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PubMed1996

Interaural time and level differences: integrated or separated processing?

The processing of internal differences in time (IDT) and sound pressure level (IDL) was studied by using the mismatch negativity auditory evoked potential (MMN), which is a probe of pre-attentive auditory sensory memory. In a passive oddball experiment, subjects were reading in a book while they were presented with a standard stimulus (P = 0.88) having no IDTs or IDLs and three different deviant stimuli revealing an IDT, IDL, or both IDT and IDL. The different deviants elicited MMNs of comparable latencies indicating that memory representations of the IDTs and IDLs have been established. The MMN amplitudes to the IDT-IDL deviant were larger than those to changes in either IDT or IDL only. Moreover, the time-courses, amplitudes, and topographies of the MMNs to the IDT-IDL deviants were very similar to the sum of the MMNs elicited by the IDT and IDL deviants. These findings suggest that the representations of the binaural location cues were (at least partly) processed in parallel. It is argued that separate azimuth representations exist for IDT and IDL at a cortical level.

Acoustic Stimulation↗
PubMed2006

Acoustic measurement: a tutorial for molecular biologists.

Although skilled in in vitro techniques, the molecular biologist may not understand the finer points of acoustical measurement. Measurement is necessary whenever the auditory system function is being measured using the auditory brainstem response (ABR) or distortion product otoacoustic emissions (DPOAE) or is being challenged by a noise exposure. While the theory of measuring an acoustic signal with a calibrated measuring microphone is simple, in practice, it can become complex. The present article presents guidelines for measuring acoustic stimuli which is within the abilities of a well equipped laboratory. It also presents a set of links for further information and some sources for procurement of equipment.

Acoustic Stimulation↗
PubMed2005

The hearing abilities of the prawn Palaemon serratus.

The mechanism of sound reception and the hearing abilities of the prawn (Palaemon serratus) have been studied using a combination of anatomical, electron microscopic and electrophysiological approaches, revealing that P. serratus is responsive to sounds ranging in frequency from 100 to 3000 Hz. It is the first time that the Auditory Brainstem Response (ABR) recording technique has been used on invertebrates, and the acquisition of hearing ability data from the present study adds valuable information to the inclusion of an entire sub-phylum of animals when assessing the potential impact of anthropogenic underwater sounds on marine organisms. Auditory evoked potentials were acquired from P. serratus, using two subcutaneous electrodes positioned in the carapace close to the supraesophageal ganglion and the statocyst (a small gravistatic organ located below the eyestalk on the peduncle of the bilateral antennules). The morphology of the statocyst receptors and the otic nerve pathways to the brain have also been studied, and reveal that P. serratus possesses an array of sensory hairs projecting from the floor of the statocyst into a mass of sand granules embedded in a gelatinous substance. It is the purpose of this work to show that the statocyst is responsive to sounds propagated through water from an air mounted transducer. The fundamental measure of the hearing ability of any organism possessing the appropriate receptor mechanism is its audiogram, which presents the lowest level of sound that the species can hear as a function of frequency. The statocyst of P. serratus is shown here to be sensitive to the motion of water particles displaced by low-frequency sounds ranging from 100 Hz up to 3000 Hz, with a hearing acuity similar to that of a generalist fish. Also, recorded neural waveforms were found to be similar in both amplitude and shape to those acquired from fish and higher vertebrates, when stimulated with low-frequency sound, and complete ablation of the electrophysiological response was achieved by removal of the statocyst.

Acoustic Stimulation↗
PubMed2004

Effect of an initial noise induced hearing loss on subsequent noise induced hearing loss.

The effect of previous noise induced hearing loss (NIHL) on subsequent NIHL was studied in rats. Three groups of animals were initially exposed to different durations of 113 dB SPL broad band noise (21 days, 3 days or 0 days--unexposed). Their permanent threshold shifts (PTS) from this exposure (PTS1) were evaluated using auditory nerve-brainstem evoked responses (ABR). All the animals were then noise-exposed for an additional 12 days, and the incremental PTS following this exposure (PTS2) was also assessed. The 21 day group showed the greater PTS1 [mean +/- SD: 27.03 +/- 6.78 dB, compared with 11.67 +/- 10.47 dB (3 day group)] and the lowest PTS2 [9.84 +/- 8.19 dB, compared with 13.33 +/- 14.60 dB (3 day group) and 24.04 +/- 12.4 dB (0 day group)]. This group also showed the highest total PTS and lowest SD following the two noise exposures [36.88 +/- 6.29 dB, compared with 25.00 +/- 12.68 dB (3 day group) and 26.35 +/- 11.93 dB (0 day group)]. The results may be explained by the lower effective intensity of the second noise exposure for the animals with a large PTS1 compared to those with little or no NIHL from the first noise exposure.

Animals↗
PubMed2005

Neural correlates of the precedence effect in auditory evoked potentials.

The precedence effect in subjective localization tasks reflects the dominance of directional information of a direct sound (lead) over the information provided by one or several reflections (lags) for short delays. By collecting data of both psychoacoustical measurements and auditory evoked potentials the current study aims at neurophysiological correlates for the precedence effect in humans. In order to investigate whether the stimulus features or the perception of the stimulus is reflected on the ascending stages of the human auditory pathway, auditory brainstem responses (ABRs) as well as cortical auditory evoked potentials (CAEPs) using double click-pairs were recorded. Potentials were related to the results of the psychoacoustical data. ABRs to double click-pairs with lead-lag delays from 0 to 20 ms and interaural time differences (ITDs) in the lag click of 0 and 300 micros show an emerging second wave V for lead-lag delays larger than 2 ms. The amplitudes of the first and second wave V are the same for a lead-lag delay of about 5 ms. For the lag-ITD stimuli the latency of the second wave V was prolonged by approximately ITD/2 compared to the stimuli without lag-ITD. As the amplitudes of the second wave V were not decreased for a lead-lag delay around 5 ms as could be expected from psychoacoustical measurements of the precedence effect, ABRs reflect stimulus features rather than the perceptive qualities of the stimulus. The mismatch negativity (MMN) component of the CAEP for double click-pairs was determined using a diotic standard and a deviant with an ITD of 800 micros in the lag click. The comparison between the MMN components and the psychoacoustical data shows that the MMN is related to the perception of the stimulus, i.e., to the precedence effect. Generally, the findings of the present study suggest that the precedence effect is not a result of a poor sensitivity of the peripheral bottom-up processing. Rather, the precedence effect seems to be reflected by the MMN, i.e., cognitive processes on higher stages of the auditory pathway.

Acoustic Stimulation↗
PubMed2006

A clinical analysis of psychogenic sudden deafness.

OBJECTIVE: Sudden deafness, in most cases, has no apparent cause. In some cases viral infection, vascular occlusion, or a cochlear membrane rupture may be responsible for the sudden loss of hearing. In this study, we analyzed etiology, audiologic, psychiatric, and clinical aspects of psychogenic sudden deafness through a retrospective chart review. Patients included were thought to have sudden deafness as a result of psychogenic causes and/or stresses. STUDY DESIGN AND SETTING: We reviewed the records of 277 patients who had been admitted to the Department of Otolaryngology, Kangbuk Samsung Hospital, from January 1997 to July 2003, with the initial diagnosis of idiopathic sudden hearing loss. RESULTS: In the medical history of 9 patients, there was an association between sudden onset of hearing loss and psychogenic events. There were 4 patients who had a preexisting mental health condition. A psychiatrist provided the classification of psychogenic sudden deafness for 7 patients (2.5%) who had organic causes ruled out. These patients showed discrepancy between pure tone audiometry and ABR. There were 2 males and 5 females; 4 patients were in their 10's, 1 in his 20's, and 2 in their 40's. Three patients had bilateral hearing loss and 4 had unilateral loss. The hearing test scores revealed: 4 patients with severe to profound hearing loss at 71 dB or higher, 2 patients with moderately severe hearing loss ranging from 56 to 70 dB, and 1 patient with moderate hearing loss from 41 to 56 dB. Hearing was restored in all patients, partially or completely, by treatment with steroid injections and psychotherapy. CONCLUSIONS: A total of 2.5% of sudden onset hearing loss cases in our study were a result of psychogenic causes. We observed distinctive features for audiologic measures, psychiatric findings, and clinical characteristics. The recovery rate and prognosis were better in patients who had accurate audiometry and were under the care of a psychiatrist. EBM RATING: C-4.

Adolescent↗
PubMed2000

Normal audiologic presentations in patients with acoustic neuroma: An evaluation using strict audiologic parameters.

Although several studies have previously reported on patients presenting with "normal" audiologic parameters in acoustic neuroma, the present study is, to our knowledge, the first to exclusively examine in detail cases involving exceptionally stringent objective audiometric features. Of 369 patients with acoustic neuroma who were operated on between April 1980 and April 1997 by our group, 10 had strictly normal hearing, defined as follows: (1) pure-tone average < 20 dB; (2) speech discrimination score > 90%; and (3) interaural differences </= 10 dB at every hertz level. A high level of audiologic functioning was found to significantly lower the sensitivity of auditory brainstem response in the detection of acoustic neuroma. Magnetic resonance imaging was the only preoperative test exhibiting 100% sensitivity in this setting. Thus, a high level of clinical suspicion appears warranted in any case involving unexplained unilateral audiovestibular symptoms-including those instances in which strictly normal hearing parameters exist and are associated with negative auditory brainstem response findings.

Adolescent↗
PubMed1995

Effects of contralateral white noise stimulation on transitory evoked otoacoustic emissions in patients with acoustic neuroma.

Transitory evoked otoacoustic emissions are normal phenomena observed in most persons with hearing levels greater than 35 dB. Further, masking of the contralateral ear produces amplitude reductions in the transitory evoked otoacoustic emissions. We have undertaken a study of transitory evoked otoacoustic emissions in 20 patients with acoustic neuroma. All patients were assessed for transitory evoked otoacoustic emissions bilaterally, with and without contralateral masking with white band noise at 40, 50, and 60 dB. We found that transitory evoked otoacoustic emissions were present in 30% of ears with tumor and that the presence of transitory evoked otoacoustic emissions is associated with improved preoperative hearing levels, but that tumor size is not associated with the presence or absence of transitory evoked otoacoustic emissions. The amplitude of transitory evoked otoacoustic emissions from ears with tumor, when present, is decreased when compared with normal ears of normal patients. Further, with contralateral masking little of the amplitude reduction observed in normal patients is observed in the ears with acoustic neuroma. However, with masking of the contralateral ear, the ear without tumor demonstrated significantly greater amplitude reductions than normal ears from normal patients (p = 0.0006). Pertinent anatomy and possible explanations for these findings are discussed.

Acoustic Stimulation↗
PubMed2001

The intensity of masking noise affects the mismatch negativity to speech sounds in human subjects.

The present study investigated the effects of decreased audibility of the speech sounds 'ba' and 'da' on the mismatch negativity (MMN). Audibility was altered by varying the intensity of the masking noise to be either 0 (no noise), 65, 70 or 75 dB speech perception level. Cortical event-related potentials were recorded while normal listeners (n=7) were instructed to ignore the stimuli. In a separate condition, subjects were asked to signal detection of the deviant stimulus by button-press. As audibility of speech sounds was decreased, MMN peak amplitude decreased and MMN peak latency increased. Behavioral responses were in accordance with the MMN data. Hit rates decreased as audibility decreased. These results suggest that both pre-attentive and attentive speech discrimination deteriorate following a reduction in audibility.

Acoustic Stimulation↗
PubMed2001

Severe vestibular and auditory impairment in three alleles of Ames waltzer (av) mice.

The genetic and physiological characterization of circling, hearing-impaired mouse mutants has greatly facilitated our understanding of non-syndromic sensorineural deafness, the most common form of hereditary human hearing loss. Here we report the first phenotypic characterization of three alleles of Ames waltzer (av). Neither electrical potentials (auditory brainstem response) nor behavioral responses to sound could be evoked in any of the three alleles at any age or frequency. However, the endocochlear potential was found to be normal, indicating that the primary pathology is not in the stria vascularis. To determine the earliest changes and help identify the primary causes of deafness in av, we performed morphological studies in 15-16 day old mutants, just prior to the maturation of the cochlea. Although av(2J) is slightly more affected than the other two alleles, our studies show a high similarity between all three alleles. The first detectable changes are observed in the stereocilia and cytoplasm of hair cells, and in the cellular shape and microvilli of supporting cells. These changes are followed by degeneration of the cochlear and vestibular neuroepithelium.

Alleles↗
PubMed2001

The effects of temporal asymmetry on the detection and perception of short chirps.

There is an intriguing contrast between the physiological response to short frequency sweeps in the brainstem and the perception produced by these sounds. Dau et al. (2000) demonstrated that optimised chirps with increasing instantaneous frequency (up-chirps), designed to compensate for spatial dispersion along the cochlea, enhance wave V of the auditory brainstem response (ABR), by synchronising excitation of all frequency channels across the basilar membrane. Down-chirps, that is up-chirps reversed in time, increase cochlear phase delays and therefore result in a poor ABR wave V. In this study, a set of psychoacoustical experiments with up-chirps and down-chirps has been performed to investigate how these phase changes affect what we hear. The perceptual contrast is different from what was reported at the brainstem level. It is the down-chirp that sounds more compact, despite the poor synchronisation across channels and phase delays up to 20 ms. The perceived 'compactness' of a sound is apparently more determined by the fine structure of excitation within each peripheral channel than by between-channel phase differences. This suggests an additional temporal integration mechanism at a higher stage of auditory processing, which effectively removes phase differences between channels.

Acoustic Stimulation↗
PubMed2004

Age-related hearing loss and the ahl locus in mice.

C57BL/6 (B6) mice experience hearing loss and cochlear degeneration beginning about mid-life, whereas CAST/Ei (CAST) mice retain normal hearing until old age. A locus contributing to the hearing loss of B6 mice, named age-related hearing loss (ahl), was mapped to Chromosome 10. A homozygous, congenic strain of mice (B6.CAST-+ahl ), generated by crossing B6 (ahl/ahl) and CAST (+ahl/+ahl) mice has the same genomic material as the B6 mice except in the region of the ahl locus, which is derived from CAST. In this study, we have determined the extent of the CAST-derived region of Chromosome 10 in the congenic strain and have examined mice of all three strains for hearing loss and cochlear morphology between 9 and 25 months of age. Results for B6 mice were similar to those described previously. CAST mice showed no detectable hearing loss even at 24 months of age; however, they had a small amount of ganglion cell degeneration. B6.CAST-+ahl mice were protected from early onset hearing loss and basal turn degeneration, but older animals did show some hearing loss and ganglion cell degeneration. We conclude that loci in addition to ahl contribute to the differences in hearing loss between B6 and CAST mice. These results illustrate the complex inheritance of age-related hearing loss in mice and may have implications for the study of human presbycusis.

Aging↗
PubMed1997

The envelope following response to multiple tone pair stimuli.

The envelope following response (EFR) is a steady-state evoked response which follows the envelope of a stimulating waveform. A tone pair with frequencies f1 and f2 generates a temporal envelope whose period corresponds to the difference in frequency between the constituent tones (f2-f1 = f2,1). EFRs were recorded from Mongolian gerbils using amplitude-modulated stimuli comprised of from 1 to 4 tone pairs. Five stimulus tone pairs were used having center frequencies of approximately 0.3, 1, 2, 3, and 5 kHz; their corresponding envelope frequencies were approximately 38, 55, 66, 85, and 142 Hz. The magnitude of the EFR to each tone pair was measured separately and in combination with other simultaneously presented tone pairs. Small decreases (1-3 dB) in response magnitude, relative to the single tone pair condition, resulted from the addition of 1-2 tone pairs of higher frequencies; this effect was more pronounced with the addition of a third and fourth tone pair. However, the addition of the 300 Hz tone pair resulted in the significant enhancement of the response to higher frequency tone pairs. These data indicate that multiple tone pair EFRs may be a useful technique for the rapid acquisition of frequency-specific audiometric information.

Acoustic Stimulation↗
PubMed1998

A developmental study of distortion product otoacoustic emission (2f1-f2) suppression in humans.

Suppression of the 2f1-f2 distortion product otoacoustic emission (DPOAE) provides an effective paradigm for the study of functional cochlear maturation in humans. DPOAE iso-suppression tuning curves (STCs) represent some aspect of peripheral filtering, probably related to the boundaries of distortion generation. Studies conducted thus far suggest that the cochlear tuning assessed by this technique is adult-like in humans by term birth (Abdala et al., Hear. Res. 98 (1996) 38-53; Abdala and Sininger, Ear Hear. 17 (1996) 374-385). However, there have been no studies of cochlear tuning in premature human neonates. DPOAE STCs and suppression growth functions were measured from 14 normal-hearing adults, 33 term and 85 premature neonates to investigate the developmental time course of cochlear frequency resolution and non-linearity. Premature neonates showed non-adult-like DPOAE suppression at f2 of 1500 and 6000 Hz: (1) STCs were narrower in width (Q10) and steeper in slope on the low-frequency flank of the tuning curve; (2) suppressor tones lower in frequency than f2 produced atypically shallow growth of DPOAE suppression. The influence of immature conductive pathways cannot be entirely ruled out as a factor contributing to these results. However, findings may indicate that an immaturity exists in cochlear frequency resolution and non-linearity just prior to term birth. The bases of this immaturity are hypothesized to be outer hair cell in origin.

Adolescent↗
PubMed1998

Otoconial agenesis in tilted mutant mice.

The sense of balance is one of the phylogenetically oldest sensory systems. The vestibular organs, consisting of sensory hair cells and an overlying extracellular membrane, have been conserved throughout vertebrate evolution. To better understand mechanisms regulating vestibular development and mechanisms of vestibular pathophysiology, we have analyzed the mouse mutant, tilted (tlt), which has dysfunction of the gravity receptors. The tilted mouse arose spontaneously and has not been previously analyzed for a developmental or physiological deficit. Here we demonstrate that the tilted mouse, like the head tilt (het) mouse, specifically lacks otoconia and consequently does not sense spatial orientation relative to the force of gravity. Unlike other mouse mutations affecting the vestibular system (such as pallid, mocha and tilted head), the defect in the tilted mouse is highly penetrant, results in the nearly complete absence of otoconia, exhibits no degeneration of the sensory epithelium and has no apparent abnormal phenotype in other organ systems. We further demonstrate that protein expression in the macular sensory epithelium is qualitatively unaltered in tilted mutant mice.

Animals↗
PubMed2000

Structural/audiometric correlations in a human inner ear with noise-induced hearing loss.

A morphological analysis was performed on a human cochlea removed during skull base surgery. The patient experienced a noise-induced hearing loss following 30 years of mechanical exposure. The tissue was processed according to the block surface technique and the organ of Corti, osseous spiral lamina and spiral ganglion were analyzed at different levels. There was a circumscribed lesion approx. 10 mm from the round window extending to about 13 mm. At this site, the dominant pathological feature was the loss of outer hair cells that was comprehensive in the centermost area and partial in the peripheral region of the damage. The degradation of inner hair cells was less severe with signs of cell atrophy yet with limited loss. Outer pillar cells were often collapsed leading to deformation of the acoustic ridge. The Deiters cells were often present and physically interactive with remaining nerve fibers. In the reticular lamina, surgical manipulation and dissection resulted in tears which may be attributed to a reduction of intercellular strength between cells. In the damaged area, there was a 45% loss of myelinated nerve fibers measured at the osseous spiral lamina. Pathological changes could not be observed in the spiral ganglion with certainty although the type II cells innervating the outer hair cells were often difficult to discern.

Audiometry↗
PubMed1998

Age-related changes in transiently evoked otoacoustic emissions and distortion product otoacoustic emissions in normal-hearing ears.

Age-related changes in transiently evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) were evaluated in normal-hearing ears. The TEOAE was elicited by a non-linear click with a stimulus level of 82 +/- 1 dB SPL using ILO 88 in 251 normal-hearing ears. The DPOAE at the frequency of 2f1-f2 was measured with stimulus levels of 70 dB SPL (f1) and 60 dB SPL (f2) and with an f2/f1 ratio of 1.2 using ILO 92 in 64 normal-hearing ears. The results obtained showed that TEOAE and DPOAE were decreased with increasing age. Moreover, the same pattern of gradual decrease in TEOAE and in DPOAE suggests the possibility of the same generating mechanism associated with outer hair cells (OHCs).

Acoustic Stimulation↗