By Steve Hallenbeck, AuD
Hearing aid features which rely on wireless communication between the devices have become standard fare. Except for features which are easily observable and straightforward, such as the transfer of pushbutton and volume commands from one hearing aid to the other, audiologists must put their faith in manufacturers’ explanations of how – and if – things work as intended. This presents an obvious dilemma in the context of evidence-based practice.
Recently, my colleague Tammy Stender and I posted a response to the question “How do you verify binaural features in hearing instruments?” on the Ask the Expert section of www.Audiologyonline.com. This post walked readers through how to check ReSound Binaural Directionality with the Otometrics Aurical testbox. Since then, we have had requests from audiologists who would like to try this verification technique on other equipment. Since the Audioscan Verifit is commonly found in practices across the US – and because we also happen to have two of these in our clinic – we put together the following guide for using this equipment as well.
Hearing Aid Setup:
Use the “Binaural Directionality” environment and set hearing Aids to a flat test gain setting. I recommend 10 dB flat gain for all inputs. Turn off all other features and reset the environmental optimizer to zero.
Binaural Directionality Test (one testbox method)
Keep track of which is the right and which is the left hearing aid. The changes you will be looking for will take 20 to 30 seconds to occur.
1.) Place the left hearing aid in the test box.
2.) Start the Verfit directional test. Use 65 dB of noise only. Keep the right hearing aid in your hand or on a desk.
3.) With the noise only in the test box and no speech outside the test box, the left aid response should be omnidirectional.
4.) Begin speaking with your orientation in front of the hearing aid outside the test box. I have used the rainbow passage but continuous conversational speech can also trigger the change. After approximately 20 seconds of speech outside of the test box, the hearing aid inside the test will change to a directional pattern.
5.) If you stop speaking and use a noise generator to introduce more than 65 dB of noise outside of the test box, the test box aid should return to an omnidirectional setting.
6.) You can repeat the test in a basic program with all features and the environmental optimizer set to zero. You should see no change in the test box instrument.
Binaural Directionality Test (two test box method)
1.) Place each aid in a separate test box, keeping track of left and right.
2.) Start the directional test in each test box using 50 dB of noise only à each HA should be in Omnidirectional
3.) Increase the test signal in each box to 65 dB of noise onlyà the right hearing aid will go into directional mode.
4.) Change the right aid test box to speech in noise with the level at 65 dB and the SNR at 9 dBà the left aid will change to a directional pattern and the right aid will change to an omnidirectional pattern.
5.) Change the left aid test box to speech in noise with a 65 dB level and an SNR of 9 dB and change the right aid test box to 65 dB of noise onlyà the left aid will change to an omnidirectional pattern and the right aid will change to a directional pattern.
6.) Change the right aid test box to speech in noise with 65 dB and the SNR at 9 dB (both test boxes are set this way in this step)à the left hearing aid will change into a directional pattern and the right hearing aid will remain in a directional pattern
7.) Set both test boxes to 50 dB of noise only and each device will return to an omni directional setting