands were resolved only at higher modulation rates, due to the increasing auditory-filter bandwidth. In these cases, thresholds initially increased with increasing modulation rate with a slope of about 8 dB/oct. The threshold curves show a different shape than those obtained with broadband noise carriers. In general, thresholds decreased with increasing carrier level at any given carrier frequency up to at least 60 dB SPL. For one subject a saturation of thresholds at medium carrier levels was observed. At very low carrier levels of 20 dB SL, thresholds tended to increase with increasing modulation rate already below 100 Hz.