Free-field and virtual studies of the precedence effect in the median–sagittal plane: Duration effects

Abstract

The study of precedence in the median–sagittal plane is made difficult by poor localization ability in this plane, as well as by front–back confusions. We report on both free-field and virtual localization studies in which a source and simulated reflection are presented from two speakers chosen from an array of six, all of which are in the frontal median–sagittal plane. Subjects perform a forced-choice identification of which speaker emitted the combined stimulus. Stimuli consisted of lead–lag pairs of 1-, 10-, 25-, or 50-ms broadband noise bursts, where the onset of the reflection lags that of the source by 2 ms. Single-source cases were presented intermixed with the lead–lag paired stimuli. In the free-field condition, identification accuracy increased with duration for the single-source stimuli. For the precedence stimuli, a majority of responses is biased towards the elevation of the leading stimulus. However, details of individual performance show some evidence of response bias towards certain elevations, bimodal distributions, and perceptual averaging of lead and lag locations. Virtually presented stimuli using individualized HRTFs yielded localization judgments comparable to free-field stimuli for single-source conditions, but not for lead–lag pairs. [Work supported by NIH (DC02696 and DC00100) and ONR-MURI (Z883401).]