Pure tone audiometry in diagnosing hearing
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Pure tone audiometry in diagnosing hearing
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[post_date] => 2025-01-09 08:27:17
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
The most prevalent type of hearing loss, sensorineural, is attributed to damage to the cochlea or the auditory nerve and cannot consequently be corrected through surgical or medicinal means. Causes for this permanent and irreversible hearing loss include physical trauma, viral infection, exposure to loud noises, and aging. On the other hand, conductive hearing loss occurs when there is impairment in the conduction of sound through the middle into the inner ear due to fluid blockage or wax buildup. The distinction can be made by using a tuning fork and placing it behind the ear on the bone to determine whether sound can be heard via bone conduction.
In clinical settings, pure tone audiometry (PTA) is one of the diagnostic tests used to assess the degree and extent of hearing loss by identifying the hearing threshold levels at various frequencies. In a controlled environment, the patient is allowed to increase the decibel level until the provided calibrated tones are heard through the headphones with each ear tested separately.
Figure 1. Audiogram of the left ear of 4 different patients
The audiogram displaying the results is normalized to the hearing curve so that the horizontal line at 0 dB represents normal hearing. Sound intensity does not accurately reflect the change in the ear’s sensitivity with different frequencies and sound levels. Loudness is the strength of the ear’s perception of the sound and is expressed in units of phon. The equal-loudness contours in the following chart reveal the ear’s discrimination versus its sensitivity towards certain frequencies.
Figure 2. Equal-Loudness Contours for the Human Ear
Attribution: Lindosland, CC-BY-SA 3.0
[post_title] => Pure tone audiometry in diagnosing hearing
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[question] => Hearing involves the perception of pitch, loudness, and timbre. Even when a bagpipe, violin, and opera singer produce a sound equal in pitch and loudness, a listener can identify each without looking through their difference in the richness or tone quality. Which of the following accounts for this difference?
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[description] => Reason for the Correct Answer:
Our perception of pitch is most directly attributed to frequency. A high frequency sound would have a high pitch, while a low frequency sound low pitch.
In regards to the speed of sound, within a particular medium any wave travels at the same speed, which is 330 m/s for sound traveling air. The speed only changes when the wave moves from one medium to another.
Beat is the interference of two sound waves at slightly different frequencies, which is perceived by the listener as periodic variations in volume. In the question stem, we are told that the instruments are playing a sound equal in pitch, so there would be no beat frequency.
The richness of a sound is most attributed to the sum of different overtones with the fundamental frequency or higher harmonics with the first. The fundamental frequency is the most audible of all the harmonics, and we identify sounds at a particular pitch through the fundamental frequency.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Overtones
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[1] => Array
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[each_answer] => B. Frequency
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[each_answer] => C. Beat frequency
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[3] => Array
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[each_answer] => D. Speed of sound
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Which patient most likely suffers from a condition called otosclerosis, which is characterized by an abnormal bone growth in the middle ear?
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[answer] => 2
[description] => Reason for the Correct Answer:
For conductive hearing loss, sound has trouble moving from the outer ear to the inner ear. Abnormal bone growth in the middle ear would prevent sound conduction from the outer to inner ear, and it would cause conductive hearing loss.
Such a condition would affect hearing at all frequencies, so we are looking for an audiogram that shows hearing loss at all frequencies.
Patient C and D suffers from potentially some sensorineural hearing loss since the audiogram indicates loss of hearing at a specific range of frequencies.
Patient B is most indicative of someone suffering from otosclerosis due to the reduced hearing sensitivity across all frequencies.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Patient A
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[1] => Array
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[each_answer] => B. Patient B
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[each_answer] => C. Patient C
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[3] => Array
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[each_answer] => D. Patient D
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => Based on Figure 2, which of the following statements best characterizes the data?
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[answer] => 1
[description] => Reason for the Correct Answer:
The ear is most sensitive where the phon contour lines dip the lowest along the y axis. That dip is in the 2000-5000 Hz range. For a person to perceive the same loudness at that frequency, it would take the least sound pressure level.
For very soft sounds, the ear most discriminates against the lowermost and uppermost frequencies. For a person to perceive those frequencies at the same loudness level, there is a greater sound pressure level needed.
Sounds outside the audible range are found below the threshold line and above the 100 phon line. Since the audible range starts at 20 Hz and ends at 20,000 Hz, sounds outside the range are found not only at the left and right edge of the graph, but also at the upper and lower edge of the graph.
Humans can hear sounds in the range of 2000-4000 Hz the best since a low sound pressure level corresponds to the perception of the same loudness compared to those in the other ranges.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Humans can hear sounds in the range of 2000-4000 Hz better than in the range of 20,000-40,000 Hz.
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[1] => Array
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[each_answer] => B. For very soft sounds, the ear most discriminates against the middle frequencies.
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[2] => Array
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[each_answer] => C. The ear is most sensitive to the highest and lowest frequencies.
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[each_answer] => D. Sounds outside of the audible range are found on the left and right edges of the graph.
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[question] => The maximum sensitivity of human hearing is due to the resonance of the auditory canal, which can be considered a closed ended pipe. Using the data in Figure 2, what is the length of the auditory canal? (Use 330 m/s for the speed of sound.)
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[answer] => 2
[description] => Reason for the Correct Answer:
For a closed ended pipe, the air at the closed end must be a node, and since air must be able to be reflected back.
The air at the open end must be an anti-node, and the smallest piece of the wave that fits in the pipe is the fundamental frequency. At that frequency, ¼ of the wavelength of the standing wave fits in the pipe.
Identify the frequency at which you have maximum sensitivity by interpreting the semilog graph. There are lines that go from the widest spaced to the narrowest spaced, and the last line after the most narrow space represents 1, whether it be 1, 10, 100, 1000, etc.
The frequency (ƒ) extracted from the data is approximately 3300 Hz. We use the formula v = ƒλ to find the wavelength of the standing wave.
Since ƒ = 3300 Hz and the speed of sound is 330 m/s, the wavelength is then 0.10 m or 10 cm.
For a closed ended pipe, L = ¼λ so L = 10/4 = 2.5 cm, which is the length of the auditory canal.
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[answers] => Array
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[0] => Array
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[each_answer] => A. 3.3 cm
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[1] => Array
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[each_answer] => B. 2.5 cm
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[2] => Array
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[each_answer] => C. 5.0 cm
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[each_answer] => D. 1.7 cm
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[quiz_unique_key] => 2377279144
[question] => Which patient in Figure 1 most likely suffers hearing loss from a genetic disorder?
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[answer] => 4
[description] => Reason for the Correct Answer:
Patient A has no significant hearing loss in decibels, so he or she has normal hearing.
Patient B has an audiogram that indicates hearing loss across all frequencies, and that is characteristic of conductive hearing loss. For confirmation, a clinician would perform a “bone conduction test” where the patient would be able to perceive the sound delivered by bone conduction.
We know from Figure 2 that our ears are most sensitive to the frequencies in the 2000-4000 Hz range. A loud noise would damage the outer hairs in the cochlea corresponding to those frequencies, just as old age would wear them away.
Patient C has the expected dip at those frequencies, and loud noise damage and old age are attributed to sensorineural hearing loss.
Patient D has an audiogram that illustrates hearing loss in the lower frequencies, which does not match with conductive or sensorineural hearing loss, so patient D most likely suffers from a genetic disorder. For instance, Meniere’s disease is an autosomal dominant disorder where the abnormal fluid volume in the inner ear affects hearing loss in the lower frequencies.
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[each_answer] => A. Patient A
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[each_answer] => B. Patient B
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[each_answer] => C. Patient C
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[each_answer] => D. Patient D
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