Effects of envelope modulation rate and carrier frequency on auditory temporal modulation detection

The effects of envelope modulation rate (below 300 Hz) and pure-tone carrier frequency (below 8 kHz) on auditory temporal modulation detection ability (TMDA) are investigated through psychophysical experiments. The stimuli are sinusoidal amplitude-modulated signals with pure tone carriers. Two-alternative-forced-choice procedure with adaptive step is used. The temporal modulation transfer functions with different carrier frequencies are measured. Twenty-two normal-hearing subjects (22 to 29 years old) are recruited for this study. Experimental results show that both envelope modulation rate and carrier frequency have significant effects on TMDA. When carrier frequency is below 2 kHz, TMDA improves with the increase of modulation rate. When carrier frequency is above about 3.5 kHz, TMDA is influenced by the variation of carrier frequency, but without significant monotonic trend. When modulation rate is between 10 and 100 Hz, carrier frequency does not affect TMDA. When the modulation rate is between 150 and 300 Hz, TMDA decreases with the increase of carrier frequency until the carrier frequency is above 3.5 kHz.