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At least 1,045 records · Page 58Linked to original sources
PubMed2001

Afferent delays and the mislocalization of perisaccadic stimuli.

Determining the precise moment a visual stimulus appears is difficult because visual response latencies vary. This temporal uncertainty could cause localization errors to brief visual targets presented before and during eye movements if the oculomotor system cannot determine the position of the eye at the time the stimulus appeared. We investigated the effect of varying neural processing time on localization accuracy for perisaccadic visual targets that differed in luminance. Although systematic errors in localization were observed, the effect of luminance was surprisingly small. We explore several hypotheses that may explain why processing delays are not more disruptive to localization performance.

Humans↗
PubMed1988

The effect of masker interaural phase on the detection of a monaural signal.

The masking-level difference (MLD) for a 500-Hz monaural pure-tone signal was examined as a function of the interaural phase shift of a 100-Hz-wide noise band centered on 500 Hz. Results indicated that the MLD decreased in magnitude as the interaural phase shift of the masker increased. In a second experiment, the 100-Hz-wide noise band was used as both the masker and the signal in order to examine the detection cues of interaural time difference and interaural level difference separately. Again, the interaural phase of the masker was varied, and an Sm signal was presented. Results indicated that the MLD decreased as a function of increasing masker interaural temporal difference for the time cue, but that the MLD did not change systematically for the level cue. The deterioration of binaural detection as a function of increasing masker interaural phase difference was not as great as that which has been reported in localization and lateralization experiments.

Auditory Perception↗
PubMed2004

Trade-offs between better hearing and better cosmetics.

A case study is reported of an adult bilateral cochlear implant patient who owns both a pair of ear-level and body-worn speech processors and chooses to wear them in unique configurations, knowingly compromising his auditory performance. The aim was to determine if differences in hearing could be quantified between these devices and to examine the size of these effects that would lend themselves to trading between performance and cosmetics. The patient reported wearing bilateral ear-level speech processors (programmed with the Cochlear Corporation spectral PEAK [SPEAK] coding strategy) 75% of the time for cosmetic and convenience reasons even though he "heard the best" with bilateral body-worn speech processors (programmed with the Cochlear Corporation advanced combination encoder strategy [ACE]). Speech perception and localization tests confirmed that this patient performed significantly better on monosyllabic phonemes in quiet (a difference from 60% to 75%) and localization (a total root-mean-squared-error difference from 22 degrees to 12degrees ) with bilateral body-worn speech processors and consistently rated various speech sounds as more clear than with bilateral ear-level units. There was a 2-dB difference in sentence reception threshold in noise, which was not statistically significant. These results suggest that clinicians should consider and provide options to patients when there are trade-offs to be made regarding understanding performance and cosmetics. Some individuals may choose better speech perception over cosmetics, and the ability to choose might result in greater compliance. The observations made here are relevant to hearing aid users as well.

Adult↗
PubMed2000

Temporal stream of cortical representation for auditory spatial localization in human hemispheres.

We measured human evoked magnetic fields to binaural sounds with an interaural time delay as a cue for auditory localization. By analyzing the topography of auditory-evoked magnetic fields in the middle-latency, we demonstrated that particular cortical regions represent the direction of sound localization by their activity level. Upon presenting a binaural sound, the first representations were found in the middle frontal region as well as the superior temporal region of the right hemisphere approximately 19 ms after the stimulation, but their patterns differed. Other cortical regions including the prefrontal and parietal spatial areas were affected within roughly 60 ms. The results showed that the right hemisphere is dominant even in the preattentive stage of auditory spatial processing of sounds from different directions.

Acoustic Stimulation↗
PubMed1980

Functional ear asymmetry in vertical localization.

Vertical frontal mid-saggital plane localization was tested in binaural, monaural left and monaural right ear conditions. Band-pass noise stimuli were presented pseudorandomly through one of four loudspeakers set with an angular separation of 11 degrees. The subject's performance, based on reaction time and mistakes, was continuously recorded. The binaural performance was twice as high as the monaural performance, suggesting that the two ears treat the information in a different and complementary way. The left ear performance was higher than the right ear performance; this strongly suggests a right hemisphere superiority for vertical localization.

Auditory Perception↗
PubMed1996

Monaural and binaural spectral cues created by the external ears of the pallid bat.

The acoustic properties of external ears transform the spectra of incident sound in a location-dependent manner, and provide monaural and binaural spectral information used in 2-dimensional localization. Human studies suggest that binaural spectral differences, and spectral peaks and notches in monaural transfer functions, may all provide spatial information. This study examined the acoustic properties of the pallid bat ear to determine directionality, interaural intensity differences spectral peaks and notches in transfer functions, as well as acoustic gain. The pallid bat is a gleaning bat that uses passive sound localization to find prey, and echolocation for general orientation. It is capable of very accurate passive sound localization, and the primary focus of this study was to determine the spectral cues that might support this localization acuity. Results show that the external ears of this bat create spectral maxima and minima that vary systematically with azimuth and elevation. The monaural spectral cues resemble those reported in humans and cats and suggest that similar spectral cues are used across taxa. The ears also create robust interaural spectral differences that vary systematically with both sound azimuth and elevation. These monaural and binaural spectral cues may provide the basis for the 1 degrees angular resolution apparent in it this bat's passive sound localization performance.

Acoustic Stimulation↗
PubMed1997

Two sources of inhibition affecting binaural evoked responses in the rat's inferior colliculus: the dorsal nucleus of the lateral lemniscus and the superior olivary complex.

The present study was undertaken to determine the influence of two extrinsic sources of inhibition on auditory binaural evoked responses recorded from the rat's inferior colliculus. The first source, the dorsal nucleus of the lateral lemniscus (DNLL), is predominantly GABAergic and has both ipsi- and contralateral projections to the central nucleus of the inferior colliculus (ICC). The second, the superior olivary complex (SOC), has a large glycinergic projection from the lateral superior olive (LSO) to the ipsilateral ICC. Thus, both structures are candidates for imposing an inhibitory effect on responses in the ICC. Neural activity was experimentally blocked by local injection of the excitatory amino acids antagonist, kynurenic acid (KYNA), into either DNLL or SOC. Binaural evoked responses were recorded from the ICC as the intensity of the sound in the ipsilateral ear was increased. Interaural intensity difference functions based on the amplitude of the evoked responses were generated before and after the KYNA injection. An injection into the contralateral DNLL greatly reduced the response suppression produced by stimulation of the ipsilateral ear. Injection into the ipsilateral DNLL, however, had no effect. Injection into the ipsilateral SOC reduced the amount of binaural suppression but the effect was apparent only in cases with surgical transection of the contralateral lateral lemniscus at a level below the DNLL. These data support the conclusion that binaural responses in the rat's ICC are shaped by inhibitory projections from both contralateral DNLL and ipsilateral SOC.

Acoustic Stimulation↗
PubMed1999

[New hearing test for functional deafness--the procedure to estimate the genuine hearing threshold].

This report describes a new procedure for examining functional deafness with binaural sound stimulation. This new hearing test can estimate the genuine pure tone hearing threshold quantitatively at every frequency by using the ordinary audiometer. In the case of the nonorganic deafness, even if the hearing disorders are bilateral or hemilateral, we believe that measuring auditory threshold separately, causes the deterioration of the threshold. Therefore, this procedure is designed so that the subject may not be aware of testing the auditory acuity of each ear, and utilizes the response of the phantom sound image in the head by simultaneous binaural presentation of sound stimulation. Our strategy is based on the following facts. If the normal subject has the same pure tone threshold level in both ears, the phantom sound image is formed in the median plane of the head by the equal suprathreshold tone level presented simultaneously in each ear. In the case of a unilateral auditory disorder, the sound image is localized to the center of the head only when sound stimulation louder than the threshold level of affected ear is given to both ears at the same time. Simultaneous binaural sound stimulation at a lower level than the threshold of the affected ear forms a lateralized sound image to the unaffected ear in the head. For patients with bilaterally similar hearing loss, the sound image is not formed if the stimulation is less than the threshold level of the pure tone. The band noise in the phase of each frequency with 50 dB HL was given binaurally to 10 normal hearing subjects, and the localization of the sound image formation was examined. This experiment confirmed that around the occipital region of the median plane in all subjects. Furthermore, comparing the formation threshold of the median plane image with the pure tone auditory threshold, proved that there was no significant difference statistically in either value. As a next step, 15 patients with unilateral sensorineural deafness were examined with this technique and we knew that the median sound images would not be formed with stimulation less than the pure tone auditory threshold of the affected ear. For clinical application, patients were classified into two groups with unilateral (6) and bilateral (2) functional deafness, and examined. Midline sound images definitely were formed with the lower magnitude of sound than the pure tone threshold by hemilateral nonorganic deafness. The difference of the forming threshold of the median sound image and the average of pure tone hearing level of the affected ear were maximum 100 dB, minimum 35 dB, and mean 69.4 dB. Furthermore, the difference of the median image forming threshold and the average hearing level of the unaffected ear were maximum 35 dB, minimum 0 dB, and mean 15.4 dB. In bilateral disorders, the midline plane sound image was formed with the corresponding level of the pure tone value in one subject, though the other one was determined by the maneuver method because it did not form a midline sound image. In conclusion, this examination can be readily used to estimate the genuine hearing threshold of the functional deafness.

Acoustic Stimulation↗
PubMed1999

Bilateral sound propagation characteristics in electronic TMJ sound recording.

Temporomandibular Joint (TMJ) sounds, clicking and crepitation, are important signs of possible TM disorder or dysfunction (TMD). The sound are usually recorded and observed by stethoscope auscultation or palpation. Sound from one TMJ may propagate through head tissues and be recorded on the contra lateral side misleading the examiner to classify both joints as non-silent. Errors in localization of sound source may lead to an erroneous diagnosis. Widmalm et al. (1997) suggested a mathematical model for estimation of the sound propagation characteristics through the head tissues. A modified model applying the auto-spectral density and cross-spectral density of the signal was used to estimate the bilateral sound propagation characteristics of temporomandibular joint sounds from two subjects. The result indicates that the head tissues act as a bandpass filter causing strong attenuation in some frequency areas with little attenuation in others. The phase response of the transfer function provides a good mean to estimate the latency in time between sounds.

Humans↗
PubMed1994

Auditory localizing acuity during acute exposure to altitude.

We have investigated the effects of hypoxia in an altitude chamber on auditory localization. Ten volunteers were tested at 18,000 ft (5,486 m), and through 12,000, 8,000, and 5,000 ft (3,657, 2,438, and 1,524 m) with directional sounds recorded via a dummy head microphone and presented binaurally. The sequence encompassed the horizontal plane. We found large intersubject variation in the response to altitude but absolute error (unsigned error) was always increased: at 18,000 ft the mean effect for the group was highly significant (p < 0.00001). The effect persisted during descent (p < 0.001 at 12,000 ft). Directional bias (mean signed error) was also substantially affected in four subjects, in that sounds originally presented in the lateral quadrants were mislocated further to the rear (p < 0.05). The incidence of front/behind confusion was not affected by altitude. We discuss these findings in relation to the proposed use of directional sounds for flight navigation and warning systems.

Adult↗
PubMedDate not supplied

How plastic is spatial hearing?

The location of a sound source is derived by the auditory system from spatial cues present in the signals at the two ears. These cues include interaural timing and level differences, as well as monaural spectral cues generated by the external ear. The values of these cues vary with individual differences in the shape and dimensions of the head and external ears. We have examined the neurophysiological consequences of these intersubject variations by recording the responses of neurons in ferret primary auditory cortex to virtual sound sources mimicking the animal's own ears or those of other ferrets. For most neurons, the structure of the spatial response fields changed significantly when acoustic cues measured from another animal were presented. This is consistent with the finding that humans localize less accurately when listening to virtual sounds from other subjects. To examine the role of experience in shaping the ability to localize sound, we have studied the behavioural consequences of altering binaural cues by chronically plugging one ear. Ferrets raised and tested with one ear plugged learned to localize as accurately as control animals, which is consistent with previous findings that the representation of auditory space in the midbrain can accommodate abnormal sensory cues during development. Adaptive changes in behaviour were also observed in adults, particularly if they were provided with regular practice in the localization task. Together, these findings suggest that the neural circuits responsible for sound localization can be recalibrated throughout life.

Animals↗