Lateralization of high frequency sounds as a function of interaural amplitude disparity

Twenty-five subjects made graphic ratings of the perceived lateral position within the head of sounds presented through headphones. The stimuli were high frequency, pure tones and amplitude modulated sounds. For the amplitude modulated sounds, a 200 HZ modulation frequency was combined with carrier frequencies of 2200 HZ, 3200 HZ, 4200 HZ, and 5200 HZ, which were also the pure tone frequencies. Interaural level differences in the signals ranged from zero to 12 dB. The rate of lateralization was defined as the slope of the linear trend relating laterality ratings to interaural level differences. The rate of lateralization was found to be a decreasing function of frequency. The laterality ratings of amplitude modulated signals were nearly identical to those for pure tones. This result suggests that, for high frequency signals, conflicting temporal information that a source is centered is suppressed in favor of information from level differences that the source is off-center.