Assr; About The Assr Module; Brief Introduction To Assr; Analysis - Interacoustics Eclipse Additional Information

Eclipse Additional Information

6 ASSR

6.1

About the ASSR module

The Eclipse ASSR (Auditory Steady-State Response) is intended for use in the recording and analysis of hu-
man physiological data for the diagnosis of auditory and hearing-related functions. The target population for
Eclipse ASSR includes all ages.
ASSR is used for objective threshold evaluation. The ASSR test consists of a switchable recording view and
audiogram. The user can switch at any time during and after testing between these views. The results are
typically used for hearing aid fitting for individuals that cannot take part in a behavioural threshold examina-
tion.
For the purpose of a diagnostic evaluation a narrow band (1 octave wide frequency specific NB CE-Chirp®)
stimuli are applied.
6.2

Brief Introduction to ASSR

An auditory steady-state response (ASSR) is an electrophysiological response that is evoked by a periodi-
cally repeated auditory stimulus. The response is stable over time as long the stimulation is presented. If the
recording time window can be regarded as being infinitely long, then the response will consist of a series of
discrete frequency components that are constant in both amplitude and phase over the time window.
Auditory steady-state responses are to be distinguished from auditory transient responses. Auditory steady-
state responses are evoked by a series of sound stimuli that are presented at a high repetition rate, whereas
auditory transient responses are evoked by an individual, brief sound stimulus or a series of brief sound stim-
uli that are presented at a low repetition rate.
At medium repetition rates there is a grey zone where the differentiation between the two response types is
difficult to make. However, if the stimulus repetition rate is so high that the electrophysiological response to
one stimulus overlaps with the response to the next stimulus, then the recorded activity can be meaningfully
classified as a steady-state response.

6.2.1 Analysis

ASSR stimuli can be designed in the time domain or in the frequency domain and both approaches have ad-
vantages and limitations.
Time domain
Similar to the classical representation of ABR, the ASSR can also be displayed and analysed in the temporal
domain when averaging in the time domain has been chosen, it will be quite natural to evaluate the result as
a waveform in the temporal domain. Here the standard amplitude and latency characteristics may be ex-
tracted and calculated.
With the design in the time domain the temporal characteristics of the stimulus can be accurately designed
(clicks, tone or noise bursts, amplitude modulation etc.), however, the spectral characteristics may be less
precise.
Frequency domain
Due to the overlapping response waveforms which create the ASSR, analysis in the time domain may be dif-
ficult and a clear resemblance to the familiar waveforms obtained at lower stimulation rates may be com-
pletely missing. However, ASSR can be much more efficiently displayed and analysed in the spectral do-
main, because the response consists of specific frequency components that are linked to the stimulus repeti-
tion rate. If the stimulation repetition rate is 90 stimuli per second (i.e. 90Hz) the ASSR will have spectral
components at 90, 180, 270, 360, 450, 540Hz up to the twelve harmonic frequencies.
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