Temporal interactions between pure tones and amplitude-modulated noise

Abstract

An auditory interaction between the temporal fine structure of a low-frequency tone and the envelope of a high-frequency waveform was observed at very large frequency separations [in humans]. Thresholds for detection of sinusoidal amplitude modulation of a high-frequency, narrow-band noise were measured as a function of the relative phase between the modulator and a pure tone with the same frequency as the modulator. These phase functions were determined at various intensities of the noise and tone for three different modulation frequencies. In general, the phase functions showed that low-frequency stimulation has a cyclic effect on the sensitivity to amplitude modulation; over a limited range of relative phase, the modulation threshold is lower than that measured without low-frequncy stimulation whereas over a broader range of relative phases, the modulation threshold is much higher. The difference between minimum and maximum modulation thresholds was observed to be as great as 23 dB [decibel]. Despite this substantial degree of temporal interaction, little, if any, masking by the low-frequency tone of the high-freqeuncy noise was observed.