Auditory localization of nearby sources. III. Stimulus effects

A series of experiments has examined the auditory localization of a nearby (<1 m) sound source under-four conditions: (1) a fixed-amplitude condition where loudness-based distance cues were available; (2) a monaural condition where the contralateral ear Was occluded by an ear-plug and muff; (3) a high-pass condition where the stimulus bandwidth was 3 Hz to 15 kHz; and (4) a low-pass condition where the stimulus bandwidth was 200 Hz to 3 kHz. The results of these experiments were compared to those of a previous: experiment that measured localization performance for a nearby broadband, random-amplitude source [Brungart et al., J. Acoust, Sec. Am. 106, 1956-1968 (1999)]. Directional localization performance: in each condition was consistent with the results of previous far-field localization experiments. Distance localization accuracy improved slightly in the fixed-amplitude condition relative to the earlier broadband random-amplitude experiment, especially near the median plane. but was severely degraded in the monaural condition. Distance accuracy was also found to be highly-dependent on the low-frequency energy of the stimulus: in the low-pass condition, distance accuracy was similar to that in the broadband condition, while in the high-pass condition, distance accuracy was significantly reduced. The results suggest that low-frequency interaural level differences are the dominant auditory distance cue in the proximal region. [S0001-4966(99)01712-9].