Lateralization of comodulated complex waveforms.

This study examines the ability to lateralize a complex signal characterized by correlated temporal activity across widely separated frequency regions. The high-frequency complex consisted of two narrow-band stimuli. The two stimuli had common interaural delays but different carriers centered on nonoverlapping critical bands. Two basic conditions were examined: The narrow-band stimuli had temporal envelopes which were (1) identical or (2) different. In the first experiment, narrow bands of noise were used which either had identical temporal envelopes (comodulated) or statistically independent envelopes (CFs = 2550 and 3350 Hz). In the second experiment, two sinusoidally amplitude-modulated (SAM) tones were used whose modulators either had the same starting phase or a different starting phase (CFs = 2550 and 4000 Hz). Results of the first experiment showed that for bandwidths narrower than 300 Hz, comodulated bands produced significantly lower interaural-delay thresholds compared to independent bands. Results of the second experiment showed that when the two SAM tones (100-Hz modulation rate) had the same modulator starting phase, interaural-delay thresholds were lowest.