What is ASSR Hearing Testing?

Advances in technology have greatly improved the neural responses generated by the Eclipse ASSR through the use of the CE-Chirp® family of stimuli, as well as the response detector which uses both phase and magnitude information, in addition to higher harmonic response components.

You can read the full transcript below.

What is ASSR?

Like ABR, ASSR is an evoked potential which is generated in the brain in response to sound.

Electrode montage

To record brain activity, we need to apply electrodes to the head of the patient. The most common montage is to have two reference electrodes, one on each mastoid, an active electrode, which is found on the high forehead, and the ground electrode placed on the low forehead or cheek.

What is the CE-Chirp®?

Just like any auditory evoked potential, we firstly need to present the stimulus to the patient. Eclipse ASSR utilizes narrowband CE-chirps. This stimulus has been proven to provide strong neural responses by accounting for the time it takes the stimulus to travel along the cochlea.

To use this stimulus in ASSR testing, we simply present the narrowband CE-chirp at a particular stimulation rate – for instance 90 hertz. This method evokes strong synchronous neural responses at 90 hertz which are easy to detect by the ASSR response detector.

The evoked potential device records this activity over time while looking for a response. If a hearing response is present, then it must reach a defined level of certainty before it is classified as a clear response.

Methods of determining the response

Historically, there have been two methods of determining the level of certainty of the response.

One method looks at the size of the response compared with the background noise and is called magnitude or amplitude-based detection.

The other method looks at the timing of the response compared with the timing of the stimulus and is called phase detection

Eclipse ASSR vs classic ASSR

Once one of these criteria were met and statistically verified, classic ASSR systems reported a response being present. The Eclipse ASSR uses both of these methods in combination, so both the phase and the magnitude of the response are considered.

More importantly though is the fact that Eclipse ASSR also looks at response components that none of the previous systems consider at all.

These extra response components are the higher harmonics of the response. What does this mean? Well, even if you stimulate at a rate of 90 hertz, then the response from the neural system is not only giving you a clean, 90-hertz signal back, but it also presents harmonic distortions of that 90-hertz response.

Now, harmonic distortion is a spike of activity which occurs at frequencies that are exact doubles, triples, and so on of the fundamental modulation and response frequency. So, with a fundamental stimulation rate of 90 hertz, the harmonic distortion components would be activity at the frequencies of 180 hertz, 270 hertz, and so on.

By not only considering the fundamental frequency but also looking at all relevant higher harmonic response frequencies, much more response information is available to the Eclipse ASSR response detector and that allows it to find even the smallest responses more efficiently and accurately.