Question
What is the goal of frequency lowering technology in hearing aids, and how is its effectiveness clinically verified for a patient?
Answer
The primary objective of frequency lowering technology is to improve speech intelligibility for individuals with a severe-to-profound high-frequency hearing loss for whom conventional amplification may be insufficient in making crucial high-frequency speech cues audible, such as the ”S” and “SH” sounds. Frequency lowering technology provides an alternative path to high frequency speech cue audibility by shifting this high-frequency input content down into a lower frequency output area that is aidable for the listener. Put another way, this process takes inaudible high frequency speech cues and moves them to a frequency range where the patient has better hearing, thereby restoring access to important components of speech that are critical for understanding.
To objectively verify the effectiveness of a frequency lowering fitting, a specific clinical protocol has been developed using Speechmap real-ear measurement technology. Once standard hearing aid verification and target acquisition efforts have been completed in Speechmap, the clinician can select and use a provided calibrated “S” stimulus presented at normal conversational speech levels to determine its audibility under the existing hearing aid settings. (It is important to note that any noise reduction feature presently utilized in the hearing aid programming must be turned off, to ensure that the “S” stimulus output is not impacted by this feature.) If the output measured when this 'S' sound is presented produces no supra-threshold energy, then frequency lowering may be needed.
To assist in setting the frequency lowering technology appropriately, clinicians are directed to use a targeting tool called the Maximum Audible Output Frequency (MAOF) range. This MAOF is calculated based on the speech-based real-ear aided response result obtained with normal conversational speech input that was acquired during the initial Speechmap verification procedure. With the Verifit 2, this target range can be automatically highlighted in Speechmap. Once the MAOF target is visible on the Speechmap fitting screen, the clinician again produces the “S” stimulus condition and subsequently adjusts the frequency lowering settings of the hearing aid until the downward slope of the aided 'S' output hump is positioned within the patient's Maximum Audible Output Frequency (MAOF) target range. This methodology helps ensure that the 'S' sound is just audible enough without being overly aggressive, which could interfere with other audible speech cues present in this output frequency region.
As a final step, the protocol includes an optional but valuable verification procedure using a calibrated “SH” stimulus. With the same frequency lowering settings in place based on the above “S” stimulus procedure, the audibility signature (output elements that are supra-threshold) of the “SH” stimulus can be obtained. If the audible output signature for the “SH” stimulus is distinctive when compared to the audible output signature of the “S” stimulus, then evidence that these two frequency lowered speech cues should be perceived distinctively by the patient has been obtained.
This systematic approach allows clinicians to objectively measure, adjust, and verify the performance and efficacy of frequency lowering fittings, regardless of the specific manufacturer's technology being used.
Learn more about frequency lowering with this course from Audioscan: Frequency Lowering Verification presented by Dave Smriga, MA
Learn more about Audioscan technologies visit https://www.audioscan.com/en/