2.4.2 Speech Reception Threshold and Spatial Release from
Masking
Speech perception in noise was evaluated using the speech reception
threshold (SRT) test. The target
speech
signals of disyllabic words were always presented from the front
loudspeaker positioned at the ear level at 0° azimuth, with the masker
competitor stimuli of SSN presented variously at the ear level at the
three different azimuths (0°, -90°, and +90° azimuth). Masking of SSN
was presented at a fixed level of 65 dB SPL, while the level of the
target speech signals started at 65 dB SPL and varied adaptively to
estimate the result of SRT depending on the participant’s response. The
level of subsequent disyllabic words was adjusted adaptively in 2-dB
steps. SRT was defined as the intensity level of the speech signal
presented when the participant had a 50% correction of disyllabic word
identification. The speech-to-noise ratio (SNR) was defined as the
difference between the speech and noise levels when the patient attained
50%-word recognition (SNR
dB
SPL=SRT dB SPL-SSN dB SPL). During the test of speech perception in
noise, both ears remained open.
For the SSD group, the following spatial speech-in-noise configurations
were used: (1) Co-located condition: both the target speech and SSN were
located in the front (0°, azimuth); (2) Separated condition in
S0NNH (SeparatedS0NNH):
the target speech was located in the front (0°, azimuth) and the SSN was
at the NH side (-/+90°, azimuth); and (3) Separated condition in
S0NSSD(SeparatedS0NSSD): the target speech was located in the
front (0°, azimuth) and the SSN was at the impaired side (-/+90°,
azimuth). For the NH group, the SSN was uniformly presented from the
left side and had only two test conditions: Co-located and Separated.
SRM was computed as the difference in SRT between Co-located and
spatially Separated conditions (SRM in dB
SPL=SRTCo-located dB SPL -SRTSeparateddB
SPL).