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At least 109 records · Page 6Linked to original sources
PubMed1991

A blind mobility aid modeled after echolocation of bats.

A new model of a mobility aid for the blind was designed using microprocessor and ultrasonic devices. This mobility aid was evaluated based on psychophysical experiments. In this model, a downswept FM ultrasound signal is emitted from a transmitting array with broad directional characteristics in order to detect obstacles. The ultrasound reflections from the obstacles are picked up by a two-channel receiver. The frequency of the emitted ultrasound is swept from 70 to 40 kHz within 1 ms, so it has almost the same characteristics as the ultrasound a bat produces for echolocation. The frequency of the reflected ultrasound wave is down converted by about 50:1 by using a microcomputer with A/D and D/A converters. These audible waves are then presented binaurally through earphones. In this method obstacles may be perceived as localized sound images corresponding to the direction and the size of the obstacles. From the results of psychophysical experiments, it was found that downswept FM ultrasound was superior for the recognition of small obstacles compared to other ultrasonic schemes. With it a blind person can recognize a 1-mm-diameter wire. It was also proved that the blind could discriminate between several obstacles at the same time without any virtual images. This mobility aid, modeled after the bat's echolocation system, is very effective at detecting small obstacles placed in front of the head.

Animals↗
PubMed1992

Localization of sound in the vertical plane with and without high-frequency spectral cues.

Binaural localization of 3.0-kHz high- and lowpass noise presented in the median vertical plane (MVP) and lateral vertical plane (LVP) was investigated. We anticipated superior performance when localizing the highpass noise by virtue of the availability of pinna cues. The viability of this supposition was strengthened by monaural localization tests in which performance proficiency for the highpass noise exceeded that for the lowpass noise (p less than .01). The main result showed that binaural localization of proficiency for highpass noise surpassed that for lowpass noise for all listening conditions (p less than .01). However, the importance of binaural temporal and level differences in vertical-plane localization was demonstrated by the highly respectable performances when the lowpass noise was presented in the LVP. Data from binaural localization in the MVP and monaural localization in the LVP suggested that the influence of pinna cues diminishes for source elevations above 45 degrees.

Adult↗
PubMed1987

Infants' localization of sounds in the median sagittal plane: effects of signal frequency.

The purpose of this research was to determine if infants, like adults, show differential localization performance in the median sagittal plane (MSP) as a function of the spectrum of the signal. Infants 6-18 months of age were seated in a dark room facing an array of nine loudspeakers, with one loudspeaker positioned at ear level, 0 degrees, and four each positioned above and below ear level at 4 degrees, 8 degrees, 12 degrees, and 16 degrees. A two-alternative, forced-choice procedure was used in which a sequence of noise bursts was presented at 0 degrees and then shifted vertically, above or below 0 degrees, and continued to be presented until the infant made a directional head and/or eye movement; correct responses were visually reinforced. For each of three bandpass noise conditions (less than 4 kHz, 4-8 kHz, 8-12 kHz), minimum audible angle (MAA) for each listener, i.e., the smallest of the four angular shifts in vertical sound location that the listener could reliably detect, was estimated. Results indicated that MAA systematically decreased with increasing age, revealing an increasingly finer partitioning of auditory space. Moreover, performance at each age revealed the importance of high frequencies for localization in the MSP. Infants did not reliably localize the low-pass signal (less than 4 kHz) and showed the best performance to the signal comprising the highest frequencies (8-12 kHz). These findings reveal systematic age-related improvements in sound localization abilities during infancy, and suggest that spectral cues similar to those for adults operate for infants in vertical localization.

Auditory Perception↗
PubMed1991

Stretched and upside-down maps of auditory space in the optic tectum of blind-reared owls; acoustic basis and behavioral correlates.

Vision during early life plays an important role in calibrating sound localization behavior. This study investigates the effects of visual deprivation on sound localization and on the neural representation of auditory space. Nine barn owls were raised with eyelids sutured closed; one owl was congenitally anophthalmic. Data from these birds were compared with data from owls raised with normal visual experience. Sound localization behavior was significantly less precise in blind-reared owls than in normal owls. The scatter of localization errors was particularly large in elevation, though it was abnormally large in both dimensions. However, there was no systematic bias to the localization errors measured over a range of source locations. This indicates that the representation of auditory space is degraded in some way for blind-reared owls, but on average is properly calibrated. The spatial tuning of auditory neurons in the optic tectum was studied in seven of the blind-reared owls to assess the effects of early visual deprivation on the neural representation of auditory space. In normal owls, units in the optic tectum are sharply tuned for sound source location and are organized systematically according to the locations of their receptive fields to form a map of auditory space. In blind-reared owls, the following auditory properties were abnormal: (1) auditory tuning for source elevation was abnormally broad, (2) the progression of the azimuths and elevations of auditory receptive fields across the tectum was erratic, and (3) in five of the seven owls, the auditory representation of elevation was systematically stretched, and in the two others large portions of the representation of elevation were flipped upside down. The following unit properties were apparently unaffected by blind rearing: (1) the sharpness of tuning for sound source azimuth, (2) the orientation of the auditory representation of azimuth, and (3) the mutual alignment of the auditory and visual receptive fields in the region of the tectum representing the area of space directly in front of the animal. The data demonstrate that the brain is capable of generating an auditory map of space without vision, but that the normal precision and topography of the map depend on visual experience. The space map results from the tuning of tectal units for interaural intensity differences (IIDs) and interaural time differences (ITDs; Olsen et al., 1989).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1985

Localization of sound in rooms, II: The effects of a single reflecting surface.

Auditory localization was studied in a room bounded by a single acoustically reflective surface. The position of that surface was varied so as to stimulate a floor, a ceiling, and left and right side walls. The surface was eliminated in one condition so that we could examine localization in free field for purposes of comparison. Using a source identification method we assessed the influences of these various room configurations on the localization of both slow-onset and impulsive sine tones of low frequency (500 Hz). We also measured the steady-state interaural-time-difference (ITD) and interaural-intensity-difference (IID) cues available to subjects in the different room configurations and compared these data with the perceptual judgments. Our results indicate the following: (1) A sound must include transients if the precedence effect is to operate as an aid to its localization in rooms. (2) Even if transients are present the precedence effect does not eliminate all influences of room reflections. (3) Due to the interference of reflections large interaural intensity differences may occur in a room and these have a considerable influence on localization; this is true even at low frequencies for which IID cues do not exist in a free field. (4) Listeners appear to have certain expectations about the reliability and plausibility of various directional cues and perceptually weight the cues accordingly; we suggest that this may explain, in part, the large variation in time-intensity trading ratios reported in the literature and also the differing reports regarding the importance of onsets for localization. (5) In this study we find that onset cues are of some importance to localization even in free field.

Acoustic Stimulation↗
PubMed1990

Tracking of a "moving" fused auditory image under conditions that elicit the precedence effect.

Pursuit auditory tracking of a fused auditory image (FAI), based on stimulus conditions known to elicit the precedence effect phenomenon in sound localization, was investigated in 36 normal subjects and in a small group of subjects with known neuropathology. Movement of the FAI was simulated by incrementally varying the delay between two clicks presented, one each, from two loudspeakers placed on opposite sides of the listener. The group of normal listeners tracked the movement of the FAI without difficulty and with great accuracy; the perceived location of the FAI varied linearly with the interspeaker delay. The sensitivity of the task in detecting neural timing or integration deficits was investigated in 5 subjects with neuropathology, including subjects with unilateral temporal lobe lesions, multiple sclerosis, or dyslexia. These disorders, previously shown to disrupt neural timing, yielded characteristic patterns of tracking inaccuracy for this task. These subjects had no difficulty localizing either a moving unitary click source or sounds in daily life. These data support the suggestion that sound localization using stimulus conditions known to elicit the precedence effect places greater demands on neural timing and integration than conventional tests of localization, and may provide a more sensitive index of neural function.

Acoustics↗
PubMed1988

The contribution of the near and far ear toward localization of sound in the sagittal plane.

Eight listeners were required to locate a train of 4.5-kHz high-pass noise bursts emanating from loudspeakers positioned +/- 30, +/- 20, +/- 10, and 0 deg re: interaural axis. The vertical array of loudspeakers was placed at 45, 90, and 135 deg left of midline. The various experimental conditions incorporated binaural and monaural listening with the latter utilizing the ear nearest or ear farthest from the sound source. While performance excelled when listening with only the near ear, the contribution of the far ear was statistically significant when compared to localization performance when both ears were occluded. Based on head related transfer functions for stimuli whose bandwidth was 1.0 kHz, four spectral cues were selected as candidates for influencing location judgments. Two of them associated relative changes in energy across center frequencies (CFs) with vertical source positions. The other two associated an absolute minimum (maximum) energy for specific CFs with a vertical source position. All but one cue when measured for the near ear could account for localization proficiency. On the other hand, when listening with the far ear, maximum energy at a specific CF outperformed the remaining cues in accounting for localization proficiency.

Acoustic Stimulation↗
PubMedDate not supplied

[Hearing function in patients with disseminated sclerosis].

The hearing function in 32 patients with various forms of disseminated sclerosis was measured. Their hearing sensitivity, loudness and discrimination as well as spatial hearing and ability to localize sound sources were determined. In the absence of changes in hearing sensitivity, loudness and discrimination all the patients displayed marked disorders or complete loss of their capability to localize sound sources in the vertical plane but retained their capability to localize sound sources in the horizontal plane. Therefore, in contrast to the widely recognized concept that the hearing function in patients with disseminated sclerosis remains intact, spatial hearing impairment should be viewed as a pathognomonic symptom which is very important for diagnosing it at all stages of its development, including the earliest stages.

Adolescent↗
PubMed1986

Localization of sound in rooms, III: Onset and duration effects.

The steady-state sound field of a sine tone does not provide useful localization information in a room. Nevertheless, listeners can localize a sine tone in a room if it has an onset transient which allows the precedence effect to operate. In the present study, we made a quantitative assessment of onsets and the precedence effect by systematically varying onset duration from 0 s (impulsive), where the precedence effect is maximal, to 5 s, where there is no precedence effect at all. We also assessed listeners' sensitivity to the steady-state sound field under impulsive conditions by varying the total duration of tone pulses. Our experiments were conducted in a room with a single acoustical reflection having various directions and delays, and in an anechoic room. The results for tones of various frequencies (500 and 2000 Hz) and sound-pressure levels (65 and 40 dBA) indicate the following: Localization in rooms is facilitated by onsets even if the onsets are as long as 100 ms. The facilitation depends upon the peak intensity of the tone, as well as the onset duration, suggesting that onset rate is critical for the precedence effect; our results are most consistent with rate expressed as an increase in sound pressure per unit time. The facilitation also depends upon the reflection delay time for a room; gradual onsets take on much more importance for the precedence effect in rooms with long delays. As onsets begin to lose their effectiveness listeners become increasingly "misdirected" by invalid cues in the steady-state sound field. The pattern of misdirection suggests a perceptual averaging of cues over an interval more than an order of magnitude longer than previous estimates of the summation window for the precedence effect. The pattern of misdirection varies with the frequency of a tone, due to frequency-dependent interference effects in a room, but it is independent of signal level. Localization of an impulsive sine tone in rooms is very insensitive to the pulse duration; this suggests that binaural inhibition models of the precedence effect must be supplemented by an evaluative component that we term the "plausibility hypothesis."

Acoustic Stimulation↗
PubMed1987

Infants' localization of sounds in the horizontal plane: effects of auditory and visual cues.

Infants 6, 9, 12, 15, and 18 months were seated in a dark room facing a semicircular array comprising 10 loudspeakers, 5 to their right and left at 18 degrees, 36 degrees, 54 degrees, 72 degrees, and 90 degrees from midline. Each infant received 2 types of trials: auditory-alone trials (only a sequence of 8 clicks played), and auditory-visual trials (following the first 4 clicks, a light display at the location of the loudspeaker was activated and remained on for the remaining 4 clicks). Calibration markers on the infant's head were used to measure azimuth error (i.e., the discrepancy between the angle of head turn and loudspeaker location). For auditory-visual trials, all infants turned their head within 4 degrees-6 degrees of the sound source; there was no effect of age or loudspeaker location. For auditory-alone trials, there were significant age differences in performance, with a systematic decrease in discrepancy angle with increasing age. By 18 months there was no difference in performance as a function of localization cue.

Attention↗
PubMed1989

Directional sensitivity of sound-pressure levels in the human ear canal.

Changes in sound pressures measured in the ear canal are reported for broadband sound sources positioned at various locations about the subject. These location-dependent pressures are one source of acoustical cues for sound localization by human listeners. Sound source locations were tested with horizontal and vertical resolution of 10 degrees. Sound levels were measured with miniature microphones placed inside the two ear canals. Although the measured amplitude spectra varied with the position of the microphone in the ear canal, it is shown that the directional sensitivity at any particular frequency of the broadband stimulus is independent of microphone position anywhere within the ear canal. At any given frequency, the distribution of sound pressures as a function of sound source location formed a characteristic spatial pattern comprising one or two discrete areas from which sound sources produced maximum levels in the ear canal. The locations of these discrete areas varied in horizontal and vertical location according to sound frequency. For example, around 8 kHz, two areas of maximum sensitivity typically were found that were located laterally and were separated from each other vertically, whereas, around 12 kHz, two such areas were found located on the horizontal plane and separated horizontally. The spatial patterns of sound levels were remarkably similar among different subjects, although some frequency scaling was required to accommodate for differences in the subjects' physical sizes. Interaural differences in sound-pressure level (ILDs) at frequencies below about 8 kHz tended to increase monotonically with increasing distance of the sound source from the frontal midline and tended to be relatively constant as a function of vertical source location. At higher frequencies, however, ILDs varied both with the horizontal and with the vertical location of the sound source. At some frequencies, asymmetries between the left and right ears in a given subject resulted in substantial ILDs even for midline sound sources. These results indicate the types of horizontal and vertical spatial information that are available from sound level cues over various ranges of frequency and, within a small subject population, indicate the nature of intersubject variability.

Acoustic Stimulation↗
PubMed1991

Directional hearing in the gray tree frog Hyla versicolor: eardrum vibrations and phonotaxis.

1. We used laser vibrometry to study the vibrational frequency response of the eardrum of female gray tree frogs for different positions of the sound source in three-dimensional space. Furthermore, we studied the accuracy of 3-D phonotaxis in the same species for sounds with different frequency contents. 2. The directionality of the eardrum was most pronounced in a narrow frequency range between 1.3 and 1.8 kHz. 3. The average 3-D, horizontal and vertical jump error angles for phonotactic approaches with a sound similar to the natural advertisement call (1.1 and 2.2 kHz frequency components) were 23 degrees, 19 degrees and 12 degrees, respectively. 4. 3-D jump error angle distributions for the 1.4 + 2.2 kHz, 1.0 kHz and 2.0 kHz sounds were not significantly different from that for the 1.1 + 2.2 kHz sound. 5. The average 3-D jump error angle for the 1.4 kHz sound was 36 degrees, and the distribution was significantly different from that for the 1.1 + 2.2 kHz sound. Hence, phonotactic accuracy was poorer in the frequency range of maximum eardrum directionality. 6. Head scanning was not observed and is apparently unnecessary for accurate sound localization in three-dimensional space. 7. Changes in overall sound pressure level experienced by the frog during phonotactic approaches are not an important cue for sound localization.

Acoustic Stimulation↗
PubMed1992

A precedence effect in the perception of inter-aural cross correlation.

Does the precedence effect, well known in the field of sound localization or lateralization, also apply to other percepts based on binaural processing? We have compared, with one and the same experimental paradigm, a manifestation of the traditional precedence effect in lateralization with a possible similar effect in the perception of diffuseness or compactness of a sound image. With dichotic headphone stimulation, lateralization was controlled by the inter-aural time delay (IATD), and diffuseness/compactness by the inter-aural cross correlation (IACC). The experimental paradigm rests on the principle of estimating the over-all sensation of a 20-ms noise burst, which was subdivided in two parts, with the relevant dichotic information (IATD or IACC) in the leading part being opposite to that in the trailing part. When each part is 10 ms, it is found that the overall sensation is slightly dominated by the information in the leading part, both for lateralization and for compactness/diffuseness. This dominance of the leading part can be compensated by a certain decrease of its duration and/or amplitude relative to that of the trailing part. It is found that this quantitative measure for the 'strength' of the precedence effect for the present stimulus is essentially the same for IATD and IACC, suggesting that the precedence effect does not apply exclusively to sound localization or lateralization, but to at least one other percept based on binaural processing as well, namely the processing of inter-aural cross correlation.

Acoustic Stimulation↗
PubMed1989

Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl.

In this study we have investigated the processing of auditory cues for sound localization in the great horned owl (Bubo virginianus). Previous studies have shown that the barn owl, whose ears are asymmetrically oriented in the vertical plane, has a 2-dimensional, topographic representation of auditory space in the external division of the inferior colliculus (ICx). As in the barn owl, the great horned owl's ICx is anatomically distinct and projects to the optic tectum. Neurons in ICx respond over only a small range of azimuths (mean = 32 degrees), and azimuth is topographically mapped. In contrast to the barn owl, the great horned owl has bilaterally symmetrical ears and its receptive fields are not restricted in elevation. The binaural cues available for sound localization were measured both with cochlear microphonic recordings and with a microphone attached to a probe tube in the auditory canal. Interaural time disparity (ITD) varied monotonically with azimuth. Interaural intensity differences (IID) also changed with azimuth, but the largest IIDs were less than 15 dB, and the variation was not monotonic. Neither ITD nor IID varied systematically with changes in the vertical position of a sound source. We used dichotic stimulation to determine the sensitivity of ICx neurons to these binaural cues. Best ITD of ICx units was topographically mapped and strongly correlated with receptive-field azimuth. The width of ITD tuning curves, measured at 50% of the maximum response, averaged 72 microseconds. All ICx neurons responded only to binaural stimulation and had nonmonotonic IID tuning curves. Best IID was weakly, but significantly, correlated with best ITD (r = 0.39, p less than 0.05). The IID tuning curves, however, were broad (mean 50% width = 24 dB), and 67% of the units had best IIDs within 5 dB of 0 dB IID. ITD tuning was sensitive to variations in IID in the direction opposite to that expected for time-intensity trading, but the magnitude of this effect was only 1.5 microseconds/dB IID. We conclude that, in the great horned owl, the spatial selectivity of ICx neurons arises primarily from their ITD tuning. Except for the absence of elevation selectivity and the narrow range of best IIDs, ICx in the great horned owl appears to be organized much the same as in the barn owl.

Acoustic Stimulation↗
PubMed1990

Effect of bilateral auditory cortex lesions on absolute thresholds in Japanese macaques.

1. The behavioral audiograms of four Japanese macaques (Macaca fuscata) were assessed before and after receiving two-stage bilateral lesions of auditory cortex. Thresholds were assessed for each ear with the use of insertion earphones. 2. The bilateral lesions resulted in a large initial hearing loss followed by partial recovery that left the animals with a permanent hearing loss in both ears. 3. The initial hearing loss consisted of a total insensitivity to sound in the ear contralateral to the second lesion with limited hearing in the other ear. However, the animal with the most complete lesion was initially unable to hear sound in either ear. Broadband noise was often more effective in eliciting a behavioral response than tones. 4. Partial recovery occurred in all animals and was observed as early as the first week after surgery. Most of this recovery occurred during the first 3-7 wk after surgery. This rapid phase of recovery was sometimes followed by a more gradual phase although thresholds were still elevated after 94 wk. 5. The permanent hearing loss, which averaged from 30 to 44 dB, was not constant across frequency. Threshold shifts were smallest at 63 Hz and progressively increased with frequency to a maximum loss from 8 to 25 kHz with slightly less loss at 32 kHz. 6. Analysis of the psychophysical functions and threshold stability gave no indication of any nonsensory deficits in attention or vigilance. 7. These results, taken with those of previous experiments, indicate that each hemisphere is primarily involved in the detection of sound in the contralateral ear and secondarily involved in detection in the ipsilateral ear. This arrangement differs from that seen in sound localization where each hemisphere is involved with the contralateral hemifield as opposed to the contralateral ear. Thus it appears that the functional organization of auditory cortex for sound localization is different from that for the detection and identification of sound itself.

Animals↗
PubMed1992

Neural organization and responses to complex stimuli in the dorsal cochlear nucleus.

The dorsal division of the cochlear nucleus (DCN) is the most complex of its subdivisions in terms of both anatomical organization and physiological response types. Hypotheses about the functional role of the DCN in hearing are as yet primitive, in part because the organizational complexity of the DCN has made development of a comprehensive and predictive model of its input-output processing difficult. The responses of DCN cells to complex stimuli, especially filtered noise, are interesting because they demonstrate properties that cannot be predicted, without further assumptions, from responses to narrow band stimuli, such as tones. In this paper, we discuss the functional organization of the DCN, i.e. the morphological organization of synaptic connections within the nucleus and the nature of synaptic interactions between its cells. We then discuss the responses of DCN principal cells to filtered noise stimuli that model the spectral sound localization cues produced by the pinna. These data imply that the DCN plays a role in interpreting sound localization cues; supporting evidence for such a role is discussed.

Acoustic Stimulation↗
PubMed1979

Auditory cortex lesions and interaural intensity and phase-angle discrimination in cats.

1. A currently unresolved question concerning the effects of auditory decortication on sound localization is whether or not operated animals have a normal capacity for discriminating the small interaural differences in phase angle or intensity that result from the spatial separation of sound sources relative to the head. The present experiment was designed to provide data relevant to this question. 2. Four normal and three operated cats (bilateral ablations of AI, AII Ep, SII, I-T), wearing stereo headsets, were tested with an active avoidance procedure to detect reversals in the interaural phase-angle or intensity relations of binaural 1-kHz tones. For both groups of cats, the detection thresholds for interaural intensity and phase angle were found to be close to 1 dB and 5 degrees, respectively. 3. In addition, we found that both unoperated and operated cats exhibited positive transfer from the original lateralization task involving the detection of interaural reversals of phase angle or intensity to a new test, which required the cats to identify, in an absolute sense, which ear received the leading or louder signals. 4. Thus, the present investigation provides additional evidence that the neocortex has no primary sensory role in sound localization.

Animals↗