Recovery Of Temporary Threshold Shift Research Articles

Effects of fatiguing tone frequency on temporary threshold shift in bottlenose dolphins (Tursiops truncatus)

Temporary threshold shift (TTS) was measured in two bottlenose dolphins (Tursiops truncatus) after exposure to 16-s tones between 3 and 80 kHz to examine the effects of exposure frequency on the onset, growth, and recovery of TTS. Hearing thresholds were measured approximately one-half octave above the exposure frequency using a behavioral response paradigm featuring an adaptive staircase procedure. Results show frequency-specific differences in TTS onset and growth, and suggest increased susceptibility to auditory fatigue for frequencies between approximately 10 and 30 kHz. Between 3 and 56 kHz, the relationship between exposure frequency and the exposure level required to induce 6 dB of TTS, measured 4 min post-exposure, agrees closely with an auditory weighting function for bottlenose dolphins developed from equal loudness contours [Finneran and Schlundt. (2011). J. Acoust. Soc. Am. 130, 3124-3136].

Noise‐induced temporary threshold shift in marine mammals.

In 1996, Dave Kastak and Ron Schusterman reported the first observations of noise‐induced temporary threshold shift (TTS) in a marine mammal [D. Kastak and R. J. Schusterman, “Temporary threshold shift in a harbor seal (Phoca vitulina),” J. Acoust. Soc. Am. 100, 1905–1908 (1196)]. Since that time, a number of studies have been conducted to characterize the effects of noise on the hearing abilities of pinnipeds and odontocete cetaceans. These studies compare hearing thresholds before and after subjects are exposed to intense sounds and relate feature of the noise exposure to the observed threshold shift. The results are analogous to data from terrestrial mammals, where TTS depends on the frequency, amplitude, duration, and temporal pattern of the noise exposure, as well as the hearing test frequency and the recovery time. This talk reviews the major findings related to the growth and recovery of TTS in marine mammals, with an emphasis on recent data from high‐frequency tonal exposures in bottlenose dolphins. The relationship between onset‐TTS levels across a range of frequencies and proposed auditory weighting functions will also be discussed. [Work supported by the ONR.]

Growth and recovery of temporary threshold shift at 3 kHz in bottlenose dolphins: Experimental data and mathematical models

Measurements of temporary threshold shift (TTS) in marine mammals have become important components in developing safe exposure guidelines for animals exposed to intense human-generated underwater noise; however, existing marine mammal TTS data are somewhat limited in that they have typically induced small amounts of TTS. This paper presents experimental data for the growth and recovery of larger amounts of TTS (up to 23 dB) in two bottlenose dolphins (Tursiops truncatus). Exposures consisted of 3-kHz tones with durations from 4 to 128 s and sound pressure levels from 100 to 200 dB re 1 μPa. The resulting TTS data were combined with existing data from two additional dolphins to develop mathematical models for the growth and recovery of TTS. TTS growth was modeled as the product of functions of exposure duration and sound pressure level. TTS recovery was modeled using a double exponential function of the TTS at 4-min post-exposure and the recovery time.

Temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) exposed to intermittent tones

Temporary threshold shift (TTS) was measured in a bottlenose dolphin exposed to a sequence of four 3-kHz tones with durations of 16 s and sound pressure levels (SPLs) of 192 dB re 1 μPa. The tones were separated by 224 s of silence, resulting in duty cycle of approximately 7%. The resulting growth and recovery of TTS were compared to experimentally measured TTS in the same subject exposed to single, continuous tones with similar SPLs. The data confirm the potential for accumulation of TTS across multiple exposures and for recovery of hearing during the quiet intervals between exposures. The degree to which various models could predict the growth of TTS across multiple exposures was also examined.

Non-Linear Aspects of Outer Hair Cell Transduction and the Temporary Threshold Shifts after Acoustic Trauma

The 200-Hz cochlear microphonic potential (CM) and the compound action potential (CAP) of the auditory nerve evoked by tone-bursts were recorded in the basal turn of the cochlea of anaesthetised guinea pigs, before and after exposure to traumatic high-frequency tones that produce a temporary threshold shift (TTS) in this cochlear region. The drop in CM and the TTS were highly correlated, suggesting that it is the disruption of the outer hair cells generating the CM that causes the TTS. The previously measured rise in endocochlear potential and drop in organ of Corti K⁺ levels suggest that the TTS is due to a temporary closure of outer hair cell mechanoelectrical transduction (MET) channels, which produces a drop in the mechanical sensitivity of the organ of Corti, due to disruption of the active process provided by outer hair cells. The time course of the onset and recovery of TTS is consistent with a kinetic folding and refolding of MET channels over a time course of hours and days. Mathematical modelling of this putative channel folding suggests that TTS recovery may be accelerated by the presentation of additional sounds during the recovery period. We present electrophysiological data (CM and CAP measurements) showing that this accelerated recovery occurs. Using two-tone complexes (phase-locked 5- and 10-kHz traumatic tones, and 10-kHz traumatic tones with 25-Hz bias tones), we also show that the mechanisms producing TTS are non-linear and asymmetric, and that the greatest ‘trauma’ occurs when the hair bundles of outer hair cells are deflected away from the basal body of these cells (i.e. in the direction normally causing hyperpolarisation of the cell membrane potential).

A four-state kinetic model of the temporary threshold shift after loud sound based on inactivation of hair cell transduction channels

A model of the temporary threshold shift (TTS) following loud sound is presented based on inactivation of the mechano-electrical transduction (MET) channels at the apex of the outer hair cells (OHCs). This inactivation is assumed to reduce temporarily the OHC receptor current with a consequent drop in the mechanical sensitivity of the organ of Corti. With acoustic over-stimulation some of the hair cells' MET channels are assumed to adopt one of three closed and non-transducing conformations or `TTS states'. The sound-induced inactivation is assumed to occur because the sound makes the TTS states more energetically favourable when compared with the transducing states, and the distribution between these states is assumed to depend on the relative energies of the states and the time allowed for migration between them. By lumping the fast transducing states (one open and two closed) into a single transducing `pseudo-state', the kinetics of the inactivation and re-activation processes (corresponding to the onset and recovery of TTS) can be described by a four-state kinetic model. The model allows an elegant description of the onset and recovery of TTS time-course in a human subject under a variety of continuous exposure conditions, and some features of intermittent exposure as well. The model also suggests that recovery of TTS may be accelerated by an intermittent tone during the recovery period which may explain some variability TTS in the literature. Other implications of the model are also discussed.

Exponential onset and recovery of temporary threshold shift after loud sound: evidence for long-term inactivation of mechano-electrical transduction channels

The onset and recovery of temporary threshold shift (TTS) in one human subject (the author) has been studied during and after pure-tone overstimulation lasting between minutes and days. Under the conditions of these experiments the time courses appeared reproducible, and thresholds always recovered to normal within 3 days. The onset and recovery followed a multiple-exponential time course, with the time constants for the onset being 6.5 and 800 min, and the recovery time constants being 30, 240 and 800 min. The observed time courses were consistent with data previously reported in humans, and with the view that the threshold elevation was due to an inactivation and reactivation of the stretch-activated channels at the apex of the outer hair cells of the cochlea. The time constants of the multi-exponential onset and recovery do not appear to depend on the duration of the overstimulation, but the exponential coefficients do. A simple kinetic model of the onset and recovery is described (for more detail see Patuzzi (1998)). It is suggested that the rapid recovery in the first 5 min after exposure is due to a short-lived disruption of the synapses between the inner hair cells and the primary afferent neurones. Intermittent exposures were found to produce much less TTS than continuous tones, and this reduction was found to be inconsistent with the Equal Energy Hypothesis, in that the TTS produced by intermittent tones was much less than predicted using the Equal Energy model, and the recovery time course was also different from that expected from a shorter exposure to a continuous tone of equal energy.

Physiological and psychophysical measures from humans with temporary threshold shift.

Tuning curves and amplitude-intensity functions on wave I and wave V of the auditory-evoked brain stem response and psychophysical tuning curves were obtained from human subjects (N = 5) with noise-induced temporary threshold shift (TTS). All tuning curves were measured with the same stimuli. Maskers were pure tones presented simultaneously with the signal which was a 3.6-kHz tone pip. TTS was produced by a narrow-band noise centered at 2.6 kHz and presented at 86 dB SPL for 8 h. The maximum mean TTS was 28 dB and occurred at 3.5 kHz. Although intersubject variability of TTS was small, individual differences in other measurements were substantial. In some subjects, amplitudes of waves I and V decreased following the noise exposure with wave I typically being more affected, while in other subjects, little or no change in amplitude occurred. All tuning curves had wider response areas following noise exposure. In a given subject, changes in psychophysical and wave V tuning curves were similar and were less than changes measured for wave I. Recovery of tuning curves (low- and high-frequency side) to pre-exposure values required between 7 and 41 h depending upon the individual and preceded complete recovery of TTS.

Developmental changes of susceptibility to temporary threshold shift in hamsters

The magnitude of temporary threshold shift (TTS) and the time course of recovery of TTS were studied in young hamsters. Animals aged 15, 28, 40, 55, or 85 days were anesthetized with urethane and a sound speculum was sealed around the left tympanic ring. Evoked potentials in response to tone bursts were recorded from an electrode in the right inferior colliculus and thresholds for detecting the computer-averaged neural response were measured before and for 100 min after a 10 minute presentation of a continuous tone (3 kHz, 110 dB SPL), Mean threshold shifts at 4 kHz, 1 min post-exposure, were 16, 35, 41, 28, and 25 dB in the 15-, 28-, 40-, 55-, and 85-day-old groups respectively. Threshold shifts recovered within 100 min in 15- and 85-day-old animals, but required considerably longer to recover in the other age groups. The data suggest that young hamsters pass through a critical period of susceptibility to TSS. Consideration of the development of normal thresholds suggests that the critical period may be dependent on developmental changes within the cochlea. [Work supported by the Deafness Research Foundation.]

Growth and recovery of temporary threshold shift at 4 kHz due to a steady state noise and impulse noises.

7 audiometrically normal, male students were exposed to a steady state noise S of 98 dBA and 2 steady state-impulse combined noises A and B (steady state component of 97 dBA, hammer noise 102 dBA and air exhaustion noise of 118 or 110 dBA) for 40–60 min. The regression line of temporary threshold shift (TTS) growth due to noise A on exposure duration was significantly steeper than that due to noise B. Both the lines were steeper than that due to noise S. The reason of the relatively larger effects of the noises A and B as compared with noise S could be explained by the fact that the noise S did not contain impulse components, because the octave band level at center frequency of 3 kHz of the noise S was roughly equal to that of the steady state noise component of noise A or B. The relatively larger effect of the noise A than B might be attributed mainly to the air exhaustion noise. It was suggested that the effect of a steady state noise on hearing might be additive to that of an impulse noise. The trend relationship between TTS during recovery and recovery time was nearly the same with the 3 noises.

Noise Hazard Meter

A small electronic instrument has been developed to appraise noise exposures in terms of the hazard to human hearing. An analog computer integrates the A-weighted sound level of the noise over the exposure period according to the laws describing growth and recovery of temporary threshold shift [see J. H. Botsford, “Theory of TTS,” J. Acoust. Soc. Amer. 44, 352 (A) (1968)]. The result is a meter reading that indicates the average temporary loss of hearing that the exposure would produce in a group of normal ears. Since this average temporary hearing loss is roughly proportional to the permanent hearing loss that would result from many repetitions of the same exposure, the meter is valuable for appraising noise hazard. All noise exposures that indicate little or no temporary loss are probably safe. The new instrument can be worn by a roving workman and permits evaluation of many exposures to irregular noise that are unassessable by present methods.

Recovery of Noise-Induced Temporary Threshold Shift in Cats

Using a modified conditioning technique of behavioural audiometry, cats were conditioned to respond to pure tones, and their auditory thresholds were determined for pure tones in the range from 125 Hz to 16.000 Hz. The cats were then exposed in groups of three to white noise of various intensities and durations. The temporary threshold shift so induced was measured, and its recovery followed over a period of three months. In this way it has been established that in the cat, as in the human and certain rodents (chinchilla), the recovery of temporary threshold shift follows an exponential course. It is probable that this pattern of recovery is common to all mammals.ResumeAu moyen d'une technique de conditionnement modifiee, des chats ont ete conditionnes a repondre a des frequences pures, et leurs seuils auditifs ont ainsi pu ětre releves de 125 a 16.000 Hz. Les animaux furent ensuite exposes par groupes de trois a un bruit blanc d'intensite et de duree variees. L'elevation temporaire des seuils qui en est ...

継続騒音暴露によるTTSの研究 : (I) 暴露等価法則について

Present paper deals with the problems of predicting temporary threshold shift (TTS) produced by intermittent noises of which off time is longer than two minutes. In the first experiment, to obtain the growth and recovery of TTS at 4 kc, three subjects with normal hearing acuity were exposed to 2000∼4000 cps octaveband noises at 90 db for durations from one minute to 35 minutes. (Figs.2 and 3) In the second experiment, six types of intermittent exposure to 2000∼4000 cpc noises 90 db shown in Fig.4 were used. TTS2 (TTS two minutes after cessation of each exposure), residual TTS (TTS that exists just before the beginning of re-exposure) and TTS in recovery process after the intermittent exposure were measured on the same three subjects. The results of these experiments revealed that 1) the exposure-equivalent rule proposed by Ward etal. was valid in expeirmental conditions containing various off-times from four to 10 minutes, 2) TTS following the intermittent exposure could be predicted based on the exposure-equivalent rule and the equations of recovery process of TTS, and 3) recovery of TTS produced by the repeated exposure proceeded slightly slower than that of TTS produced by the continuous exposure.

TTS<SUB>t</SUB>からTTS<SUB>2</SUB>への変換

Temporary threshold shift (TTS) is characterized by the fact that its magnitude generally decreases with the lapse of time after the end of exposure. To describe the amount of TTS produced by any particular exposure to noise and to provide the uniform reference for this changing magnitude, the value of TTS two minutes after the cessation of exposure (TTS2) is commonly used. In this paper an attempt was made to give the corrections for converting TTSt (TTS measured t minutes after the end of exposure) to TTS2. Ten subjects with normal hearing acuity were exposed to white noise at a level of 105 dB under the following conditions, and TTS were measured 15, 30, 90, 120, 240 and 480 seconds after the end of each exposure. Exposure time Test freq. [table] The amounts of TTS2 at 4 kHz obtained by these exposures were in the range of 0s5 dB, 5s10 dB, 10s20 dB, 20s30 dB and 30s40 dB. The recovery of TTS at 4 kHz proceeded faster at first (during the first 1 or 2 minutes) and slower later. It was also shown that tne rates of recovery of TTS at 1, 2, 4 and 6 kHz were approximately the same when the values of TTS2 were equal. On the basis of recovery data thus obtained, the relation between TTSt and TTS2 were determined graphically with TTS as parameter.

The relation between vitamin A and temporary threshold shift.

The growth and recovery of temporary threshold shift (TTS) produced in 15 male normal-hearing college students by exposure to noise was determined before and after a week of (1) massive doses of vitamin A (100,000 units per day), and (2) a placebo represented to the subjects as another vitamin. Neither vitamin A nor placebo produced any change in the course of the TTS. It is concluded that, as in the case of dark adaptation in vision, an excess of vitamin A has no effect on sensory adaptation, although a lack of vitamin A may retard the adaptation process.

Susceptibility and Sex

Hearing surveys invariably indicate that women have more sensitive hearing than men, the difference increasing with age. This is generally attributed to the fact that women are, on the average, exposed to less noise and gunfire than are men. A possible alternative, however, is that women are less susceptible than men: that in the same noise environment, men will suffer more permanent loss than women. If this were so, one might expect the same to be true of temporary threshold shift (TTS). Therefore the effects of one hour of exposure to 100‐db 1200‐24OO‐cps noise were determined for two groups of normal‐hearing college students: 15 men and 15 women. There were no significant differences, either in growth or recovery of TTS at 3 and 4 kc, between the groups. These results strengthen the hypothesis that differential exposure, rather than differential susceptibility, is responsible for the observed differences in auditory sensitivity between men and women. (Research supported by research grant B‐1122 from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)

Susceptibility and Sex

Hearing surveys invariably indicate that women have more sensitive hearing than men, the difference increasing with age. This is generally attributed to the fact that women are, on the average, exposed to less noise and gunfire than are men. A possible alternative, however, is that women are less susceptible than men: that in the same noise environment, men will suffer more permanent loss than women. If this were so, one might expect the same to be true of temporary threshold shift (TTS). Therefore the effects of one hour of exposure to 100-db 1200-24OO-cps noise were determined for two groups of normal-hearing college students: 15 men and 15 women. There were no significant differences, either in growth or recovery of TTS at 3 and 4 kc, between the groups. These results strengthen the hypothesis that differential exposure, rather than differential susceptibility, is responsible for the observed differences in auditory sensitivity between men and women. (Research supported by research grant B-1122 from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)