Which frequencies damage hearing

The ear is able to process high-frequency sounds through tiny hair cells in the lower part of the cochlea. These hairs absorb and translate noises into electrical impulses which are sent to your brain, which then interprets the impulses as sound.

If the sensory cells in your cochlea are damaged, you lose the ability to hear and ultimately process these sounds. As the hair cells that perceive low-frequency sounds are located near the top of the cochlea, hearing loss typically occurs at higher frequencies first. The most effective treatment for high frequency hearing loss is hearing aid therapy. A hearing aid has the ability to amplify the high-pitched sounds that the wearer has difficulty perceiving, allowing him or her to understand speech noises more effectively.

Some hearing aids even offer different settings for conversations and directional microphones, allowing the wearer to move effortlessly between talking in groups, on the phone, or one-on-one.

There are many easy and inexpensive things people can do to reduce the likelihood of hearing loss at any age. One of the best ways to prevent hearing damage is to use hearing protection such as ear plugs or approved over-the-ear protection whenever they are exposed to noises over 85 decibels dB. Any excessively noisy activities have the ability to damage hearing, including the use of power tools, riding a motorcycle, shooting firearms, or attending concerts and sporting events.

In addition, you can protect your hearing by keeping the volume turned down on televisions, stereos, and personal electronic devices. It can affect anyone of any age, but is common in older adults with age-related hearing loss, as well as people exposed to loud noises. When listening to people speak, you may struggle to hear certain consonants such as s , h or f , which are spoken at a higher pitch. As a result, speech may sound muffled, especially when you're using the telephone, watching television, or in noisy situations.

People with this type of hearing loss often say they feel like they can hear, but not understand. You also may find it harder to hear women's and children's voices, as well as the sound of birds singing or devices beeping. Diagnosis of high-frequency hearing loss is made after a hearing test in a sound-treated booth at a hearing clinic. A hearing instrument specialist or audiologist usually will conduct the test. The results are plotted on an audiogram.

If a person has high-frequency hearing loss, the audiogram will show a slope to the right, indicating a person has trouble hearing frequencies between 2, and 8, Hz. A person may have mild, moderate, moderately severe, severe or profound hearing loss.

See degrees of hearing loss to learn hearing loss severity is measured. In the example below, the person has moderately severe high-frequency hearing loss that is slightly worse in the right ear.

High-frequency hearing loss occurs when the tiny hair-like sensory hearing cells in your cochlea inner ear are damaged. These hair cells, known as stereocilia, are responsible for translating the sounds your ears collect into electrical impulses, which your brain eventually interprets as recognizable sound.

People of all ages can be affected by high-frequency hearing loss—and the reasons causing it are just as varied. Age-related hearing loss is called presbycusis.

One of the first signs is difficulty understanding speech in noisy environments. Millions of Americans have hearing damage due to noise-induced hearing loss. The damage can occur as the result of a one-time, loud exposure to noise, such as a gunshot or explosion, or can occur over time with constant exposure to noise louder than 85 decibels. Check your family history.

If your relatives developed high-frequency hearing loss, you may be genetically predisposed to developing it as well. Some types of drugs are ototoxic, meaning they are harmful to your hearing health. Some of the more common ototoxic drugs include salicylates aspirin in large quantities, drugs used in chemotherapy treatments and aminoglycoside antibiotics. In severe cases, though, it typically causes low-frequency hearing loss.

High-frequency hearing loss is usually irreversible. Fortunately, though, hearing aids work quite well for this type of hearing loss, and are programmable for hobbies like birding and music. This style has an open fit so it doesn't muffle the low-frequency sounds that you still hear naturally. Scripts written in M atlab 7. No artefacts exceeding the noise floor of the system could be detected. A probe-fit-check procedure preceded and concluded each measurement by presenting a band-stop noise consisting of a low- and a high-frequency band and analysing the ear response using a Fourier transform FT analysis.

If the probe-fit-check procedure at the end of a trial indicated that the probe position had changed, the trial was rejected and repeated. The level of the LF stimulus was monitored continuously during presentation.

All analyses, statistics and visualizations were carried out with scripts written in M atlab 7. For each subject and ear, at least one control experiment without LF stimulation was conducted.

Spectral averaging was applied to each segment to extract the frequency and level of SOAEs. SOAEs within a frequency range of 0.

The power of the noise floor was calculated by averaging the magnitudes in two frequency bands eight spectral lines wide, respectively surrounding the SOAE candidate, each with a 10 Hz spacing from the SOAE candidate frequency.

The level and frequency of SOAEs classified as valid were then analysed over the full recording length. Values from noisy segments or where the signal-to-noise-ratio was too low as assessed by the F -test, see above were rejected. A change-detection algorithm [ 15 ] was employed to test whether the observed level and frequency changes of the SOAE timeseries were randomly occurring.

For this, the cumulative sum of the SOAE level data points from which the mean of the full timeseries was subtracted, was calculated. Then, the difference between the maximum and the minimum of the cumulative sum timeseries was calculated. A bootstrap analysis samples was used to randomly reorder the SOAE timeseries, and the analysis described before was repeated for each of the reordered samples.

The confidence level was then determined by calculating the percentage of bootstrap samples where the difference between the maximum and minimum of the bootstrapped cumulative timeseries was smaller than in the original timeseries.

The descriptive statistics for all analysed parameters are given as median first quartile, third quartile , respectively. The SOAE sound levels recorded in the control condition was 0. This increase was followed by a decrease of both level and frequency relative to pre-exposure figure 1 , left column. In 10 of the 80 pre-existing SOAEs from four subjects, we observed an inverted pattern with initial level and frequency decrease with minima about 1 min after the LF exposure, followed by a level and frequency increase after LF sound stimulation.

Frequency changes can also be expressed logarithmically as fraction of an octave, where Cent equal a semitone, so Cent correspond to an octave, and amounted to 5 Cent 4, 9 Cent with peak values of 25 Cent. Relative to the SOAE frequency in the control condition, the frequency showed initial maximum increases of 4 Cent 3, 7 Cent , followed by maximum decreases of 1 Cent 1, 2 Cent.

Maximum SOAE enhancements amounted to 3. Left column: representative pre- and post LF sound exposure examples of pre-existing SOAE level and frequency changes as a function of time from four different subjects. Representative examples of the fits bold lines to the normalized changes thin line, re.

Interestingly, the sign and magnitude of the level- and frequency oscillations of the permanent and bouncing SOAEs were positively correlated, i. Bouncing SOAEs with negative correlations, i. Further, the magnitude of both the level and frequency changes depended on the SOAE frequency itself: the lower the SOAE frequency, the stronger were both the level- figure 3 b and frequency changes figure 3 c. Correlation between the pre-exposure frequency of bouncing, pre-existing SOAEs and b level and c frequency changes post-exposure, p -values for testing the hypothesis of no correlation against the alternative that there is a non-zero correlation were all smaller than 0.

Only four pre-existing SOAEs from four ears of three subjects emerged after the LF exposure with the same, pre-exposure level and frequency figure 4 a. Their pre-exposure level was however close to our detection threshold and the post-exposure measurement just failed to reach our rigid significance criterion see Methods.

In addition, in a few cases, pre-existing SOAEs were temporarily suppressed by new, neighbouring SOAEs see below for a full description of this class and thus escaped our detection and classification algorithms during that period. Frequency distribution of pre-existing and new SOAEs. Most interestingly, 17 of the 21 subjects revealed an overall of 56 new SOAEs, which had not been measurable before LF stimulation figure 1 , right column for representative examples.

Comparable to the enhancing half cycle of permanent, bouncing SOAEs, their level and frequency oscillated before they disappeared into the noise floor. The duration of the level and frequency changes was New SOAEs started to arise within The time course of level and frequency changes was almost identical and maximum level and frequency changes coincided.

This is not surprising as the LF sound-induced SOAE frequency changes rarely exceeded 30 Hz and therefore do not affect the overall frequency distribution dramatically. The current data show that in humans, active cochlear mechanics, as assessed by SOAE measurements, are significantly affected by LF stimulation.

The level and duration of the LF stimulation employed in this study were well below the current limits satisfying national occupational health regulations. LF-induced changes of cochlear mechanics have also been observed with evoked otoacoustic emissions: Drexl et al. To the best of our knowledge, this is the first comprehensive study focusing on the effect of LF sound on level and frequency of human SOAEs. The time course as well as level and frequency changes of the two SOAEs reported by Kemp [ 13 ] were similar to our data.

The level and frequency of SOAEs can be influenced by several manipulations. Efferent activity, elicited by the presentation of broadband noise at moderate levels to the contralateral ear, causes frequency increases and accompanying level decreases of SOAEs [ 19 , 20 ]. Impedance changes can be elicited by manipulations of the middle ear pressure [ 21 — 23 ], by postural changes [ 24 , 25 ] or by voluntary [ 26 ] or induced [ 19 ] contractions of the middle ear muscles.

Occasionally, the opposite, i. In this study, however, we very consistently observed concomitant changes of frequency and level with the same sign. In addition, the consequences of the manipulations mentioned above typically outlast the stimulation at most by only a few seconds, whereas the SOAE changes we observed can be detected for more than s after the end of LF stimulation.

Exposure to loud broadband noise [ 28 ] or high doses of salicylate [ 29 ] often suppresses SOAEs below the noise floor or causes a prominent reduction in level, accompanied by a frequency decrease.

Norton et al. Their main finding was a pronounced SOAE-level suppression occurring directly after the offset of the intense stimulation, often with a simultaneous frequency decrease.

While the time course of these changes is similar to what we observed, Norton et al. In summary, it is important to note that only exposure to loud broadband noise and high doses of salicylate, both known to cause auditory thresholds shifts [ 28 , 31 ], have led to positively correlated changes of SOAE levels and frequencies. Activation of the efferent system, the middle ear reflex, head position changes and middle ear pressure changes exclusively cause negatively correlated changes of SOAE frequency and level and are not known to induce threshold shifts.

Different models have been proposed to explain the generation of SOAEs. The local-oscillator theory LOT [ 12 , 32 ] is based on the hypothesis that a self-regulation mechanism balances the viscous damping in the cochlea with electromechanical feedback from the cochlear amplifier. It states that SOAEs arise from multiple internal reflections of travelling wave energy that produce a stable standing wave between the cochlear boundary and the peak region of a travelling wave.

A variant of the GST, the active GST [ 11 , 34 , 36 — 39 ] assumes an active amplification process within the cochlea which stabilizes the amplitudes of the standing waves. The many new SOAEs seen after the current LF sound exposure can be interpreted as some of these dropouts becoming temporarily detectable.

These new SOAEs can be the result of altered cochlear reflection and re-emission related to the gain of the cochlear amplifier in the GST. The fact that new SOAEs preferentially appeared in the distribution minimum of permanent SOAE could indicate that dropouts mainly occur in the corresponding, intermediate frequency range.

These changes are not confined to a point location but rather affect an extended region of the cochlea which is why, during the same period, new SOAEs can arise and existing SOAEs can increase in level. Because the SOAEs according to the GST are standing waves, their frequency is determined by the round trip delay and a delay change will consequently cause a frequency shift.

Such a delay change can occur when the stiffness of the OHC is altered. Stiffer OHCs with higher mechanical impedances will cause an increased reflection and re-emission, paired with a phase lead, ultimately causing SOAEs with larger levels and higher frequencies. Thus, the observed positive correlation of level- and frequency changes can be explained in the GST model.

Positively correlated SOAE changes can also be interpreted within the characteristics of the LOT: positively correlated decreases of SOAE level and frequency after traumatic noise were successfully modelled in a nonlinear transmission line model where a decrease in gain of the cochlear amplifier resulted in decreasing SOAE levels and frequencies [ 28 ].

Thus, according to this model, decreased cochlear amplification should result in decreasing SOAE frequencies and level, and, consequently, increased gain of the cochlear amplifier might result in increased SOAE level and frequency. Nonlinear stiffness oscillators show a dependency of the oscillation frequency on the oscillation magnitude [ 40 ]. Accordingly, a change of cochlear gain could result in changed SOAE levels and frequencies, as observed in this study.