The influence of spectral, temporal, and interaural stimulus variations on the precedence effect.

The precedence effect describes phenomena that are believed to aid localization of sounds in reverberant environments. These phenomena relate to the emphasis given to the first-arriving or preceding sound. In this paper, experiments are described which study precedence using stimulus parametrizations spanning temporal, spectral, and interaural dimensions. Subjects report the sidedness of headphone stimuli comprising a source and single reflection placed symmetrically with respect to midline. Most of the experiments use long-duration noises with the onset and offset time-of-arrival differences windowed out from the combined lead and lag stimulus, thus requiring the subject to lateralize using cues in the ongoing portion of the stimuli where the lead and lag overlap completely. A similar experiment using click stimuli is included for comparison. The influence of spectral content is studied by varying either the bandwidth or the center frequency. Dependence on interaural cues is investigated by using either ITDs or IIDs to induce laterality in the individual lead and lag components. Results indicate that precedence continues into the ongoing portion of long-duration stimuli and is robust to the removal of initial onsets, to reduction of bandwidth, and to the choice of interaural cue used to induce laterality in the lead and lag.