Download Keys used during Test - ee.iitb

MICROCONTROLLER BASED AUDIOMETER
IITB-AUD2K1
USER’S MANUAL
Signal Processing and Instrumentation (SPI) Lab
Department of Electrical Engineering
Indian Institute of Technology Bombay
Powai, Mumbai 400 076, India.
Tel. No. (91-022) 2576 4417, E-mail spilab@ee.iitb.ac.in
Website: http://www.ee.iitb.ac.in/~spilab
Prepared by Vineet Aras, (Supervisor: Prof. P. C. Pandey), Nov 2003,
Based on M.Tech. dissertation “A microcontroller based audiometer” by Dipak M. Patel,
EE Dept., IIT Bombay, 2002.
1
TABLE OF CONTENTS
1
2
INTRODUCTION
1.1 General Description
3
1.2 Features and specifications
4
INSTALLATION / PHYSICAL INTERFACE
2.1 Mechanical
5
2.2 Rear-Panel Connections
5
2.3 Front-Panel Keys and Displays
6
1 Front-Panel keys
2 Keys functions
3 Display
3
OPERATING INSTRUCTIONS
3.1 Procedure
8
1 Self Test
8
2 Initialization
8
3 Testing
9
Manual Test
10
Automatic Test
12
Short Increment Sensitivity Index Test
14
Tone Decay Test
16
4 Display and Print
4
17
BRIEF AUDIOMETRY DESCRIPTION
4.1 Pure Tone Audiometry
19
4.2 Tone Decay Test
20
4.3 Short Increment Sensitivity Index Test
20
4.4 Speech Audiometry
20
2
1.
INTRODUCTION
1.1
GENERAL DESCRIPTION
This audiometer incorporating the microcontroller technology improves
reliability, accuracy, flexibility and ease of operation. It was under development at IIT
Bombay since 1997. It is used for carrying out various audiometric tests like Pure
tone audiometry, Speech audiometry, Tone Decay test, Short Increment Sensitivity
Index (SISI) test. These audiometric tests are used to identify and quantitatively
determine the degree of hearing loss of a person by measuring his hearing sensitivity,
so that suitable medical treatment can be provided. It helps in assessing the nature,
degree, and probable cause of the hearing impairment. In this technique, auditory
stimuli are presented to the person who responds to these stimuli. There are different
audiometric procedures depending on the stimuli used. The auditory stimulus is in
form of test tones of different frequency and level that are presented and hearing
thresholds are determined on the basis of patient’s response. The minimum intensity
level of these stimuli to which consistent responses are obtained is taken as the
“threshold of hearing”. Depending on this threshold, the patient’s hearing sensitivity
can be estimated and best-suited medical treatment or hearing aid or other assistive
devices can be prescribed.
This microcontroller based diagnostic audiometer is developed which operates
over full frequency range (250 Hz to 8 kHz) and acoustic output level of 0 to 100 dB
HL. It can also generate warble tone having 10% frequency deviation, and amplitude
modulated tone with ± 5 dB modulation. The instrument provides a
broadband/narrow-band masking noise, with level selection. Appropriate noise level
is selected for masking purpose such that it prevents cross hearing in the non-test ear
due to transmission of sound from test ear through skull bone. Facility of air and bone
conduction is provided. All the controls are through a 4  4 membrane keypad and
indications are using 16 characters  2 lines LCD display. The instrument is menu
driven and has option of manual and automated audiometry. It has RS232 interface
for downloading the test results to a computer. At power on, it carries out a self test of
the output levels.
3
1.2
FEATURES AND SPECIFICATIONS
Audiometer type: dual channel microcontroller based audiometer, with pure/warble
tone/AM tone stimulus and wide-band/narrow-band masking noise. Facility of air and
bone conduction. Facility of Manual, Automatic, SISI test, tone decay test and speech
audiometry.
Circuit size: two double-sided PCBs with PTH. PCB-1 of 14.5 cm  13.5 cm and
PCB-2 of 10 cm  13.5 cm.
Stimulus: crystal controlled test tone frequencies, with intensity level controlled in 5
dB steps. The ranges of tone output for air conduction and bone conduction are 0 to
Lmax(dBHL) for different frequencies as given below
Frequency (Hz)
250 500 1000 1500 2000 3000 4000 6000 8000
Air Lmax (dBHL)
Bone Lmax (dBHL)
90
90
100
100
100
100
100
100
90
80
100
100
100
100
100
100
90
80
Masking noise: broadband/narrow-band noise in 5 dB step. Wide-band noise: flat
spectrum up to 8 kHz, with approx. 12 dB/octave roll off on the higher side. Narrowband noise: centered at test tone frequency, 3-dB BW ≈ 0.55 octave, 20-dB BW ≈ 4
octave.
Output Devices: Headphone type TDH-39 (software calibration for other headphones,
by changing a table). Bone Vibrator type Oticon 70127 (software calibration for
others)
Control and indication: control through 44-matrix keypad of size 99 cm.
16 characters  2 lines LCD display with font 57 or 510 dots.
Operation: software controlled menu driven manual / automated modes.
Result Storage: for one set of the test results with rewrite facility.
Interfacing: serial port (TxD, RxD, and GND), TTL level, baudrate of 2400 bits per
second, 7 bit data, and even parity.
Self test: internal monitoring of output levels.
Size: 305 mm x 220 mm x 50 mm
Power supply: +5V, 20 mA for digital and  5V, 120 mA for analog.
4
2.
INSTALLATION
2.1
MECHANICAL
Dimension – 305 mm x 220 mm x 50 mm
2.2
REAR – PANEL CONNECTIONS
5
2.3
FRONT – PANEL KEYS AND DISPLAYS
(1)
Front panel keys
Stimulus
Type
Noise type


Stimulus
Level




Noise
Level


Stimulus
Duration
Test Mode


Frequency



Tone On
Tone Off
Save
Air / Bone
Display
Ok
Print
(2)
Key functions
Following membrane type keys have been used in this system.
Keys used during Initialization
Tone Type. This key will be used at the time of initialization of tone presentation to
select the tone type. (Pure, Warble, AM, Speech)
Noise Type. This key will be used during the initialization to select the noise type. It
may be wide band (WB), narrow band (NB), or no noise (--).
Tone Dur.. This key is used during initialization to select the duration up to which the
tone will be presented. Four options are available viz. 2 sec, 3 sec, 4 sec, and
continuous.
Test Mode. This key is pressed to select the mode of operation of the audiometer,
(manual, automatic, SISI with 1 dB/3 dB/5 dB bursts, TDT).
Air / Bone. This key decides mode of conduction during test
Ok. This key is used to confirm the message displayed and to proceed further.
6
Keys used during Test
Frequency  Whenever this key is pressed, frequency of tone is increased. Display
shows the next frequency with a level of tone initialized at 30 dB HL.
Frequency  When ever this key is pressed frequency of the tone decreases.
Tone  This key is used to increase tone level in 5 dB steps
Tone  This key is used to decrease tone level in 5 dB steps
Noise  This key is used to increase the level of masking noise in 5 dB steps.
Noise  This key is used to decrease the level of masking noise in 5 dB steps.
Tone on. This key is pressed to present the tone to the subject. It is presented
according to the tone type, duration, and level, which are preselected. When the tone
is on, a message ‘PR’ is displayed at the bottom right corner.
Tone Off. This key is pressed to interrupt the tone before the tone on duration has
lapsed.
Save. This key is used to save the hearing threshold for the selected frequency into the
memory.
Keys used to display and print
Display. This key is used to display the results stored. When this key is pressed all the
threshold values are displayed starting with value corresponding to lowest frequency
at the left corner
Print. This key is pressed to transfer the results to the printer / computer connected to
serial port.
(3) Displays
The display indications are on a 16 characters  2 lines LCD display
7
3.
OPERATING INSTRUCTIONS
The operator friendly software for this audiometer has been designed considering the
simplicity, flexibility and ease of operation. Any of the parameters can be entered or
altered from the front panel keypad.
3.1
Procedure
After making all the required connections and after Power on, the display shows
Audiometer
2002
(1) Self-Test - The unit then performs the self-test (ST) to verify the output levels of
the audiometer, and the display shows
ST
In this test, starting with the lowest frequency i.e. 250 Hz, the test tone level is
increased from 0 dB in steps of 1 dB and this level is compared with a reference
level. The incrementing counter is displayed on the upper left corner. And when
the value reaches the reference level, the value is frozen on the display. The cursor
moves towards right for the next frequency, and the same procedure repeats. At
the end, the values corresponding to all the nine test frequencies are displayed.
50 45 43 42 44 45
44 47 48
Press the “Ok” key on the keypad to proceed further.
Intermidiately the test can be terminated by pressing either the Response switch
or the “Ok” key on keypad.
(2) Initialization – The unit then enters the initialization process and the display
shows
  

Stimulus Noise Stimulus Test
type type duration mode

  
Pure WB 2sec Man
Air LFT
<OK>

Conduction type
(Air/Bone)
Each of the above in the display is one of the options corresponding to the
parameters indicated by the arrows. For a particular parameter, repeated pressing
of its corresponding key changes and displays the options cyclically in the order
given in the table and one of the available options can be selected for that
parameter.
The various Test modes can be selected by pressing the “Test Mode” key. The
following table gives the parameter options available (or displayed) in various test
8
modes. The characters in brackets are the characters that would be indicated on
the display for its respective option.
Table of Parameter options available in different Test modes
Test modes
Parameters
Stimulus duration
2 seconds (2sec)
Stimulus type
Noise type
Pure tone (Pure)
Wide band (WB)
Warble tone (Wrbl)
Narrow band (NB)
A.M. tone (Amtn)
No noise (--)
Manual test (Man)
3 seconds (3sec)
4 seconds (4sec)
Conduction type (Air/Bone)
Air conduction for left ear
(Air LFT)
Air conduction for right ear
Continuous(Cont)
(Air RGT)
Interrupted
(Intr)
Bone conduction (BON)
Air conduction for left ear
Speech (Spch)
Wide band (WB)
No noise (--)
Continuous
(Cont)
Automatic test
(Aut)
Wide band (WB)
Warble tone (Wrbl)
Narrow band (NB)
A.M. tone (Amtn)
No noise (--)
Air conduction for right ear
(Air RGT)
2 seconds (2sec)
Pure tone (Pure)
(Air LFT)
3 seconds (3sec)
4 seconds (4sec)
Bone conduction (BON)
Air conduction for left ear
(Air LFT)
Air conduction for right ear
(Air RGT)
Bone conduction (BON)
SISI test with 1 dB
bursts (SI1)
Air conduction for left ear
SISI test with 3 dB
bursts (SI3)
Wide band (WB)
Pure tone (Pure)
Narrow band (NB)
Continuous
(Cont)
Air conduction for right ear
(Air RGT)
No noise (--)
SISI test with 5 dB
bursts (SI5)
(Air LFT)
Bone conduction (BON)
Air conduction for left ear
Wide band (WB)
Tone Decay Test
(TDT)
Pure tone (Pure)
Narrow band (NB)
No noise (--)
Continuous
(Cont)
(Air LFT)
Air conduction for right ear
(Air RGT)
Bone conduction (BON)
After having selected the Test mode, and the corresponding Parameter options,
using the respective keys, press the “Ok” key to proceed.
(3) Testing – The unit then enters the process of testing. There are various types of
tests (as selected during the initialization process) that can be performed using this
audiometer. We will consider the procedure for each test.
9
3.2 “Manual”: Manual Mode for Tone Audiometry [Pure / Wrable /
A.M. Tones]
If Pure, Warble or AM tone is selected during initialization, after pressing “Ok”
key, the display shows
Test
Stimulus
Test mode selected during
frequency
level (HL) initialization (here Manual)


1000Hz 030dB Man
WB
000dB

Noise type selected during initialization
Noise level
(WB/NB/none)
(i) By pressing the “Frequency ” or “Frequency ” keys, the test frequency can
be increased or decreased so as to set to one of the test frequencies (250Hz,
500Hz, 1000Hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz, 6000Hz, 8000Hz).
(ii) The Stimulus level can be selected by pressing the “Stimulus level ” or
“Stimulus level ” keys.
(iii) If Wide Band or Narrow Band noise has been selected during initialization, the
noise level can be selected by pressing the “Noise level ” or “Noise level ”
keys. Appropriate noise level should be selected for masking purpose such that it
prevents cross hearing in the non-test ear due to transmission of sound from test
ear through skull bone.
(iv) To start the test i.e. to present the stimulus, press the “Tone ON” key. The
display shows
250Hz 030dB Man
WB
020dB PR
“PR” indicates tone present. The stimulus (pure, warble or AM tone depending on
stimulus type selected during initialization) is presented from one side of
headphone and the noise (WB or NB or no noise depending on Noise type
selected during initialization) from the other side of headphone. The subject is
asked to press the response switch when he hears the tone
(v) If the stimulus duration selected during initialization is 2 seconds, 3 seconds or 4
seconds, the tone turns off after that duration. If the response switch is not pressed
within stimulus duration, the display indicates No Response “NR” after the
duration has elapsed.
250Hz 030dB Man
WB
020dB NR
If the stimulus duration selected is ‘Continuous’ a continuous tone is presented. If
the stimulus duration selected is ‘Interrupted’ a tone that alternately turns on and
off is presented.
10
(vi) If the response switch is pressed within the stimulus duration, the tone turns off
and the display indicates Response “RE”.
250Hz 030dB Man
WB
020dB RE
(vii) The tone can be turned off anytime by pressing the “Tone Off” key and the
display shows blank at bottom right corner
250Hz 030dB Man
WB
020dB
(viii) If there is no response, the operator increases the stimulus level. If there is a
response, the operator decreases the level and tone is again presented. In this way
by several presentations the hearing threshold (minimum stimulus level at which
the subject just hears the presented stimulus) is measured for the selected
frequency.
(ix) This threshold level for that frequency can be saved (under the air left / air right /
bone conduction as selected during initialization) by pressing the “Save” key and
the display shows
Reading saved...
after the reading is saved, the display changes to
1000Hz 030dB Man
WB
000dB
(x) Repeat the procedure for other required test frequencies and save the threshold
levels corresponding to those frequencies.
(xi) Press any one of the keys (Stimulus type, Noise type, Stimulus duration,
Conduction Air/Bone type) to come out of test process. The display shows
Pure WB 2sec Man
Air LFT
<OK>
The display will show the options that were selected before getting in the testing
process.
(xii) If required, change the Conduction type to Air Right or Bone and repeat steps
from (i) to (xi). We can proceed to the “Display” and “Print” process, given later.
3.3 “Manual”: Manual Mode for Speech Audiometry
The stimulus type can be selected as Speech, which is generally required for
Speech Audiometry in which the subject is asked to identify words presented to
him. After selecting Speech as stimulus type and pressing “Ok” in the
initialization process, the display shows
Speech 030dB Man
WB
000dB
11
Follow the procedure of Manual test for Pure/Warble/AM Tone from steps (ii) to
(xii).
Note that in
step (iii) masking noise, only Wide Band noise or No noise is possible
step (iv) there is a bar display to indicate input speech signal level
step (v) the stimulus duration is always continuous so that speech stimulus is
present.
step (x) is skipped
3.4 “Automatic”: Automated Mode for Tone Audiometry [Pure /
Warble / AM Tones]
After selecting Automatic test as test mode and pressing “Ok” in the initialization
process, the display shows
Test
Stimulus
Test mode selected during
frequency
level (HL) initialization (here Automatic)


1000Hz 030dB
WB
000dB
Aut

Noise type selected during initialization
Noise level
(WB/NB/none)
(i) By pressing the “Frequency ” or “Frequency ” keys, the test frequency can
be increased or decreased so as to set to one of the test frequencies (250Hz,
500Hz, 1000Hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz, 6000Hz, 8000Hz).
(ii) The Stimulus level is selected by pressing the “Stimulus level ” or “Stimulus
level ” keys.
(iii) If Wide Band or Narrow Band noise has been selected during initialization, the
noise level can be selected by pressing the “Noise level ” or “Noise level ”
keys. Appropriate noise level is selected for masking purpose such that it prevents
cross hearing in the non-test ear due to transmission of sound from test ear
through skull bone.
(iv) To start the test i.e. to present the stimulus, press the “Tone ON” key. The
display shows
250Hz 030dB Aut
WB
020dB PR
“PR” indicates tone present. The stimulus (pure, warble or AM tone depending on
stimulus type selected during initialization) is presented from one side of
headphone and the noise (WB or NB or no noise depending on noise type selected
during initialization) from the other side of headphone. The subject is asked to
press the response switch when he hears the tone
(v) If the stimulus duration selected during initialization is 2 seconds, 3 seconds or 4
seconds, the tone turns off after that duration. If the response switch is not pressed
12
within this stimulus duration, the display indicates No Response “NR” after the
duration has elapsed.
250Hz 030dB Aut
WB
020dB NR
Since no response, the stimulus level is automatically increased, the tone is
presented again for the set duration and the display shows
250Hz 040dB Aut
WB
020dB PR
(vi) If the response switch is pressed within the stimulus duration, the tone turns off
and the display indicates Response “RE”
250Hz 040dB Aut
WB
020dB RE
Since response is present, the stimulus level is automatically decreased, the tone is
presented again for the set duration and the display shows
250Hz 035dB Aut
WB
020dB PR
(vii) In this way, if there is no response, the system automatically increases the
stimulus level. If there is a response, the system automatically decreases the level
and the tone is presented again. Thus by several presentations the hearing
threshold (minimum stimulus level at which the subject responds 50% times) is
tracked and obtained automatically for the selected frequency.
(viii) This threshold level for that frequency is automatically saved (under the air left /
air right / bone conduction as selected during initialization) and the display shows
Reading saved...
after the reading is saved, the display changes back to
250Hz 030dB Aut
WB
020dB
Note that, while the test is in process i.e. before the threshold is measured and
saved, it can be discontinued by pressing the “Tone Off” key. In this case, the
display shows blank at bottom right corner
(ix) Repeat the procedure for other required test frequencies to automatically save the
threshold levels corresponding to those frequencies.
(x) Press any one of the keys (Stimulus type, Noise type, Stimulus duration,
Conduction Air/Bone type) to come out of test process. The display shows
Pure WB 2sec Aut
Air LFT
<OK>
The display will show the options that were selected before getting in the testing
process.
(xi) If required, change the Conduction type to Air Right or Bone and repeat steps
from (i) to (x). We can proceed to the “Display” and “Print” process, given later.
13
3.5 SISI test with 1 dB / 3dB / 5 dB bursts
After selecting the Short Increment Sensitivity Index (SISI) test with 1 dB / 3dB /
5 dB bursts as Test mode and pressing “Ok” in the initialization process, the
display shows
Test mode (SI1 - with 1 dB increment,
Test
Stimulus
SI3 - with 3 dB increment,
Frequency
level (HL)
SI5 – with 5 dB increment)

1000Hz 030dB
WB
000dB
SI1

Noise type selected during initialization
Noise level
(WB/NB/none)
(i) By pressing the “Frequency ” or “Frequency ” keys, the test frequency can
be increased or decreased so as to set to one of the test frequencies (250Hz,
500Hz, 1000Hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz, 6000Hz, 8000Hz).
(ii) The Stimulus level is selected by pressing the “Stimulus level ” or “Stimulus
level ” keys.
(iii) If Wide Band or Narrow Band noise has been selected during initialization, the
noise level can be selected by pressing the “Noise level ” or “Noise level ”
keys. Appropriate noise level is selected for masking purpose such that it prevents
cross hearing in the non-test ear due to transmission of sound from test ear
through skull bone.
(iv) To start the test i.e. to present the stimulus, press the “Tone ON” key. The
display shows
1000Hz 035dB SI1
WB
020dB PR
“PR” indicates tone present. The tone is presented from one side of headphone
and the noise (WB or NB or no noise depending on noise type selected during
initialization) from the other side of headphone.
The tone is presented as 20 bursts of 1 dB / 3 dB / 5 dB increment above the
selected stimulus level for 300 ms at every 5 seconds. Out of the 300 ms burst,
rise time and fall time are 50 ms each. The patient is asked to press the response
button whenever he detects a change in the level.
(v) Since the stimulus duration is ‘Continuous’, the tone is presented as described in
(iv) till 20 bursts are completed. When the first burst arrives, it is indicated by 01
at the bottom right corner of the display.
1000Hz 035dB
WB
020dB
14
SI1
01
If the response switch is pressed within 5 secs duration, the display indicates
Response “RE”
1000Hz 035dB SI1
WB
020dB RE
then the second burst is presented, indicated by 02 on the display
1000Hz 035dB
WB
020dB
SI1
02
If the response switch is not pressed within 5 secs duration, the third burst is
presented, indicated by
1000Hz 035dB
WB
020dB
SI1
03
(vi) This process continues till 20 bursts are presented i.e. whenever there is no
response, the next bursts is presented indicated by an increment in the number
at the right bottom of display, and whenever there is a response it is indicated
by a response ‘RE’ is automatically counted by the system. Then the next
burst is presented, and it is indicated by an increment in the number at the
right bottom of display.
(vii) After the twentieth burst, the number of bursts out of 20 the patient is able to
detect is saved (under the air left / air right / bone conduction as selected during
initialization) and displayed as percentage for that particular frequency.
Reading saved...
after some time…
Result
035%
Note that, intermediately, while the test is in process i.e. before saving, it can be
discontinued anytime by pressing the “Tone Off” key and the display shows
blank at bottom right corner
(viii) Repeat the procedure for other required test frequencies and save the percent
values corresponding to those frequencies.
(ix) Press any one of the keys (Stimulus type, Noise type, Stimulus duration,
Conduction Air/Bone type) to come out of test process. The display shows
Pure WB Cont
Air LFT
SI1
<OK>
The display will show the options that were selected before getting in the testing
process.
(x) If required, change the Conduction type to Air Right or Bone and repeat steps
from (i) to (ix). We can proceed to the “Display” and “Print” process, given later.
15
3.6 Tone Decay Test
After selecting Tone Decay Test (TDT) as Test mode and pressing “Ok” in the
initialization process, the display shows
Test
Stimulus
Test mode selected during
frequency level (HL) initialization (here Tone Decay Test)

1000Hz 030dB
WB
000dB
TDT

Noise type selected during initialization
Noise level
(WB/NB/none)
(i) By pressing the “Frequency ” or “Frequency ” keys, the test frequency can
be increased or decreased so as to set to one of the test frequencies (250Hz,
500Hz, 1000Hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz, 6000Hz, 8000Hz).
(ii) The Stimulus level can be selected by pressing the “Stimulus level ” or
“Stimulus level ” keys.
(iii) If Wide Band or Narrow Band noise has been selected during initialization, the
noise level can be selected by pressing the “Noise level ” or “Noise level ”
keys. Appropriate noise level is selected for masking purpose such that it prevents
cross hearing in the non-test ear due to transmission of sound from test ear
through skull bone.
(iv) To start the test i.e. to present the stimulus, press the “Tone ON” key. The
display shows
1000Hz 030dB TDT
WB
020dB PR
“PR” indicates tone present. The pure tone is presented from one side of
headphone and the noise (WB or NB or no noise depending on noise type selected
during initialization) from the other side of headphone. The subject is asked to
press the response switch when he does not hear the tone.
(v) Since the stimulus duration is continuous, the tone is continuously presented.
(vi) Whenever the response switch is pressed the display indicates Response “RE”
1000Hz 030dB TDT
WB
020dB RE
after sometime
1000Hz 030dB TDT
WB
020dB NR
indicating that the subject is not able to hear the tone. The time for which the
subject was able to hear the tone is measured.
16
(vii) If the subject is able to hear the tone for more than 1 minute, the operator
decreases the stimulus level. If the subject is able to hear the tone for less than 1
minute, the operator increases the level and tone is again presented. In this way by
several presentations the hearing threshold (minimum stimulus level at which the
subject is able to hear the tone for about 1 minute) is tracked and obtained for the
selected frequency.
(viii) This threshold level for that frequency can be saved (under the air left / air right
/ bone conduction as selected during initialization) by pressing the “Save” key
and the display shows
Reading saved...
after the reading is saved, the display changes to
1000Hz 030dB TDT
WB
000dB
Note that, intermediately, while the tone is being presented, it can be turned off
anytime by pressing the “Tone Off” key and the display shows blank at bottom
right corner
(ix) Repeat the procedure for the other required test frequencies and save the
threshold levels corresponding to those frequencies.
(x) Press any one of the keys (Stimulus type, Noise type, Stimulus duration,
Conduction Air/Bone type) to come out of test process. The display shows
Pure WB Cont TDT
Air LFT
<OK>
The display will show the options that were selected before getting in the testing
process.
(xi) If required, change the Conduction type to Air Right or Bone and repeat steps
from (i) to (x). We can proceed to the “Display” and “Print” process.
3.7 Display and Print
After any test, the values saved during the test under Air Left, Air Right and Bone
conduction can be viewed by using this facility. After coming out of the test
process, the display shows
Pure WB 2sec Man
Air LFT
<OK>
The display will show the options that were selected before getting in the testing
process.
(i) Press the “Display” key, the display shows
Freq LFT RGT BON
250 015 020 030
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Here the display shows for a particular frequency, the values stored during any
recent test (i.e. threshold levels for Manual, Automatic, TDT tests and percentage
values for SISI test) under Air Left, Air Right and Bone conduction
(ii) By pressing the “Frequency ” or “Frequency ” keys, the test frequency can
be increased or decreased so as to view one of the test frequencies (250Hz, 500Hz,
1000Hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz, 6000Hz, 8000Hz) and its
corresponding values.
(iii) Press “Ok” to come out of Display process.
Pure WB 2sec Man
Air LFT
<OK>
(iv) Press “Print” key, the display shows
Print Results ?
(v) Press “OK” to print, display shows
Printing...
After some time
Pure WB 2sec Man
Air LFT
<OK>
(vi) The next test or session can be performed.
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4
BRIEF AUDIOMETRY DESCRIPTION
Audiometry is the technique to identify and quantitatively determine the
degree of hearing loss of a person by measuring his hearing sensitivity, so that
suitable medical treatment or one of the appropriate hearing aids and assistive devices
can be prescribed. An audiometer is an instrument, which is used for carrying out the
audiometric tests. An audiogram, is a plot of hearing thresholds for standard test tone
frequencies (250 to 8k Hz). Minimum intensity of the stimulus at which patient is able
to hear is called the threshold of hearing. 0dB HL corresponds to hearing threshold of
a normal person.
Each section of the ear has diseases specific to it and specific tests
(investigations) are there to identify disorders in each portion. The common causes of
disorder in the external auditory meatus is collection of wax, fungal debris, or foreign
body in it. The middle ear comprises of the eardrum, the ossicles, and the air space
within the cavity of the middle ear. The common diseases affecting this portion are
perforation in the ear drum, a stiffness or damage to the chain of small bones in the
ear, and collection of fluid in the middle ear space. Any deafness due to a disorders in
the external auditory meatus or in the middle ear is called conductive deafness.
Disorders of the inner ear, comprising of the cochlea and the auditory nerve going to
the brain, cause a deafness called sensorineural (perceptive) deafness. Deafness due to
disorder of the nerve is called retrocochlear deafness and deafness due to disorders of
the nerves which carry the sensation of hearing still higher up to auditory cortex are
called central deafness. When sound reaches the inner ear through the eardrum, this
phenomenon is called air conduction. Sound, particularly in the low frequency range,
may reach the inner ear via the bones in the head rather than from the eardrum, this
phenomenon being called bone conduction
Risk of getting the non-test ear stimulated due to sound in test ear transmitted
through skull bone is called cross hearing and can be prevented by providing masking
noise is the non-test ear. There are two types of masking noise, namely Wide band
noise that range from 250 to 8k Hz and Narrow band noise that is centered at tone
frequency and gives same masking effect as wide band noise at a lower level.
4.1 Pure Tone Audiometry
This test tells whether the deafness is conductive (disorder in external auditory
meatus and / or middle ear) or sensorineural (disorder in the inner ear or in the nerve
of hearing in the brain) or mixed.
Initially a pure tone of 30 dB HL is presented to the subject. If the response is
positive, the tone level is decreased in steps of 10 dB till the patient does not give
response. On the other hand, if the patient does not hear it, the level is raised in steps
of 10 dB step until it is heard. If the patient hears this tone, the tone is again decreased
by 5 dB. If the patient does not hear it, the tone is again raised by 5 dB. In this way by
several presentations, the hearing threshold is obtained for various test
frequencies.Different shapes of audiograms are associated with different types of
hearing loss. The difference between air conduction and bone conduction thresholds
at a given frequency reflects conductive hearing loss. The difference between bone
conduction thresholds and 0 dB reflects sensorineural loss.
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4.2
Tone Decay Test
If Pure tone Audiometry test has diagnosed the deafness to be sensorineural in
type, there are some specialised test like- SISI, Tone Decay, Speech Audiometry tests.
Tone Decay Test (TDT) is the most commonly used.
In TDT, for a freq., the tone is presented and the level is incremented, starting
form 30 dB HL, until the subject responds. If the subject is able to hear the tone for
more than one-minute, the tone level is decremented in steps of 5 dB, and the same
procedure is repeated until the tone is audible for less than a minute. The lowest
intensity for which patient is able to hear the tone for about 1 min. is considered as
threshold at that frequency for tone decay test. Similarly, the testing is done for other
frequencies and the relation between threshold and frequency is obtained.
4.3
Short Increment Sensitivity Index Test
The Short Increment Sensitivity Index (SISI) test is used to detect the
pathology in cochlear or retrocochlear lesions. The operator selects the test frequency
and sets the level to 20 dB suprathreshold level. The tone is presented with brief
bursts of 1 dB / 3 dB / 5 dB increment for 300 ms at every 5 s interval. The patient is
asked to press the response button whenever he detects a change in the level. 20 such
bursts are given and out of them, the number of bursts the patient is able to detect is
recorded as percentage. The same procedure is repeated for each frequency, and the
audiogram is plotted.
4.4 Speech Audiometry
Speech audiometry testing attempts to address the integrity of the entire auditory
system by assessing the ability to here clearly and to understand speech
communication. There are two types of speech audiometric tests, ‘speech
discrimination test’ and ‘speech reception threshold test’.
In Speech discrimination test, lists of monosyllable speech discrimination words
are presented over earphones for each ear which patient is asked to repeat. The
percentage of the total number of words presented which the patient is able to identify
correctly gives the speech discrimination score (SDS) in percentage. In Speech
reception threshold (SRT) test, for estimating SRT, a group of 6 spondee words (two
syllable words with equal stress) is presented at 25 dB above the average pure tone
audiometry threshold for 500 Hz and 1000 Hz, and then at successively lower
intensities. When the level is such that the subject is able to identify 3 words out of 6
correctly, the level is taken as SRT.
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