Effect of unilateral bandwidth increase on ear dominance of dichotic chords

Abstract

When a 1650-Hz tone is presented to one ear while a 1750-Hz tone of equal intensity is presented to the other ear, most subjects report that there is a significant difference in the relative salience of the pitch of these two tones. This has been called “ear dominance” in the perception of dichotic chords [R. Efron and E. W. Yund, J. Acoust. Soc. Am. 59, 889–898 (1976)]. The present experiments were designed to neutralize or even reverse a given subject's ear dominance by increasing the bandwidth of the tone presented to his dominant ear while continuing to present a pure tone in the nondominant ear. This increase in bandwidth was accomplished by modulating, in brief, abrupt steps, the frequency of the dominant ear tone. The duration of each of the brief steady-state portions of the FM tone was random between 1.4 and 2.0 msec; its frequency was Gaussian-distributed around the selected center frequency. To make the salience of the two pitch components of a dichotic chord equal, a larger bandwidth increase was required in subjects having a stronger ear dominance. Lowering the sound pressure level of the stimuli in both ears increased the amount of bandwidth increase required. These results can be interpreted in terms of a model of binaural pitch mixing. [Work supported by the Veterans Administration.]