Academic journal article Attention, Perception and Psychophysics

3-D Localization of Virtual Sound Sources: Effects of Visual Environment, Pointing Method, and Training

Academic journal article Attention, Perception and Psychophysics

3-D Localization of Virtual Sound Sources: Effects of Visual Environment, Pointing Method, and Training

Article excerpt

The ability to localize sound sources in three-dimensional space was tested in humans. In Experiment 1, naive subjects listened to noises filtered with subject-specific head-related transfer functions. The tested conditions included the pointing method (head or manual pointing) and the visual environment (VE; darkness or virtual VE). The localization performance was not significantly different between the pointing methods. The virtual VE significantly improved the horizontal precision and reduced the number of front-back confusions. These results show the benefit of using a virtual VE in sound localization tasks. In Experiment 2, subjects were provided with sound localization training. Over the course of training, the performance improved for all subjects, with the largest improvements occurring during the first 400 trials. The improvements beyond the first 400 trials were smaller. After the training, there was still no significant effect of pointing method, showing that the choice of either head- or manual-pointing method plays a minor role in sound localization performance. The results of Experiment 2 reinforce the importance of perceptual training for at least 400 trials in sound localization studies.

Testing the localization of sound sources requires accurate methods for the presentation of stimuli and the acquisition of subjects' responses. The acquisition method may affect the precision and accuracy of the response to the perceived sound direction and change the efficiency of the localization task. Many methods have been used in localization tasks: verbal responses (Mason, Ford, Rumsey, & De Bruyn, 2001; Wightman & Kistler, 1989); rotating a dial or drawing (Haber, Haber, Penningroth, Novak, & Radgowski, 1993); pointing with the nose (Bronkhorst, 1995; Middlebrooks, 1999; Pinek & Brouchon, 1992); pointing with the chest or finger (Haber et al., 1993); pointing with extensions of the body, like a stick, cane, or gun (Haber et al., 1993; Oldfield & Parker, 1984); pointing with a laser pointer (Lewald & Ehrenstein, 1998; Seeber, 2002); and using sophisticated computer interfaces (e.g., Begault, Wenzel, & Anderson, 2001). Haber et al. compared nine different response methods and showed the best precision for pointing methods. They compared the methods in blind subjects using pure tones and tested in the horizontal plane only. The difference between the head-pointing method and manual-pointing method (finger, gun, or stick) remains unclear for 3-D sound localization in sighted subjects. For sound localization in 3-D, the manual pointer may promise a better ability to point to high elevations, which can be difficult to access, by lifting the head and pointing with the nose. On the other hand, using the manual pointer may cause a bias in the responses in the horizontal plane, because holding the pointer in one hand creates an asymmetric pointing situation. Pinek and Brouchon found such an effect in a horizontal-plane localization task for right-handed subjects holding the manual pointer in their right hand. This disadvantage could counteract the potential advantage of manual pointing in vertical planes. A direct comparison between head- and manual-pointing methods has not been investigated for sound localization including the vertical planes. Thus, we investigated the effect of head and manual pointing on sound localization ability in 3-D space.

Many studies investigated the link between the visual and auditory senses with respect to sound localization (e.g., Lewald, Dörrscheidt, & Ehrenstein, 2000; May & Badcock, 2002; Shelton & Searle, 1980). The general finding is that the addition of visual information improves sound localization when the auditory and visual inputs provide congruent information (Jones & Kabanoff, 1975). Also, localization of visual targets has been found to improve when spatially correlated audio information is provided (Bolia, D'Angelo, & McKinley, 1999; Perrott, Cisneros, McKinley, & D'Angelo, 1996). …

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