Human sound localization at near-threshold levels.
ABSTRACT 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.
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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.Hearing research 03/2013; DOI:10.1016/j.heares.2013.03.005 · 2.85 Impact Factor
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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.Audiology and Neurotology 10/2012; 18(1):48-62. DOI:10.1159/000342904 · 1.85 Impact Factor
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ABSTRACT: The auditory cortex is known to be a necessary neural structure for the perception of acoustic signals, particularly the spatial location and the temporal features of complex auditory stimuli. Previous studies have indicated that there is no topographic map of acoustic space in the auditory cortex and it has been proposed that spatial locations are represented by some sort of population code. Additionally, in spite of temporal processing deficits being one of the hallmark consequences of normal aging, the temporal coding of acoustic stimuli remains poorly understood. This report will address these two issues by discussing the results from several studies describing responses of single auditory cortical neurons in the non-human primate. First, we will review studies that have addressed potential spike-rate population codes of acoustic space in the caudal belt of auditory cortex. Second, we will present new data on the neuronal responses to gap stimuli in aged monkeys and compare them to published reports of gap detection thresholds. Together these studies indicate that the alert macaque monkey is an excellent model system to study both spatial and temporal processing in the auditory cortex at the single neuron level.Hearing research 01/2011; 271(1-2):115-22. DOI:10.1016/j.heares.2010.03.084 · 2.85 Impact Factor