Polhemus recording through Brainstorm on matlab runtime R2022b

Hello, I'm new to using the brainstorm digitization feature, and I could use some troubleshooting advice.
It appears that Fastrack Polhemus' configuration was successful. The tracking device is recognised by the brainstorm, but when recording, it provides two sets of xyz coordinates for a single button press. As a result, RPA is not being registered after Nasion and LPA. Additionally, no EEG electrodes are being recorded at all.


Hi @ritu;

Are these values the same, or are they different?

The values are different.

Can you send a screenshot of the captured values?

Have you tried to use the "Collect Point" with the mouse?
is it doing the same thing as the stylus?

Here are the screenshots of the coordinates recorded through stylus and collect point option respectively.
Both the procedures generate the same error.
I only collected for Nasion data point here, and LPA data point was filled automatically.

I've checked all the previous issues and this is the first time that we have faced this issue.
@Marc.Lalancette any idea for this one?

@ritu how many receivers do you have on your device?

Can you do the following:

Start Brainstorm
Start Digitize
in the Matlab command window, create the global variable
global Digitize
then print the SerialConnection info
you should have something like this:
Serial Port Object : Serial-COM6

Communication Settings
Port: COM6
BaudRate: 9600
Terminator: ‘LF’

Communication State
Status: open
RecordStatus: off

Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 1

then write to the serial port to collect a point

Can you share the outputs?

We have three receivers.

So this explains why then you are getting two values per acquisition.
If you want to use brainstorm digitize, you need just two receivers, the stylus plugged in channel 1, and then the fixed receiver plugged into channel 2.
PLease follow the instructions as stated on the tutorial.


Thank you. I overlooked that important part. We were using Neuroscan before, so went ahead with the same concept.


Looks like you've figured it out, but that's an interesting "problem" and it would be a shame to force users to reduce robustness or accuracy if they have more receivers. Possibly something we could eventually improve in the future.

I'm curious though, may I ask how you use those receivers? Do you place them all on the head, and how are they placed and attached?

[EDIT: never mind, I saw it in your picture.]


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Also, just in case the receivers are not the issue, I vaguely recall there might be configuration options for outputting not only the location but also orientation of the stylus? That would also return more values than Brainstorm expects.

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I tried with just two receivers this time. The value sent is still two.
I will check out the outputs set for the stylus.

Hi @ritu
In the left panel that you shared, there is only one value.

Make sure that you disconnect the 3rd receiver from the device.

Yes, when I took the reading above, the third receiver was unplugged.
Even though the first sent command indicates "values sent=2" (initial signal value); following that, subsequent signals are treated as "values sent=initial signal value +1."
It appears to be functioning properly.


I am attaching the screenshot of 3 sent signals.

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