GSi 61 - Page 61

It is difficult to maintain consistent supra-threshold responses to auditory signals in the
presence of several levels of noise in the same ear. Masking noise can cause confusion
and interferes with the ability to judge the loudness of signals.
Using earphones or speakers in a sound field, establish a recorded binaural spondee
threshold (SRT
1
). Live voice (Mic) or recorded (Ext A or Ext B) spondees may be routed to
each ear (Left/Right) through Channel 1.
Raise the speech signal to SRT
1
+ 5 with the Channel 1 attenuator without interruption.
Speech noise is introduced to both ears (Left/Right) through Channel 2 along with the
words.
Speech noise is introduced at a low level (0 dB HL is suggested) and is increased in 5 dB
increments with the Channel 2 attenuator for each spoken spondee until the intensity level
is 20 dB below the SRT
1
+ 5.
Obtain the “noise detection threshold” (NDT).
Obtain the “noise interference level” (NIL) by increasing noise in 2 dB steps (Channel 2)
until the patient stops repeating the spondees.
Maintain speech signal intensity (Channel 1) at the same level while increasing the
intensity of the noise (Channel 2) in 5 dB steps to a level 20 dB above NIL. Present one
word at each increment level.
Maintain the noise at this level (Channel 2) and reduce the intensity of spondees in 5 dB
steps (Channel 1) to a level 15 dB below SRT
1
. Present one word at each decrement.
Decrease the level of noise in 5 dB steps (Channel 2) for each spoken spondee until NIL is
reached. Continue to decrease noise level and note the level at which the patient begins to
again repeat spondees.
Reestablish a speech threshold (SRT
2
) as in Step 1.
Modified Doerfler-Stewart Test
This test is performed in one ear, using pure tones and white noise as a masker. Routing
selection for Channel 1 (Tone) and Channel 2 (White Noise) should be the same for the ear
being tested (left or right).
4-11
Chapter 4 - Special Test Procedures
Doerfler-Stewart Test
1.
2.
3.
4.
5.
6.
7.
8.
9.
1761-0100 Rev. B