Pain Thresholds


Overview
Sensations from High Intensity Sound
Pain, Tickle, and Loudness Thresholds
Relevance to Pain Hyperacusis

Overview

Leipzig,  VEB Gisag, arbeitsmedizinische UntersuchungSound for normal individuals ranges from too quiet to too loud but rarely does sound become physically painful. Physical sensations in the ear are not expected until sound intensities reach 130 dB. This threshold was carefully studied over 60 years ago as researchers were probing what they described as the threshold of “feeling”. Beyond this point a tickling sensation would be felt in the ear. As sound intensity was further increased, they would reach a threshold of pain. These studies, although outrageously dangerous from a modern day perspective, provide fascinating insight for those with pain hyperacusis.

Sensations from High Intensity Sound in Normal Ears

One of the more important contributions of these studies is the qualitative description of the “feeling” that arises from high intensity sound in non-hyperacusis ears. These sensations changed according to both intensity and frequency. It is striking how similar these sensations are to those felt by pain hyperacusis patients. Examples of sensations from a review of such studies (Lierle 1937) are listed below,

Below 1kHz Above 1kHz
Tickle (Most common) Pressure
Itch Sharp Ache
Sting Burning in back of ear
Tingling or Numbness like when foot “goes to sleep.” Pushing inside the ear
Drilling, Probing, or Pinching in back of the ear Diving into deep water
Flutter Vertigo
Going under water Nausea

These symptoms might look familiar to some of you. Sensations of tickle, itching, stinging, burning, and ache can all be experienced by someone with pain hyperacusis for sounds of much lower intensities. Sensations of going under water and flutter might be partially attributed to temporary hearing loss but also may be an expression of TTTS symptoms such as aural fullness and tympanic flutter.

Pain, Tickle, and Loudness Thresholds

An extensive study on pain, tickle, and loudness discomfort thresholds of normal and hard-of-hearing individuals was performed by SR Silverman during WWII. The study included a total of 23 individuals with normal hearing and 33 individuals with mild to profound hearing loss. The instruction given during tickle and pain threshold tests is shown below,

Tickle: “You will hear a tone which will get louder and louder. Tell me when you reach the point where you feel a tickling sensation deep in the ear as though a broom straw were tickling it. Be alert only for the tickling sensation. When the tickle point is reached, say ‘tickle’ and I will shut off the tone. We shall then repeat the procedure with another tone. Are you ready?”

Pain: “You will hear a tone which will get louder and louder. Tell me when you reach the point where you feel a sharp pain deep in the ear. Be alert only for the pain sensation. When the pain point is reached, say ‘pain’ and I will shut off the tone. Are you ready?”

After the sequence of tests was completed, the individual would wait 10 minutes and repeat the tests again for a total of 2 hours of test time. These tests were then repeated weekly over the next 6 weeks. While surely unpleasant for the test subjects, this experiment provides a direct look at both pain and tickle thresholds and their relation to loudness discomfort levels over time.

Pain, Tickle, and Loudness Thresholds in Normal Ears

It is interesting to look at how pain, tickle, and loudness discomfort thresholds change over time in this study. Below are the results of maximum speech tolerance over a period of 6 weeks. Keep in mind that the pain thresholds become limited by the maximum output of the test device on the second half of the chart.

PainThresholds

Data from Tolerance for pure tones and speech in normal and defective hearing., Silverman SR

We can learn a few things from this data. First, all three threshold types increase to some degree over time as a result of the testing. Second, the difference between pain, tickle, and loudness discomfort thresholds is reduced over time, with loudness discomfort thresholds being the most flexible to change. Third, the difference between loudness discomfort and pain thresholds can be high in non-hyperacusis ears, between 10-20dB for speech. A similar trend is found in the 1946 pain threshold study of 46 individuals led by Hallowell Davis.

In-Depth: Hard-of-hearing Thresholds, Frequency Dependence

Comparing Thresholds with Hard-of-hearing Individuals

Below is a comparison of the three threshold types between the normal and hard-of-hearing.

  Normal (dB) Hard-of-hearing (dB)
Loudness Discomfort 117 121
Tickle 128.3 129.3
Pain 137.9 135.3

Although the hard-of-hearing have difficulty detecting softer sounds, louder sounds are still perceived as being loud. This effect is referred to as recruitment. It is important to note that conductive hearing loss (loss in the pathway before the inner ear) will result in a shift of pain thresholds. For example, if an individual has 20 dB of conductive hearing loss, pain thresholds are expected to be 20 dB higher. This is quite different from the results above shown for those with sensorineural hearing loss. This rules out the highly sensitive ear drum as the source of pain.

Thresholds vs Frequency

The plot below shows thresholds found in various studies for minimum an maximum hearing levels including various tickle thresholds.

ThresholdofFeeling

Figure from Handbook of Experimental Psychology, S.S. Stevens, 1951, p. 995.

Relevance to Pain Hyperacusis

The similarity between the symptoms of normal hearing individuals exposed to high intensity sound to those with hyperacusis is interesting. First, it at least affirms that a pathway from sound to pain and tickle sensations is not unusual; in fact, it is natural. Second, results from the Silverman study show that even in normal hearing individuals, there is potential for increasing already high pain thresholds. Third, the similarity in symptoms suggests a treatment that eliminates pain of a normal hearing subject exposed to loud sound might apply to those with hyperacusis. As pain hyperacusis may be difficult to reproduce, experiments geared toward reducing natural sound induced pain would be able to use a more reliable model for developing treatments that might also apply to pain hyperacusis.

A slightly different perspective on this topic can be seen by considering the possibility that the auditory pain threshold in normal ears (120dB-135dB) is the triggering of early stages of acoustic shock disorder (ASD). ASD is the collection of symptoms (often including hyperacusis) that develops after traumatizing sound exposure. More details on ASD can be found in the next section.

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References

Davis H et. al. The selection of hearing AIDS. The Laryngoscope. 1946:56:85–115

Lierle D.M, Reger S. Threshold of feeling in the ear in relation to sound pressures. Arch Otolaryngol. 1936:23(6):653-664

Licklider, Handbook of Experimental Psychology, S.S. Stevens, ed., 1951, p. 995.

Silverman SR. Tolerance for pure tones and speech in normal and defective hearing. Ann Otol Rhin Larnygol 1947:56:658-677.