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Thresholding Algorithm—Aligned Extraction
different amplitudes will have slight timestamp offsets relative to each other.
While the size of these timestamp errors or “jitter” is too small to cause problems
in most spike train analyses, it does have a significant effect on spike sorting: it
causes smearing of clusters in feature space.
The basic problem with threshold timestamping is that it does not use an
unambiguous feature (in time/voltage space) of the spike as the reference to
which a timestamp is attached. The obvious choice for such a reference is the
largest peak within the spike. The Offline Sorter System aligned extraction
thresholding algorithm uses this approach.
Here is an example of the difference between standard threshold crossing (top)
and aligned extraction (bottom). Note how the waveform “bundles” and the
corresponding PCA clusters are more well-defined when aligned extraction is
used:
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