Negative EEG and EMG artifacts cannot be detected by Artifacts detection option of the Sleep Scoring protocols
Sleep scoring protocols in NeuroScore include the Artifacts detection option that allows the user to enter a positive threshold of the amplitude above that the signal will be considered an Artifact.
Nevertheless, negative artifacts such as large negative spikes or data loss segments like in the example below, cannot be detected with this Artifact detection option.
This issue occurs in NeuroScore versions below version 3.4.0. It is recommended to upgrade NeuroScore. Otherwise the workaround suggested in the Solution below may be applied.
This article is introducing an workaround for this problem. The main idea is to add a derived signal which is identical with the original signal except for the negative artifacts that are transformed into positive artifacts in order to have them detected with the Artifact detection option included in the sleep scoring protocol.
Here are the steps:
- Right click in the graphic representation of the signal and choose Add Derived Signal..
- In the New Derived Signal window select Transform and add the expression iif(X<A,-x,x) where A has to be a numerical value (in Volt) for the negative amplitude threshold that you want to set.
In the example below , the negative threshold A is set to -2mV=-0.002V. Please note that the A value entered in this expression for biopotential signals has to be in Volt.
The new derived signal generated with this expression will be identical with the original signal, with the exception of the data points that have an amplitude x lower or equal with A. For these data points the expression will return positive amplitude values that will be detected by the Artifacts detection option in the sleep scoring protocol.
This is the representation of the new derived (transformed) signal:
The sleep scoring protocol should be applied on the derived (transformed) signal, not on the original signal, in order to detect all (positive and negative) artifacts.
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