Grason-Stadler GSI
®
61 CLINICAL AUDIOMETER
Alternate Binaural Loudness Balance (ABLB) or Fowler Test
The perceived growth of loudness of a suprathreshold tone in an impaired ear may differ
from the compared growth of loudness of a tone of identical frequency in the normal ear.
Recruitment, if present, may be found.
1. Assist the patient with the placement of the earphones.
2. Determine the threshold level for each ear at all frequencies being tested.
3. Select the ear to serve as the reference ear, typically the ear with the better hearing
sensitivity. This ear will receive the tone at a fixed intensity.
4. Select the ALTernate tone format. Channel 1 and Channel 2 will automatically interlock in
this selected format. The Interrupt button should be selected for automatic presentation of
the tone. The tone will alternate from Channel 1 at the rate of 400 msec on, 400 msec off
followed by Channel 2 at 400 msec on, 400 msec off.
5. The tone may be manually alternated between Channel 1 - Right and Channel 2 - Left by
pressing the tone bar (with the Interrupt in the off position) for the duration of the time the
signals are to be presented.
6. To increase the test reliability, the patient should be given several trials to judge whether a
variable tone is “softer,” “equal to,” or “louder” than the tone in the reference ear.
7. Set the intensity of the tone for each channel to 20 dB above the threshold of each
corresponding ear.
8. Alternate the tone presentation between the ears.
9. Keeping the intensity fixed in the reference ear, vary the intensity level of the tone
presented to the test ear. Record the level at which the patient judges both of the signals to
be of equal loudness.
10. Repeat the above procedure increasing the intensity of the tone for the channel routed to
the reference ear by 20 dB each time until an intensity of 80 to 90 dB is reached. Identify
the dB HL of the tone necessary to “balance” in loudness the tone in the reference ear at
each level. This procedure is followed for each frequency to be balance tested.
4-2
1761-0100 Rev. B
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