Human sound localization at near-threshold levels
Central Systems Laboratory, Kresge Hearing Research Institute, 1301 E. Ann Street, Ann Arbor, MI 48109-0506, USA. Hearing Research
(Impact Factor: 2.97).
02/2005; 199(1-2):124-34. DOI: 10.1016/j.heares.2004.08.001
Physiological studies of spatial hearing show that the spatial receptive fields of cortical neurons typically are narrow at near-threshold levels, broadening at moderate levels. The apparent loss of neuronal spatial selectivity at increasing sound levels conflicts with the accurate performance of human subjects localizing at moderate sound levels. In the present study, human sound localization was evaluated across a wide range of sensation levels, extending down to the detection threshold. Listeners reported whether they heard each target sound and, if the target was audible, turned their heads to face the apparent source direction. Head orientation was tracked electromagnetically. At near-threshold levels, the lateral (left/right) components of responses were highly variable and slightly biased towards the midline, and front vertical components consistently exhibited a strong bias towards the horizontal plane. Stimulus levels were specified relative to the detection threshold for a front-positioned source, so low-level rear targets often were inaudible. As the sound level increased, first lateral and then vertical localization neared asymptotic levels. The improvement of localization over a range of increasing levels, in which neural spatial receptive fields presumably are broadening, indicates that sound localization does not depend on narrow spatial receptive fields of cortical neurons.
Available from: jn.physiology.org
- "Note that the bandwidths of the BL noise used here were broader than what are normally used for narrow-band sound (e.g., wider than the critical band). According to the duplex theory, this arrangement ensured that the low frequency covered only the ITD cue, the mid frequency had some ITD but mostly ILD cue, and the high frequency had both ILD and spectral cues (see Fig. 11 in Sabin et al. 2005; see DISCUSSION for the limitation of the duplex theory and the possible role of envelope ITD cue). The overall sound level of the BB noise masker was fixed at 50 dB SPL. "
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ABSTRACT: Forward masking is traditionally measured with a detection task in which the addition of a preceding masking sound results in an increased signal-detection threshold. Little is known about the influence of forward masking on localization of free-field sound for human or animal subjects. Here we recorded gaze shifts of two head-unrestrained cats during localization using a search-coil technique. A broadband (BB) noise masker was presented straight ahead. A brief signal could come from one of the 17 speaker locations in the frontal hemi-field. The signal was either a BB or a band-limited (BL) noise. For BB targets, the presence of the forward masker reduced localization accuracy at almost all target levels (20 to 80 dB SPL) along both horizontal and vertical dimensions. Temporal decay of masking was observed when a 10-ms inter-stimulus gap was added between the end of the masker and the beginning of the target. A large effect of forward masking was also observed for BL targets with low (0.2-2 kHz) and mid (2-7 kHz) frequencies, indicating that the interaural timing cue is susceptible to forward masking. Except at low sound levels, a small or little effect was observed for high-frequency (7-15 kHz) targets, indicating that the interaural level and the spectral cues in that frequency range remained relatively robust. Our findings suggest that different localization mechanisms can operate independently in a complex listening environment.
Available from: Timos Papadopoulos
- "Our expectation was that level would have a weak effect for levels above 45 dBA (e.g. Sabin et al., 2005). "
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ABSTRACT: Echolocation offers a promising approach to improve the quality of life of people with blindness although little is known about the factors influencing object localisation using a 'searching' strategy. In this paper, we describe a series of experiments using sighted and blind human listeners and a 'virtual auditory space' technique to investigate the effects of the distance and orientation of a reflective object and the effect of stimulus bandwidth on ability to identify the right-versus-left position of the object, with bands of noise and durations from 10-400 ms. We found that performance reduced with increasing object distance. This was more rapid for object orientations where mirror-like reflection paths do not exist to both ears (i.e. most possible orientations); performance with these orientations was indistinguishable from chance at 1.8 m for even the best performing listeners in other conditions. Above-chance performance extended to larger distances when the echo was artificially presented in isolation, as might be achieved in practice by an assistive device. We also found that performance was primarily based on information above 2 kHz. Further research should extend these investigations to include other factors that are relevant to real-life echolocation.
Available from: Alexandra A Ludwig
- "absolute localization tasks) [Good and Gilkey, 1996; Abel et al., 2000], and (2) spatial discrimination , i.e. the ability to discriminate different sound source locations, is measured using the minimum audible angle (MAA) paradigm [Mills, 1958; Strybel and Fujimoto, 2000; Croghan and Grantham, 2010]. To date, published data mostly refer to the spatial hearing abilities of adults [Makous and Middlebrooks, 1990; Perrott and Saberi, 1990; Middlebrooks and Green, 1991; Blauert, 1997; Sabin et al., 2005]. Respective data for children are rather sparse, and were mostly collected as mere comparative data for studies on children with hearing impairments or cochlear implants [Bess et al., 1986; Beijen et al., 2010]. "
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ABSTRACT: The present study investigated the development of two parameters of spatial acoustic perception in children and adolescents with normal hearing, aged 6-18 years. Auditory localization accuracy was quantified by means of a sound source identification task and auditory spatial discrimination acuity by measuring minimum audible angles (MAA). Both low- and high-frequency noise bursts were employed in the tests, thereby separately addressing auditory processing based on interaural time and intensity differences. Setup consisted of 47 loudspeakers mounted in the frontal azimuthal hemifield, ranging from 90° left to 90° right (-90°, +90°). Target signals were presented from 8 loudspeaker positions in the left and right hemifields (±4°, ±30°, ±60° and ±90°). Localization accuracy and spatial discrimination acuity showed different developmental courses. Localization accuracy remained stable from the age of 6 onwards. In contrast, MAA thresholds and interindividual variability of spatial discrimination decreased significantly with increasing age. Across all age groups, localization was most accurate and MAA thresholds were lower for frontal than for lateral sound sources, and for low-frequency compared to high-frequency noise bursts. The study also shows better performance in spatial hearing based on interaural time differences rather than on intensity differences throughout development. These findings confirm that specific aspects of central auditory processing show continuous development during childhood up to adolescence.
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