Localization in the Presence of Multiple Simultaneous Sounds

A number of studies have examined the effects that one or two competing sound sources have on sound localization accuracy, but little is known about sound localization in environments with large numbers of concurrent sound sources. In this experiment, we examined localization in a "sequential" localization task in which continuous independent noise sources were turned on one at a time, localized, and left on during the localization of up to 13 additional noise sources. This procedure was repeated with and without exploratory head movements, and with both rapid (rectangularly gated) and slow (1-second ramp) onsets in the newly presented stimuli. Although the results indicate that localization accuracy systematically decreased as the number of concurrent sources increased, overall localization accuracy was still above chance even in environments with 14 concurrent sound sources. Localization was modestly better for sounds with rapid onsets than for sounds with slow onsets, but only in environments with more than four concurrent sound sources. However, exploratory head movements, which are known to substantially improve the localization of isolated sound sources, had a negligible effect on localization accuracy with more than five sound sources. These results are preliminary, but they provide valuable insights into how listeners process complex auditory scenes that contain multiple concurrent sounds.