Binaural beats at high frequencies: Listeners' use of envelope-based interaural temporal and intensitive disparities

Two experiments were conducted in order to assess listeners' ability to utilize interaural disparities within interaurally ''mistuned'' envelopes of two-tone complexes centered at 3500 Hz. In the first experiment, listeners were required to distinguish between rightward or leftward directions of intracranial movement produced by the beat. The stimuli and experimental paradigm were designed so that such judgments would be made on the basis of the dynamically varying, envelope-based interaural temporal disparities (ITDs). In the second experiment, listeners were required only to distinguish between the presence or absence of an envelope-based binaural beat in a paradigm similar to that employed by McFadden and Pasanen [Science 190, 394-396 (1975)]. For both experiments, monaural envelope (beat) rates of between 10 and 640 Hz were employed with interaural beat rates of 0.25, 0.5, and 1.0 Hz. The data indicate that listeners are indeed capable of discriminating the direction of intracranial movement based on time-varying ITDs conveyed by the envelopes of high-frequency two-tone complexes. Changes in sensitivity produced by altering the rate of change of the ITD and/or its extent appear to be accounted for by assuming that there is a relatively simple trade-off between these two parameters. When the task is changed to one that is similar to that employed by McFadden and Pasanen [Science 190, 394-396 (1975)] such that listeners are merely required to discriminate between the presence and absence of an envelope-based interaural beat, the data appear to be accounted for quite parsimoniously by assuming that listeners base their decisions upon the presence or absence of dynamically varying interaural intensitive disparities. (C) 1996 Acoustical Society of America.