What is ASSR?
An auditory steady-state response (ASSR) is an electrophysiological response that is evoked by a periodically repeated (rapid) auditory stimulus. An ASSR typically uses frequency specific stimuli (0.5, 1, 2, 4 kHz) with the goal of creating an estimated audiogram. In other words, it is a test used for performing a threshold assessment.
Unlike auditory brainstem response (ABR) which looks at amplitude and latency of the response in the time domain, ASSR looks at amplitudes and phases in the frequency domain. Responses are detected using a statistic-based mathematical detection algorithm to determine if a response is present or not. Another difference is that while it is only possible to test one frequency per ear at a time in frequency-specific threshold ABR. ASSR allows for binaural testing; four frequencies in each ear at the same time (eight simultaneous presentations).
To convert the ASSR responses detected in nHL to eHL (estimated Hearing Levels), a correction factor is typically applied to each response to arrive at the final audiogram. Note that the estimated threshold cannot exceed 0dB eHL.
Figure 1: Estimated Audiogram in ASSR module
Why do ASSR?
The ASSR technology is completely objective and based on statistical probability rather than subjective assessment of response waveforms. The most important audiological application of ASSR is to provide an estimate of the pure tone audiogram, which is used for rehabilitation purposes.
How to test?
Patient Preparation is very important. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedance. It is recommended to have impedance values below 3kΩ or lower.
The same electrode placement for ABR is used for ASSR testing allowing for easy switching between the test types.
Electrode Placement (example)
Make sure that the patient is relaxed prior to starting the test. You can monitor this by watching the EEG. Window in the top right hand corner of the recording window. A relaxed patient will typically show black EEG curves within a ±40 volt rejection setting.
Setting up the Eclipse
The Eclipse ASSR software comes with pre-programmed protocols, so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinic need. Consult your manual to learn how to create or modify a protocol. The procedure described below is simply a suggested test process and to be used only as a guideline.
Basic ASSR Test Procedure
Starting ASSR from OtoAccess™ or NOAH
Performing an ASSR measurement
Other Helpful tools
Temporary change to Auto Test
Prior to starting a test, the default selection of frequencies to be tested can be modified in the “Stimulus” section in the upper left hand corner of the recording screen.
Disable or enable frequencies, change intensities, adjust parameters for patient arousal state etc., temporarily for this session. (See the manual for more information. Changes are effective in the current session only and will NOT permanently change the test protocol. Masking is also applied from the Temporary setup if required.
Browse between historical sessions
Use the PgUp and PgDn keys to toggle between historical sessions. Or select them manually from the Menu bar.
Toggle between 40Hz & 90Hz stimulation rate
Two different stimulus rates are available: 40Hz and 90Hz. 90Hz is typically used for infants and sleeping adults while 40Hz is gaining popularity for its typically strong response in awake adults.
Ctrl + S Save session
Ctrl + P Print session
Ctrl + F7 Temporary setup F2 Run test
F4 Pause / resume test F7 Report
Alt + X Save and exit
This Quick Guide is intended to provide information at a beginner level to assist the reader in their understanding of Real Ear Measures (REM). It will also explain some of the common terminology used for REM and within the Affinity 2.0 and Callisto™ software.
Why perform Real Ear Measures?
Not all hearing losses can be resolved by the same method, there are often many differences in the type of
Hearing Devices they are prescribed, the patient’s unique ear canal acoustics and the method in which the
Hearing Device is passing sound into the ear. Real Ear Measures help to overcome these differences by allowing the Audiologist to objectively measure and verify the sound that is being delivered at the ear drum.
The benefits of this process can be applied in varying scenarios from initial hearing aid fitting to troubleshooting. As a consequence, performing this method can help to gain better satisfaction from your patient from their first fitting and less follow up appointments.
REM can only be performed for Hearing Devices which deliver sound via an Air-Conduction method and not for devices which deliver sound via Bone-Conduction or Electrophysiological stimulation.
REM can be performed via three methods, Real Ear Insertion Gain, Real Ear Aided Gain and Real Ear Aided Response. All three achieve the same objective in fitting the hearing aid for the patient and they are all equally as efficient as one another. It is just a preference of which method is used.
What is the basic process of REM?
REM mainly involves placing a fine probe microphone into the ear canal to measure the sound at the ear drum. These measures include the response of the ear canal acoustics and the hearing aid and can help the clinician to adjust the hearing device specifically to the patients’ ears.
The REM process usually involves the following steps once hearing assessment has been performed.
This process sets up the conditions to allow comparison between the external microphone and the internal probe microphone. Once placed in the ear canal this will show the effect of the ear canal and hearing device amplification.
The calibration can be checked in the upcoming REUG measure through running a measurement in the same configuration as the calibration. When this is done a flat trace with a gain value at 0dB should be shown, please see the example below.
Performing this measurement allows you to make a consideration of the ears natural amplification of sound; this ensures that you are not fitting your hearing aid to over-amplify in certain regions of the frequency response.
Real Ear Occluded Gain (REOG) – this measurement involves the placement of the hearing device on the ear but muted/off. It allows consideration of the attenuation caused by the ear-piece and its obstructing effect of external sounds. This trace is usually performed with the REUG in view so that they can be compared – the difference between these curves is the amount of attenuation that the ear- piece is providing.
Real Ear Aided Response (REAR) or Real Ear Aided Gain (REAG) – this is a measure which involves the enabled/on hearing device being positioned on the ear with the ear-piece inserted as per normal use and the probe microphone inserted. This allows measurement of the hearing device’s amplification effect within the patients’ ear and includes the effect of the patients ear acoustics. This measure can be run at varying intensities but it is recommended that it is run at speech level (65dB) to ensure that the device is analyzed for the intensity that it will normally be used for.
It is often during this measurement that adjustment to the Hearing Device Manufacturers software is performed to help match a prescription target.
Real Ear Insertion Gain (REIG) – this is a measure which is performed in the exact same configuration as the REAR and REAG above but requires the REUG to be performed in advance of it. It does this because it only displays the dB gain view of what the hearing aid is doing and removing the REUR acoustics from this display. Please see the example of this below.
Again, it is common to make adjustments in your Hearing Device Manufacturers software to alter the response towards the prescription target following this measure.
It is essential to perform REAR, REAG and REIG at normal speech level (65dB) and some prefer to measure and adjust for soft (50dB) and loud (80dB) intensities also.
When do I use Calibrate for Open Fit?
When performing REM the stimulus needs to be maintained at the point of the patients head to ensure an accurate measurement is made.
This can be difficult when making REM measurements with Open Fit Hearing Aids because there is a lot of sound which leaks out of the ear canal and on to the reference microphone. Therefore the method used to perform REMs needs to be changed.
The two methods used are as follows:
Active Reference Method – this involves the external reference microphone on the REM headset monitoring and altering the stimulus from the speaker during the measurement. This is the best method to apply when measuring with occluding ear-pieces as there is minimal sound leakage onto the reference microphone.
The Affinity2 and CallistoTM is performing REM by default under this method.
Substitution or Stored Equalization Method – this involves a quick measurement prior to performing your Real Ear Measures to store the distance of the headset from the speaker. This ensures that constant signal intensity is maintained to achieve the measurement level at the patients head. However, this requires your patient to be very still to ensure an accurate measurement.
This method of performing REM is activated following ‘Calibrate for Open Fit’. This can be added as part of your REM test battery.
In the field of audiology, we are often presented with different quantities expressed in units of “decibel”. This quick guide offers you an overview on the most important details to know about the decibel at a glance.
What is a decibel?
It takes its name from Alexander Graham Bell, the inventor of the telephone. The dB (a 10th of a Bel) originally derived from the attenuation of a signal transmitted along a mile of telephone cable. The dB was linked with audiology from the beginning because this mile of attenuation was considered the smallest amount of signal change that could be detected by the average listener.
The decibel suffixes
In audiology, many different suffixes are appended to the unit of the dB. The most commonly used are dB SPL and dB HL.
Sound Pressure Level (SPL)
dB SPL is the measured pressure relative to 20μPa (micropascals). Historically, this 20μPa reference was selected because ir was the quietest sound pressure level that could be detected by a group of normal hearing test subjects.
dB SPL is an absolute and frequency independent unit. It is the unit often used in the calibration of signals in hearing testing equipment. All other suffixes used in acoustics to describe loudness are calculated from the SPL value.
Hearing Level (HL)
dB HL is used to refer to the hearing ability of a person and gives a statement about the severity of the hearing loss. Hearing levels are measured with pure tones at different frequencies and the hearing level of an individual will vary depending on the frequency chosen.
0 dB HL is what normal hearing is defined as. If a person has a hearing loss of 60 dB HL at 1kHz, he or she can’t hear a pure tone that is presented below 60 dB HL.
Normalized HL (nHL)
The notation of nHL is a reference to the frequency specific threshold of normal hearing subjects and describes the intensity level of stimuli used in the field of electrophysiology (eg. ABR, ASSR etc.). We use a correction factor added on top of SPL value to calculate the nHL value.
The Affinity 2.0 and Callisto™ software suites have the ability to allow custom print layouts to be created and used alongside the VIOT Suite and Titan Suite. This enables data from various tests to be combined into one convenient printout.
Creating a Custom Print Template
Opening the Print Wizard:
You can access the setup for protocols from any of the AUD, REM or HIT (Affinity 2.0 only) tabs.
Press, Menu, Setup and then AC440 Setup (or REM440/HIT440 depending on which module you are in). Performing this action will open a new window.
In the new window you will find Print Setup in the bottom left corner. Please press this to open the Print Wizard.
Designing a New Customised Print Template
Click on the blank page in the top right of the screen to create a new print layout. This action will open a new screen. You can alternatively right click on an existing print layout and select Edit to continue building it.
Once in this new screen you will see the elements which you can add to the layout on the left of the screen. These are ordered by their corresponding test module, for example everything to input into the print template to do with the AUD module can be found under AUD.
All of these elements are able to populate on printing should the patient have these test types assigned to their profile in your patient management system, Noah or OtoAccess™.
Please select an object from the left to draw onto your page. In this example I am using an Audiogram. Once Audiogram has been clicked you will need to draw it to your desired size onto the page.
Once drawn you will be able to move it to your desired position and also right click to define the parameters of what information it displays. For example, in this instance right clicking on the object will allow you to ‘select type’, clicking on this will open a new window which will allow you to define options such as the test ear and include sound examples etc. Every object you input allows for customization of the options the element can display, and the options available to each can vary depending on the module element selected.
Also, when right clicking on an element you have the options to rotate that element and also toggle the surrounding border.
Once you have clicked in all of your elements and have configured them to your preference you will need to organise them. This can be done by moving them to their desired position and sizing them similarly also. There are a few tools to assist you with this. If you left click on an element you will notice the highlighted tool bar below become active. The options available to you’re here are purely for ordering (ex: to send items backward/forward).
However, if you left-click on one element and then hold Control on your keyboard and left clik on another you will then be able to activate the rest of this tool bar. This opens up the sizing and alignment options to you. Hovering your cursor over each icon in this toolbar will explain its function.
These settings make it easier to match the sizes of the elements you have added to your print template.
I have performed the ‘make equal size’ option below as an example.
Notice how the first element clicked is taking settings (size) from the second element.
Continue to click and add further aspects of your print template to your preference. Once completed you can add information on your clinic (via a blank Test box) and even a logo. This can be done via the General sub-tab on the left of the screen.
Drawing a logo element will allow you to create a section on your print template for which you can import a .jpg file. To do this, right click on the element and click Select image... This will open the system dialogue where you can navigate to the image that you wish to input. Please note that the Print Wizard only accepts .jpg and .png format image files.
Finally I will add a text box below the logo to show the sites address and contact details.
You can also alter the font and formatting of the text and how it will appear on your print layout in this section. This text box will be common to this print layout when it is printed from in the future.
Saving your print template
As this is a new print layout Save will perform the same action as Save As... and a small window will appear requesting you to title your print layout.
Once you have titled this layout and Ok is clicked it will appear in your Print Wizard as a new layout.
Please see the Quick Guide titled ‘Quick Guide – Print Report’ on how to set this as a default or a favorite. Should you require additional information on this then please see the Affinity 2.0 and Callisto™ Additional information guides.
Using the Print Wizard
In the Print Wizard you have the option to create customized print templates which can be linked to individual protocols for quick printing. The Print Wizard can be reached in two ways.
There is an additional quick guide to explain how to create a template, it is titled ‘Quick Guide – Customised Printout Setup’.
Now the Print Wizard window opens and shows the following information and functionalities:
Right clicking on a specific template provides a drop down menu offering an alternative method for performing the options as described above:
Further information on this can be found in the Callisto and Affinity Additional Information Guides.