Placement Of Bone Conductor - Interacoustics Eclipse Additional Information

Eclipse Additional Information
Even though the ASSR response detector can disregard artifacts to a certain degree, a likelihood of in-
creased number of false passes exists when large artifacts are present.
For ASSR testing the following guidelines should be followed, to reduce the risk of false passes, caused by
above mentioned stimulus artifact.
1. Always keep transducers and their cables as separated as possible from the recording cables.
2. For bone conduction ensure to keep as large a distance as possible from the bone conductor to the
surface electrode and its cable. Please refer to the section: Placement of bone conductor below.
The size of the artifact can often be monitored on the Raw EEG display (as shown in the example
above). The larger the artifact, the higher the risk is, of the artifact interfering with the recording.
For reliable recordings you must find a setup by which the artifact is not causing false passes. You
might check the biologic origin of the response, by lifting the bone conductor slightly off the mas-
toid/forehead as this should cause the response not to be detected (unless the child has good air
conduction hearing causing air conducted sound from the bone conductor to generate a response.
3. For insert phones, the red and the blue boxes generate the stimuli. These must as well be separated
from the recording cables. Checking for false passes can be done by clamping the tubes conducting
the sound from the box to the ear.
4. A rejection voltage of maximum 120µV is advised, as artifacts larger than this is almost certain to
cause an increased likelihood of false responses.

6.9.2 Placement of bone conductor

Stimulus artifacts will be present at intensities near maximum output when using the bone conductor. The
artifacts can be reduced by using an earlobe placement instead of mastoid placement. Placing the bone con-
ductor too close to the electrode causes artifacts and more noise in the recording. A good rule of thumb is to
keep the electrode and bone-conductor minimum 1 cm apart from each other, but more distance may be re-
quired to avoid large artifacts, and the bone conductor can be placed on the mastoid or elsewhere on the
temporal bone.
Consider bone conductor location before applying electrodes. High mastoid position is often preferred as it
might be 30dB more sensitive than forehead in infant (Lightfoot, 2010). Place the mastoid electrode below
the bone conductor for the largest ABR response but avoid a position on the neck muscle.
BC placement on the temporal bone slightly posterior to the upper part of the pinna provides similar ASSR
thresholds to a placement on the lower mastoid (Small et al., 2007).
Bone conductor headbands can be too big to fit the head of an infant and hand-holding the bone conductor
can be used for the mastoid position. Firmly hold the bone-conductor with a finger on the infants head.
Experiments on an artificial mastoid have shown differences of less than 1dB in stimulus level between fin-
ger pressure and standard force of 5N.
To avoid affecting the stimulus it is recommended to only hold the bone conductor with one finger and mak-
ing sure not to touch the pinna with the bone-conductor or the surface electrode.
It is recommended to start testing at moderate level (e.g., 30dB nHL) as higher intensities might wake up the
sleeping infant (Small et al., 2007).
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