This document discusses pure tone audiometry, which is used to measure hearing sensitivity. It describes how sound is a pressure wave that travels through air and is detected by the ear. Pure tone audiometry tests hearing thresholds using pure tones of varying frequency and intensity delivered through air conduction or bone conduction. It outlines the ranges of normal hearing and different types and degrees of hearing loss. Clinical masking is also discussed to avoid inaccurate test results from sound traveling between the ears.

2. Dr Prasanna Datta
Senior Resident
DEPARTMENT OF OTORHINOLARYGOLOGY

3. PURE TONE AUDIOMETRY

4. AUDIOLOGY
The study of sound and hearing
Sound=physical stimulus that evoke
sensation of hearing.
Audiometry=the measurement of
hearing sensitivity.

5. MECHANICAL ELECTRICAL/SENSORY

6. EXTERNAL & MIDDLE EAR - MECHANICAL

7. INNER EAR
COCHLEA, SEMICIRCULAR CANALS AND VESTIBULOCOCHLEAR NERVES -
ELECTRICAL/SENSORY

8. SOUND
Sound is a form of vibration
Vibration is the to-and-fro motion of an
object (guitar string, vocal folds, diaphragm
on an earphone or loudspeaker, tuning
fork)

9. For sound to occur, must have a
SOURCE: Something has to be
disturbed.
FORCE: Something has to disturb it.
MEDIUM (e.g. air): Something has to
carry the disturbances.
SOUND

10. When air molecules are displaced,
pressure waves occur

11. SOUND: PRESSURE WAVE

12. FREQUENCY: The number of cycles that occur in one second.

13. FREQUENCY
Hertz (Hz): Unit of measurement
of frequency
Pitch: Psychological percept of
frequency.
100 cycles per second = 100 Hz
e.g., low frequency sounds = low pitch

14. Frequency Range of Hearing Sensitivity
Humans: 20 Hz to 20 kHz.
– Below 20 Hz, we feel a vibration rather than
hear a sound.
– Most people have very diminished sensitivity
for frequencies > 8000-10, 000 Hz.
Bats (auditory specialists) : 2 kHz-100 kHz.

15. The Minimal Audible Pressure Curve (dB SPL)
Indicates the
minimum average
sound pressure
levels by frequency
for a group of
people with normal
hearing

16. AMPLITUDE/INTENSITY
Decibel (dB): Unit of amplitude
used most frequently in clinical
audiology.
Loudness: The psychological
correlate of amplitude (measured in
sones, phons).

17. Pure Tone Audiometry
• Most common test
• Threshold of audibility
• Activation of auditory
system
• Energy formatted into
neural code
• Air conduction assesses
entire system
• Bone conduction assesses
cochlea onwards

18. Pure Tones
• Auditory acuity
• Spectrally specific
• High frequency tones
stimulate basal turn of
the cochlea
• Low frequency tones
stimulate apical turn
of the cochlea

19. PURE TONE AUDIOMETER

20. SOUND TREATED BOOTH

21. Ranges of Hearing Loss
 -10 – 25 dB HL = Normal range
 26 – 40 dB HL = Mild hearing loss
 41 – 55 dB HL = Moderate

 56 – 70 dB HL = Moderately Severe
 71 – 90 dB HL= Severe
 Greater than 90 dB HL = Profound

22. Normal Hearing

24. Conductive Hearing Loss

25. INNER EAR
COCHLEA, SEMICIRCULAR CANALS AND VESTIBULOCOCHLEAR NERVES -
ELECTRICAL/SENSORY

26. Sensorineural Hearing Loss

27. Mixed Hearing Loss

28. Clinical Masking
• Non-test ear can influence thresholds of the
test ear
• Inter-aural attenuation varies from 40 to 80 dB
with air conduction
• Non-test ear is masked by employing narrow-
band noise to avoid getting a shadow curve
• Inter-aural attenuation is about 0 dB with
bone conduction, hence masking is essential
in all bone conduction studies

29. USES OF PURE TONE AUDIOGRAM
• A measure of threshold by air & bone
conduction & thus the degree & type of
hearing loss.
• A record for future reference.
• Essential for prescription of hearing aid.
• Helps to find degree of handicap for medico-
legal purposes.
• Helps to predict speech reception threshold.