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Human hearing extends in frequency from 20 to 20,000 Hz, and in intensity from 0 dB to 120 dB HL or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to −5 or even −10 dB. Sound is generally uncomfortably loud above 90 dB and 115 dB represents the threshold of pain. The ear does not hear all frequencies equally well: hearing sensitivity peaks around 3000 Hz. There are many qualities of human hearing besides frequency range and intensity that cannot easily be measured quantitatively. However, for many practical purposes, normal hearing is defined by a frequency versus intensity graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies. Because of the cumulative impact of age and exposure to noise and other acoustic insults, 'typical' hearing may not be normal.[25][26]


The initial physiological symptoms of acoustic shock are considered to be a direct consequence of excessive, involuntary middle ear muscle contractions. While the stapedial reflex is an acoustic reflex triggered by high volume levels, the tensor tympani reflex is a startle reflex (6, 7) which is exaggerated by high stress levels. The tensor tympani muscle contracts immediately preceding the sounds produced during self-vocalisation, suggesting it has an established protective function to loud sounds (1), assists in the discrimination of low frequency sounds (8), and is involved in velopharyngeal movements (8).
Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins.[2] A common condition that results in hearing loss is chronic ear infections.[2] Certain infections during pregnancy, such as cytomegalovirus, syphilis and rubella, may also cause hearing loss in the child.[2][10] Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear.[2] Testing for poor hearing is recommended for all newborns.[8] Hearing loss can be categorized as mild (25 to 40 dB), moderate (41 to 55 dB), moderate-severe (56 to 70 dB), severe (71 to 90 dB), or profound (greater than 90 dB).[2] There are three main types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.[3]
Children may be less likely to say they have tinnitus unless they’re questioned about it. It's important that you talk to your child to get an idea of how they are coping and their feelings towards tinnitus. In fact, most children with tinnitus are not bothered by it. If your child does find it upsetting, always be supportive and reassure your child that they are not alone.
Spread of infection. Untreated infections or infections that don't respond well to treatment can spread to nearby tissues. Infection of the mastoid, the bony protrusion behind the ear, is called mastoiditis. This infection can result in damage to the bone and the formation of pus-filled cysts. Rarely, serious middle ear infections spread to other tissues in the skull, including the brain or the membranes surrounding the brain (meningitis).
If your child has not been born with hearing problems, it is most likely that their hearing loss is temporary. However, some children are born deaf. Each year in the UK, around 840 babies are born with permanent hearing loss. Your child will have a hearing test soon after they’re born (the Newborn Hearing Screening Programme ), so any problems with their hearing can be picked up early on.
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An exaggerated startle reflex and hypervigilance are listed as symptoms of PTSD (DSM-IV, D.5), and individuals with PTSD have been shown to produce heightened autonomic responses (eg increased heart rate) to acoustic stimuli that would not be expected to produce a startle response. My clinical observation of over 85 ASD clients shows that once TTTS has become established, auditory hypervigilance and an exaggerated startle reflex can lead to the escalation of hyperacusis, where the range of sounds that elicit this involuntary response increases to include more everyday sounds. These sounds become increasingly intolerable when TTTS symptoms are exacerbated following exposure. Phonophobia, headache, fatigue, anxiety, and depression can result, particularly if an inadequate explanation or diagnosis of TTTS symptoms is not offered.
It is not a disease or illness; it is a symptom generated within the auditory system and usually caused by an underlying condition. The noise may be in one or both ears, or it may feel like it is in the head. It is difficult to pinpoint its exact location. It may be low, medium or high pitched and can be heard as a single noise or as multiple components.
MRI (or magnetic resonance imaging) scan is a radiology technique which uses magnetism, radio waves, and a computer to produce images of body structures. MRI scanning is painless and does not involve X-ray radiation. Patients with heart pacemakers, metal implants, or metal chips or clips in or around the eyes cannot be scanned with MRI because of the effect of the magnet.
Subjective tinnitus is the most frequent type of tinnitus. It may have many possible causes, but most commonly it results from hearing loss. When the tinnitus is caused by disorders of the inner ear or auditory nerve it is called otic (from the Greek word for ear).[23] These otological or neurological conditions include those triggered by infections, drugs, or trauma.[24] A frequent cause is traumatic noise exposure that damages hair cells in the inner ear.
Acoustic qualification of tinnitus will include measurement of several acoustic parameters like frequency in cases of monotone tinnitus or frequency range and bandwidth in cases of narrow band noise tinnitus, loudness in dB above hearing threshold at the indicated frequency, mixing-point, and minimum masking level.[52] In most cases, tinnitus pitch or frequency range is between 5 kHz and 10 kHz,[53] and loudness between 5 and 15 dB above the hearing threshold.[54]
When we hear, sound travels into the ear and then the hearing nerves take the signals to the brain. The brain is then responsible for putting it all together and making sense of the sound. Because the ears don’t know what’s important and what’s not, they send a lot of information to the brain. This is too much information for us to process, so the brain filters out a lot of unnecessary ‘activity’ and background sound, such as clocks ticking or traffic noise.
Some instances of tinnitus are caused by infections or blockages in the ear, and the tinnitus can disappear once the underlying cause is treated. Frequently, however, tinnitus continues after the underlying condition is treated. In such a case, other therapies -- both conventional and alternative -- may bring significant relief by either decreasing or covering up the unwanted sound.
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