Number of events 0 about eeg-expy

[oreHGA]

By visual inspection I do not see any differences between my experimental data file and that of example data (except that I only recorded a single run of 120s, while example data had 6 runs all of longer duration).

@Maari13, ran through your file locally and this seems to be the reason why you're not getting events returned.

In the notebook, you'd notice that this snippet exists:

events = find_events(raw)
event_id = {'Non-Target': 1, 'Target': 2}
epochs = Epochs(raw, events=events, event_id=event_id,
                tmin=-0.1, tmax=0.8, baseline=None,                                                                                  
                reject={'eeg': 100e-6}, preload=True,                                                                                  
                verbose=False, picks=[0,1,2,3])

print('sample drop %: ', (1 - len(epochs.events)/len(events)) * 100)

epochs

The reject field determines the threshold for rejecting epochs based on peak-to-peak signal amplitude. See MNE docs here

Notice below how changing the reject value to a much higher number keeps more events but potentially including more noisy results.

NB: EEG is quite noisy by default, even minor blinks & muscle movements can be responsible for spikes in data, causing the events to be filtered out when reject is applied

My recommendation here would be

• doing a much longer recording maybe 5mins
• ensure that electrodes are well placed to ensure good quality recording
• tweaking reject value iteratively

cc @JohnGriffiths & @ErikBjare if they have any other ideas that could help here

[JohnGriffiths]

Thank you @oreHGA - indeed this is not an uncommon issue. As Ore said, you can try tweaking the threshold iteratively; e.g. up/down a few percent. You will probably see as you do that more epochs are kept the more lenient you go, and concurrently that the average ERP trace gets noisier ('wigglier'), because more noisy data points are being included.

As Ore said, the fundamental issue here is a noisy recording set up.

Try using the muselsl signal viewer to confirm you have good signal before running the experiment

muselsl view -v 2

(you may have to also pip install vispy first )

And make sure the numbers on the right are <20. Then kill the viewer and run the eegnb expt.

We have nearly finished a simple signal quality check function for eeg notebooks that will help with this part of the setup process. Watch this space (or watch the PRs if you're very interested).

Let us know if this helps!

[Maari13]

Thank you so much for the explanation and advice. It did not occur to me that an automatic quality check was applied to the epoch data. I was going to do longer recordings, but first wanted to make sure I got things to work and then was puzzled ... I will definitely need to check the contact of the electrodes with the scalp and preview the signal before acquiring data next time. And then tweek the reject value

[oreHGA]

Hi @Maari13 , hope you were able to get more sample in after adjusting the "reject" threshold. I'll go ahead and close this now but feel free to reply to the thread if you still have any issues. Cheers