Counterintuitive reversals in lateralization using rectangularly modulated noise.

Listeners were required to detect an interaural delay of 37.5 microseconds in the modulation envelope of a pulse-modulated noise. The noise carrier had a bandwidth of 1000 Hz and a center frequency (fc) that varied from 550-9600 Hz. The modulation frequency was either 250, 500, or 1000 Hz and the pulse widths were either 100, 200, or 400 microseconds. For certain combinations of fc and pulse widths, unexpected results occurred when the side of the perceived image did not agree with the side stimulated first. Lateralizations of these stimuli were found to oscillate from the leading side to the lagging depending on the number of cycles of the carrier falling within a single pulse, seemingly indicating the importance of the stimulus' fine structure. Furthermore, conditions that either limited the bandwidth of the stimuli or masked portions of its spectrum show that the oscillations depended on information in the low-frequency regions. A cross-correlation model that emphasizes both the positive and negative peaks in the cross-correlations functions is shown to describe the basic phenomena.