Abstract
The ability of sound-source localization in sagittal planes (along the top-down and front-back dimension) varies considerably across listeners. The directional acoustic spectral features, described by head-related transfer functions (HRTFs), also vary considerably across listeners, a consequence of the listener-specific shape of the ears. It is not clear whether the differences in localization ability result from differences in the encoding of directional information provided by the HRTFs, i.e., an acoustic factor, or from differences in auditory processing of those cues (e.g., spectral-shape sensitivity), i.e., non-acoustic factors. We addressed this issue by analyzing the listener-specific localization ability in terms of localization performance. Directional responses to spatially distributed broadband stimuli from 18 listeners were used. A model of sagittal-plane localization was fit individually for each listener by considering the actual localization performance, the listener-specific HRTFs representing the acoustic factor, and an uncertainty parameter representing the non-acoustic factors. The model was configured to simulate the condition of complete calibration of the listener to the tested HRTFs. Listener-specifically calibrated model predictions yielded correlations of, on average, 0.93 with the actual localization performance. Then, the model parameters representing the acoustic and non-acoustic factors were systematically permuted across the listener group. While the permutation of HRTFs affected the localization performance, the permutation of listener-specific uncertainty had a substantially larger impact. Our findings suggest that across-listener variability in sagittal-plane localization ability is only marginally determined by the acoustic factor, i.e., the quality of directional cues found in typical human HRTFs. Rather, the non-acoustic factors, supposed to represent the listeners' efficiency in processing directional cues, appear to be important.
Highlights
Human listeners use monaural spectral cues to localize sound sources in sagittal planes (e.g., Wightman and Kistler, 1997; van Wanrooij and van Opstal, 2005)
The acoustic factor was represented by the directional cues provided by the DTF sets of individual listeners
The non-acoustic factor was represented by the listener-specific uncertainty considered to describe processes related to the efficiency of processing the spectral cues
Summary
Human listeners use monaural spectral cues to localize sound sources in sagittal planes (e.g., Wightman and Kistler, 1997; van Wanrooij and van Opstal, 2005). This includes the ability to assign the vertical position of the source (e.g., Vliegen and van Opstal, 2004) and to distinguish between front and back (e.g., Zhang and Hartmann, 2010). The ability to localize sound sources in sagittal planes, usually tested in psychoacoustic experiments as localization performance, varies largely across listeners (Middlebrooks, 1999a; Rakerd et al, 1999; Zhang and Hartmann, 2010). When listening with DTFs of other listeners, the performance might be different, an effect we refer to in this study as the acoustic factor in sound localization
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