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openyou / emokit

Open source driver for accessing raw data from the Emotiv EPOC EEG headset
http://www.openyou.org
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Where are the reference sensors? #78

Closed nh2 closed 11 years ago

nh2 commented 11 years ago

I realized that the sensor map from Emotiv has 16 sensors displayed, while the emokit code only uses 14.

The EPOC has 18 electrodes; it looks like 14 of them are used as sensors, and 4 of them are reference points. Of those, most people seem to enclose 2 of those reference points with the rubber pads.

Is it possible to get the quality of the sensor nodes out of the stream (Emotiv's map seems to do this)?

ghost commented 11 years ago

The sensors that are covered are in the same wiring lead as the ones that are not from what I gather.

Yeah that's already in the code.

From: Niklas Hambüchen [mailto:notifications@github.com] Sent: Wednesday, May 08, 2013 8:55 AM To: openyou/emokit Subject: [emokit] Where are the reference sensors? (#78)

I realized that the sensor map from Emotiv has 16 sensors displayed, while the emokit code only uses 14.

The EPOC has 18 electrodes; it looks like 14 of them are used as sensors, and 4 of them are reference points. Of those, most people seem to enclose 2 of those reference points with the rubber pads.

Is it possible to get the quality of the sensor nodes out of the stream (Emotiv's map seems to do this)?

— Reply to this email directly or view it on GitHubhttps://github.com/openyou/emokit/issues/78.

nh2 commented 11 years ago

Sorry, I do not entirely understand what you mean. Which ones are in the same wiring with what? I'd not be surprised for all reference sensors being transmitted as one, but that would still be one more thatn 14 ...

wmvanvliet commented 11 years ago

epoc

The EPOC has 4 'slots' for reference electrodes. In order to perform a recording, you must place electrodes in at least 2 of them. This means you can either use the bottom ones marked in red in the picture, or the top ones marked in green.

Whether you use the 'top' or the 'bottom' positions for the reference electrodes makes no difference in the sensor map, as both positions are mapped to the same indicators in the sensor map.

Electric potential (voltage) is always measured as a difference between two points, in this case as the difference between each of the 14 electrodes and the average of the two reference electrodes. This means 14 data channels are available, even though 16 electrodes are attached.

nh2 commented 11 years ago

@wmvanvliet Thanks! The picture is especially helpful.

nh2 commented 11 years ago

@wmvanvliet Actually, this isn't entirely clear yet. Could it be that what you marked with green are not reference electrodes? Looking at this map:

Head map

It looks like the the four contacts in the front are all real electrodes.

Is it possible that the the other pair of reference electrodes are actually the ones visible above the Emotiv logo?

wmvanvliet commented 11 years ago

@nh2 You are absolutely right. I've modified the image accordingly.

nh2 commented 11 years ago

Awesome, thank you.