Lateralization of rectangularly modulated noise: explanations for counterintuitive reversals.

A number of years ago Hafter and Shelton [J. Acoust. Soc. Am. Suppl. 1 68, S16 (1980), Hafter and Shelton, J. Acoust. Soc. Am. 90, 1901-1907 (1991)] demonstrated that diotic bandpass noise that is multiplied by a dichotic pair of periodic rectangular gating functions could be strongly perceived toward the ear receiving the signal with the gating function that is lagging in time. These results were surprising because sounds presented with interaural time delays (ITDs) are normally perceived toward the ear receiving the signal that is leading in time. In order to better understand these counterintuitive phenomena an analytical expression for the cross-correlation function of these gated-noise stimuli is derived, and it is shown that many of the general properties of the data can be accounted for by considering only the properties of this function. The lateralization of the gated-noise stimuli is compared to predictions of three types of models of binaural signal processing: models based on the cross-correlation function of the entire signal, models based on the interaural group delay or phase delay at low frequencies, and the position-variable model, which is based on the response of the peripheral auditory system to the stimuli. It is shown that the observed lateralization results, including the unexpected reversals and various frequency effects, can be explained without further assumption by an extended implementation of the position-variable model [Stern and Colburn, J. Acoust. Soc. Am. 64, 127-140 (1978)]. The cross-correlation functions of the original stimuli can also be related to the lateralization data, but in a much less natural fashion. It is argued that models based on the interaural group delay of the original stimuli will not describe the observed results, although low-frequency phase delay is qualitatively consistent with the observed lateralization phenomena.