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Binaural Hearing Study Report

Posted May 21 2010 12:00am

Lily did really well in the Binaural study in Madison. However you can see the challenges she faces as compared to normally hearing kids.  Here are some of the results.   

Measures of Sound Localization

During testing, the child sits in a quiet sound booth, facing an array of loudspeakers. The phrase “when I hide I go….” Followed by white noise bursts are emitted from loudspeakers and the child is trained to reach for the sounding object, which is hiding behind a curtain.

A.    Right-Left Discrimination
This task provides a general measure of the child’s ability to indicate whether a sound source is presented from a location that is to the right vs. left, and we look for the smallest angle for which a child can choose between right and left consistently and with 80% accuracy. Children of this age who have typically developing hearing who have been to our lab for testing can typically perform this task at 90-100% correct for angles of 15 degrees.

Results:  Lily was able to perform the task very well when wearing both of her CIs. At 60 degree separation she was 100% correct. At 30 degrees she was 80% correct and at 15 degrees she was 70% correct. When tested monaurally (with her first CI), she was able to perform the task at 60 degrees, with 100% correct. However, she was at chance (50%) at all other angles, suggesting that she had a significant bilateral benefit on the task.

B.    Localization
Sound localization provides a measure of spatial hearing ability that requires more challenging processing by the auditory system. The “target” is also a brief sentence followed by noise bursts, presented from one of 9 possible speakers. Lily was asked to perform this localization task approximately 27 times, and we calculated her errors for all the testing as a whole with a statistical value known as Root Mean Square (RMS). The closer a child’s response is to the true sound location, the smaller the RMS. Children with typically developing hearing have RMS errors of 10-20 degrees, which means that, on average, their localization of the sound source can be 10-20 degrees away from where the actual sound was presented.

Results:   Lily’s RMS error was approximately 30 degrees. This is similar that our average results collected in children who are older (4-12 years old), and actually better than numerous children in the older age group. This finding suggests that Lily is able to localize sounds at better than chance (which is around 50 degrees) and at least as good as many older children who use bilateral CIs.

Speech Understanding in Background Noise

The child hears spondaic words coming from the front of the room. The child is asked to tell the tester what the content of the sound was.  The male speech voice is accompanied by two women talk at the same time. The child is asked to ignore the women's voices and report the content of the speech. The volume of the spondee is decreased to find a Speech Reception Threshold (SRT).  An SRT score indicates the softest level at which the child was able to correctly identify the target word 79.4% of the time. This is intended to simulate real-room listening situation such as classrooms.

Results:                            Bilateral             Unilateral
       Front Competitor        45 dB SPL            51 dB SPL
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