Modulation detection as a function of carrier frequency and level

This paper describes recent experiments investigating temporal processing in the auditory system. Subjects had to discriminate sinusoidal signals with a flat temporal envelope from those with a sinusoidal amplitude modulation. The modulation depth at threshold was measured for a wide range of carrier frequencies, carrier levels and modulation rates. For modulation rates up to 100Hz, thresholds remained constant and were the same for all centre frequencies tested. For higher rates, modulation thresholds initially increased and then decreased rapidly, reflecting the subjects' ability to resolve the sidebands spectrally. Detection thresholds generally improved with increasing carrier level. Most of these observations differ from results obtained for modulated broadband noises, and some are not consistent with published results for sinusoidal carriers.