I want to tell you about a new reason why this is a good time to be an audiologist.
The Food and Drug Administration recently approved the marketing in the U.S. of a new test system called HEARLab. The system was researched and developed in Australia by the NAL (National Acoustic Laboratories). It is manufactured in this country by Frye Electronics, based in Tigard, Oregon.
Like ABR (auditory brainstem response) test equipment, this new system measures evoked responses. However, unlike ABR, HEARLab measures cortical responses, not responses generated in the brain stem. The proper name for these cortical responses is CAEP (Cortical Auditory Evoked Potentials). HEARLab presents signals to the patient and then measures and quantifies the electroneural responses generated by the neurons, just under the scalp.
The new system performs two separate tests: ACA (aided cortical assessment) and CTE (cortical threshold evaluation). In this post I am going to explain ACA.
USING ACA: HOW AND WHY
When you fit a hearing aid on a child, infant, or adult with dementia, you cannot ask questions like: “How well do you hear me? Does the sound need to be louder?” In the absence of feedback from the patient, pediatric audiologists tend to fall back on their experience and on the DSL i/o fitting formula or other hearing aid fitting strategies.
The new HEARLab test, NAL-ACA uses a sound field speaker (like the speaker used with your real-ear system). Three digitally modified speech sounds are presented to the patient and the evoked response is displayed and studied. The purpose of the test is to see if the amplification is strong enough to elicit an electrical response in the auditory cortex. If the amplification is too weak, no cortical response will be observed.
The test uses three speech sounds: /m/, /g/, and /t/. The test sounds have been extracted from continuous speech, with the noise filtered out. The /m/ sound has its maximum energy in the lower frequencies; the /g/ has it in the mid-frequencies, and the maximum energy of the /t/ is in the high frequencies. Speech sounds are used as stimuli because we are interested in the patient’s reception (detection) and perception of speech. These three test sounds can give us helpful diagnostic information about how a patient hears speech sounds in different frequency regions.
The HEARLab system has three presentations levels for the ACA test: 55, 65, and 75 dB. The default testing level is 65 dB SPL, the level of “normal speech.” The other two test levels, 55 and 75 dB SPL, are provided to make it easy for the audiologist to increase or decrease the input level.
HERE’S THE PAYOFF
When parents see us doing the ACA test, their most common question is, “What are those numbers showing us?” The fun and excitement come when we can tell them, “You see that little check mark in that box? That is your baby’s brain saying, ‘Yes, I can hear that sound!’”
Our profession began with basic hearing tests. Next, brain stem testing became part of our “tool box,” and later we added tympanomentry, ENG testing, real-ear tests, and measurement of OAEs (otoacoustic emissions).
Now, HEARLab’s NAL-ACA test provides audiologists with a brand new and very useful tool. It allows us to obtain valuable information about pediatric patients and others who cannot speak for themselves. It tells us whether or not a sound is detected by the patient’s brain. I expect this test to become the gold standard in pediatric hearing aid fittings.
Present a sound…study the evoked response with and without a hearing aid…and look to see if the sound is detected by the auditory cortex. Isn’t it fun to be an audiologist!
In addition to owning and running a private audiology practice in the San Diego area for nearly 40 years, Robert L. Martin, PhD, is a Senior Trainer for Frye Electronics.
