The contribution of intrinsic amplitude modulation to the precedence effect at high frequencies.

Abstract

The precedence effect (PE) demonstrates our ability to locate sounds correctly at the source despite the presence of interfering sound reflections. It was shown to function with broadband noises of long duration even when lead and lag had simultaneous onsets, i.e., when information was restricted to the ongoing sound part. In a localization dominance task participants indicated the perceived location of lead-lag stimuli played from loudspeakers in an anechoic chamber. Stimuli were harmonic complex tones (HCTs) and Gaussian noise bandlimited to 2500–5500 Hz. Lead dominance existed for all stimuli despite lead and lag overlapping in time and having simultaneous onsets. This demonstrates that information from the ongoing sound part alone can evoke the PE at high frequencies. The amount of intrinsic modulation affected echo thresholds (ETs), which were slightly larger for HCTs with Schroeder positive than negative phase. Localization dominance was weak for the noise; ETs were short and a broad image was frequently reported. This indicates that the fast amplitude modulation inherent in HCTs is crucial for the PE at high frequencies, while the shallow modulation depth of the noise was likely detrimental. The PE should thus be possible for selected sounds with cochlear implants, which encode envelope information.