Interacoustics Eclipse Additional Information page 230

Eclipse Additional Information Page 220
MMN Test: Mismatch Negativity Test. A test designed to retrieve the MMN response phenomenon, which is
present approximately 250ms after stimulus onset. The MMN is present on a calculated differential curve
found by subtracting two waveforms where one is recorded with a frequently appearing sound stimulus and
another recorded with a rare appearing different sound stimulus. Unlike the P300 patient does NOT need to
pay attention to the stimuli.
See also P300.
nHL: See Calibration
NuPrep: Trade name for a widely used skin preparation paste.
OAE: Otoacoustic Emission
P300: A test designed to retrieve the P300 response phenomenon, which is present approximately 300ms
after stimulus onset. It occurs as a response to a stimulus, which differs from a stimulus to which the patient
is accustomed. The rate between the accustomed stimulus and the rare stimulus is approximately 80/20.
The patient must be alert for the response to be present. (Pay attention to stimuli)
peSPL: See Calibration
Pip: Same as Tone Pip – see tone burst. The term "logon" is also sometimes used to mean a brief tone
burst.
Polarity: The polarity of a sound stimulus indicates which direction the diaphragm of the transducer moves.
This is primarily important for clicks, as a click consists of an activated movement in one direction only.
Pre Amplifier: Also referred to as Biologic Amplifier. This important piece amplifies the very weak signal
from the electrodes into a signal sufficiently strong for the digital circuits of the ABR unit to handle. Doing this
without adding any additional noise either from its own electrical circuits or from electromagnetic stray fields
in the vicinity of the patient (Common Mode Rejection) are key elements to Pre Amplifier performance.
Rarefaction (polarity): The polarity of a sound stimulus indicates which direction the diaphragm of the trans-
ducer moves. Rarefaction makes the diaphragm move away from the ear, producing a negative pressure in
the ear canal. Considerations of polarity are primarily important for clicks, as a click consists of an activated
movement in one direction only. Waveforms based on Rarefaction stimuli and waveforms base on Conden-
sation stimuli have slightly different morphology due to the difference in movement of the basilar membrane
and the resulting differences in the generated electrical response. Each stimulus type performs well for ABR
recordings.
Rejection: Rejection is a process whereby Epochs below a certain quality level are disregarded in the aver-
aging process. Normally rejection is carried out by evaluating the general electrical level of the EEG con-
tained within an Epoch. This is a good system, because high EEG levels primarily consist of potentials stem-
ming from muscular and other non-related activities. Incorporating Epochs with an unacceptably large ampli-
tude (caused by excess muscle activity into the averaging would cause degeneration of the waveform).
Technically it is necessary to incorporate a rejection system, as the digital circuitry can only handle signals
up to a certain level – every Epoch holding signal above that level must be rejected.
Therefore it is obvious that the gain provided between the electrodes and the digital circuitry plays an im-
portant role in the rejection system: If you lower the gain, more Epochs will be accepted, and if you apply too
high gain, most all Epochs will have an electrical level too high to be acceptable. This unit offers an auto-
matic gain setting feature, which will adapt to the patient throughout the test, thus obtaining the best wave-
form possible under the given circumstances. Each amplifier gain setting has an associated maximum rejec-
tion limit above which Epochs are rejected. The appropriate setting of the rejection level is crucial for obtain-
ing good quality (low noise) recordings. A new feature now allows the rejection level to be lowered in fine
steps for optimum selection of the level at which Epochs are accepted or rejected, thus allowing the operator
to optimize response quality for the test conditions and degree of patient relaxation.
Rejection systems play an important role in assuring waveforms of high quality.