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.
[Show abstract][Hide abstract] 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; 300. DOI:10.1016/j.heares.2013.03.005 · 2.97 Impact Factor
"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]. "
[Show abstract][Hide abstract] 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 · 1.71 Impact Factor
"for monkey F for high and low intensity stimuli, respectively). This finding opposes what has previously been observed in humans and monkeys, where low intensity stimuli were not as well localized as high intensity stimuli (e.g., Su and Recanzone, 2001; Recanzone and Beckerman, 2004; Sabin et al., 2005), and are opposite to humans using these same acoustic stimuli, where performance was statistically significantly worse for the lowest intensity stimuli as well as for locations in the rear quadrant (Miller and Recanzone, 2009). Thus, these animals were likely not using spatial information when performing the task and this result is consistent with our previous findings that the subtle differences in the behavioral task did not significantly contribute to any of the effects studied. "
[Show abstract][Hide abstract] ABSTRACT: Age-related hearing deficits are a leading cause of disability among the aged. While some forms of hearing deficits are peripheral in origin, others are centrally mediated. One such deficit is the ability to localize sounds, a critical component for segregating different acoustic objects and events, which is dependent on the auditory cortex. Recent evidence indicates that in aged animals the normal sharpening of spatial tuning between neurons in primary auditory cortex to the caudal lateral field does not occur as it does in younger animals. As a decrease in inhibition with aging is common in the ascending auditory system, it is possible that this lack of spatial tuning sharpening is due to a decrease in inhibition at different periods within the response. It is also possible that spatial tuning was decreased as a consequence of reduced inhibition at non-best locations. In this report we found that aged animals had greater activity throughout the response period, but primarily during the onset of the response. This was most prominent at non-best directions, which is consistent with the hypothesis that inhibition is a primary mechanism for sharpening spatial tuning curves. We also noted that in aged animals the latency of the response was much shorter than in younger animals, which is consistent with a decrease in pre-onset inhibition. These results can be interpreted in the context of a failure of the timing and efficiency of feed-forward thalamo-cortical and cortico-cortical circuits in aged animals. Such a mechanism, if generalized across cortical areas, could play a major role in age-related cognitive decline.
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