Interacoustics Eclipse Additional Information page 49

Eclipse Additional Information Page 39
Polarity
Stimulus polarity may be set to Rarefaction, Condensation or Alternating.
Rarefaction and Condensation will each provide slightly different waveforms and either is recommended for
normal ABR. Alternating polarity provides a waveform which is actually a combination of these two wave-
forms. Such a combination of waveforms may introduce some unwanted distortions to the waveform mor-
phology. The advantage of the alternating stimulation with ABR is that artefacts stemming from electromag-
netic radiation from the transducer can be cancelled. Bone conductors can generate very strong artefacts.
An insert phone has hardly any artefact due to its construction.
Tone Burst / Tone pips
The desired frequency of the tone burst is selected here. The following frequencies are available: 250Hz,
500Hz, 750Hz, 1kHz, 1.5kHz, 2kHz, 3kHz and 4kHz.
Sine Waves (applicable to Burst only)
The desired total number of sine waves cycles of the burst is selected here. Please note, that due to inaccu-
rate use of terms in some early ABR systems, you may see a stimulus be referred to as e.g. a 2-1-2 Black-
mann. This is a stimulus with a total of 5 cycles, and this slider should be set at 5.
The longer the stimuli (amount of cycles e.g. 28 cycles) the more frequency specific the stimuli becomes. But
it also means that fewer hair cells are stimulated and smaller responses are expected.
On the other hand if the stimulus is narrow, e.g. 2 cycles, the frequency range is much larger and it turns into
a click likely stimuli where most of the hair cells are stimulated. Larger responses are expected, but it also
means we cannot exactly tell which part of the cochlea response occurs from.
E.g. if the patient has a low frequency hearing loss, but some of the hair cells at higher frequencies work,
then the overall response from the narrow stimuli tells us incorrectly that the patient would have a normal
hearing.
Window (applicable to Burst only)
The desired window, which sets the rise and fall parameters of the burst, is selected here. E.g. "Blackmann"
is considered to have good frequency specificity. If you select "Manual" you must set the Rise/Fall and Plat-
eau.