MM402 - Introducing Audible Contrast Threshold: improve Your Hearing Aid Fittings in Just Two Minutes

Two patients with the same audiogram can have very different experiences using amplification. This is because the audiogram is a poor predictor how well a patient will hear in noise. The audible contrast threshold (ACT) is a test designed to provide a prediction of how well a patient will hear in complex environments and to improve the first fit of hearing aids.  Based on the principles of spectro-temporal modulation a threshold is measured in 2 minutes. The ACT value can then be used to automatically prescribe changes to the help in noise settings such as directionality and noise reduction. 

Summary:

For over 100 years we have made use of the audiogram to measure the quantity of hearing. We use this information to set the gain characteristics of hearings aids. In todays hearing technology, gain is only one part of fitting and the prescription of help in noise settings such as directionality and noise reduction is unfortunately often left to guesswork or trial and error. 

Over the last 15 years researchers have been looking into the area of spectro-temporal modulation (STM) as an area to give insights into the quality of hearing. The results have revealed  STM to be an effective tool to estimate hearing in noise ability. The challenge has then been to take this research and make this a clinically viable test which can have a true impact on the hearing aid fitting. The Interacoustics research unit (IRU) began its involvement with STM here and over the last 7 years has optimized the STM test paradigm to create ACT. ACT is a tool which can measure hearing in noise ability in just two minutes using the same equipment as pure tone audiometry. 

To measure the ACT a simple bracketing technique based on the Hughson Westlake test procedure is employed. Busts of noise are presented which have a modulated imposed on them to mimic a speech signal. The client will listen to these modulated signals and the audiologist will measure the contrast threshold or ACT value - the smallest level of modulation the client can detect. 

The ACT value can then be used to firstly estimate how well a client will hear in noise and secondly will automatically prescribe help in noise setting such as directional and noise reduction to the clients hearing aids. It will also identify when help in noise settings are not sufficient and remote microphone technology is required. 

The session will open with an exploration of the concept of spectro-temporal modulation and then explore how this psychoacoustic measure has been developed into a clinically viable test procedure. Time will be spent identifying how the result from ACT, the ACT value can be used is in the fitting process including both automatic and manual adjustment of hearing aid setting.