Topics:
Pixels/pad
box.For imec probes,
shift+click or right-click on a viewer pad to select its LF graph.T
and antibounce Stay low
settings only apply to spike detection.Update (s)
interval to visualize infrequent activity.Raw data -> Fetcher -> Graphs -> Shank
Every tenth of a second a process thread called the 'graph fetcher' grabs the next chunk of raw data from the main data stream and pushes it to the Graphs window. The stepping of the visible time cursor across the screen heralds these events.
If the corresponding Shank Viewer is visible, the Graphs window pushes a copy of the unmodified raw data chunk to the Shank Viewer. Importantly, the filter choices in the Graphs window do not affect the Shank Viewer; each does its own filtering/processing.
Note that clicking Pause
in the Graphs window pauses/resumes both the graphs and the shank activity mapping.
The Shank Viewer applies a 300Hz highpass
filter to AP band channels and a 0.2Hz - 300Hz bandpass
filter to the LFP channels. These filters reduce out-of-band electrical noise, including DC offsets, which allows better comparison to your requested spike threshold voltage.
Average current window
counts spikes and tallies peak-to-peak voltages over the data currently displayed in the File Viewer window. The Shank Viewer updates as you scroll.
Sample whole survey
is specifically for viewing survey result files. It averages up to four half-second time chunks drawn from each of the banks on the probe to build a whole-probe activity map. You have to click Update whole survey
to trigger the calculation. If you change the spike threshold or 'stay low' values you need to click Update
again. Peak-to-peak calculation has no parameters so only one Update
click each is needed.
You can read an appropriate threshold level from a graph:
-<T>
(approximates Shank View filtering).This value gives you a rough spike width filter. Our spike detection logic requires that the signal cross the threshold (from high to low) and continuously stay low for at least this many samples.
Unfortunately, if you've got a lot of electrical noise, the signal could cross back and forth rapidly across the threshold. The detector thinks such spikes are narrow and they are rejected if 'stay low' is too high.
If your spike rates seem too low, try lowering 'stay low'.
To directly examine the noise in a selected graph:
Pause
button to freeze the display for a better look.Load
and view an existing file without applying.Default
to {bank-0, ext ref, std gains, std filter} without applying.Save
as a file without applying.OK
applies changes to new configuration.Cancel
reverts to prior configuration.Apply
changes to current run.Revert
to current settings.Pix/pad
box.Define your region(s) of interest:
Boxes
menu to the number of desired regions.Clear
removes all boxes.fin