Why do transposed stimuli enhance binaural processing?: Interaural envelope correlation vs envelope normalized fourth moment.

High-frequency, "transposed" stimuli have been shown to yield enhanced processing of ongoing interaural temporal disparities (ITDs). This paper concerns determining which aspect or aspects of the envelopes of such stimuli mediate enhanced resolution of ITD. Behavioral measures and quantitative analyses utilizing special classes of transposed stimuli show that the "internal" interaural envelope correlation accounts both qualitatively and quantitatively for the enhancement. In contrast, the normalized fourth moment of the envelope (Y), which provides an index of the degree to which the envelopes of high-frequency stimuli fluctuate, does not lead to a successful accounting of the data.