Frequency bands for binaural interactions

Abstract

Earlier reports [Henning, J. Acoust. Soc. Am. 55, 84–90 (1974); Neutzel and Hafter, J. Acoust. Soc. Am. 56, S56(A) (1975)] have shown that temporal information derived from the envelopes of amplitude-modulated signals can be used for lateralization even when the carrier frequencies are interaurally discrepant. This study was intended to examine that fact more closely. Lateralization was measured using digitally generated bursts of amplitude-modulated tones of duration 200 msec and amplitude 40 dB SPL. A 50–1600 Hz bandpass noise with an overall level of 60 dB SPL masked low-frequency distortions, while the signals themselves were filtered at 200 Hz below and above the lower and upper sidebands. The digital methods employed allowed arbitrary choices of frequency and phase relations; consequently, inharmonic frequency relations between the modulation and carrier frequencies could be used. These were valuable, both as a precaution against monaural cues and as a means of assessing the degree of interaural spectral overlap necessary for lateralization. We find that the binaural overlap bands obtained with anharmonic stimuli are narrower than those reported for carriers which are multiples of the modulator. However, lateralization with interaurally indentical carriers is excellent, regardless of whether the carrier to modulation relation is harmonic.