Interference in detection of interaural delay in a sinusoidally amplitude-modulated tone produced by a second,...

Sensitivity to interaural time delays (ITDs) within high-frequency sinusoidally amplitude-modulated (SAM) target tones was measured in the presence of a second, spectrally remote diotic SAM tone (termed an interferer). Targets and interferers were 100% modulated at 250 Hz and each was presented at 77 dB SPL for a duration of 250 ms. The modulations of targets and interferers were either in-phase or out-of-phase. In the first experiment, when the target SAM tone was centered at 4 kHz, interferers were centered at either 500 Hz, 1 kHz, or 2 kHz. Threshold ITDs were substantially increased in the presence of the interferers as compared to when the targets were presented in isolation. The greatest effects were observed with interferers centered at 500 Hz and 1 kHz. In the second experiment, when the target SAM tone was centered at 2 kHz, interferers were centered at either 500 Hz or 4 kHz. Threshold ITDs increased in the presence of either interferer, but the greatest increase occurred in the presence of the 500-Hz SAM tone. In the third experiment, it was found that presenting the low-frequency SAM tones continuously resulted in less interference than did presenting the interferers and targets coincidently. In all three experiments, the effects produced by the interferers did not depend upon whether they were modulated in-phase or out-of-phase with the target. Taken together, the data argue against the notion that the interference could result from a peripheral, monaural interaction between target and interferer waveforms.