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n_Forcer · Joined: Nov 11, 2014 Posts: 5

Hi there,

i use a Contec KT88-1016 device with bioera for Neurofeedback and have some questions.

1. I have a lot of 50 HZ noise in my signal. If i use a lowpass-filter e.g. < 35 hz and connect it to a osciloscope the raw-signal looks very good. Also i use a FFT-Transform -> 3D Vector display and see the 50 HZ noise in the raw signal.
Let?s say i do SMR reward training with an bandpassfilter 12-15 HZ, should i use a lowpass filter before the bandpassfilter, to filter the 50 hz noise out? Or should the bandpassfilter be enough to get a good training-signal? When i connect the bandpass filter to a osciloscope the signal looks good to me, but im not an expert.

2. When i use more then one filter, thers a filter order in the propertys. The standard value is 4. So is the first filter a 4 and the second 5, and so on... Or can i use 1,2,3 an so on?

3. In the next time i want to use coherence training with bioera. Therefore thers the bh_coherence object. Lets say i connect Ch1 and Ch2 to the coherence object, must i use a filter for the coherence HZ-range between the channels and the coherence-object? I ask, because in the propertys of the bh-coherence object theres a low and high frequency field. I think when i set this propertys i don?t need a filter between, is that right?

Thanks for answering my questions :-)

jarek · Joined: Oct 22, 2007 Posts: 1073

1. Only bandbass filter should be enough and in fact better. It is important that the signal is not saturated because of the 50Hz noise. Pre-filtering (like notch) makes sense only if done on the device (if the device has such option, I don't believe kt88 does).

2. Higher filter order increases the filter response time (bad) but make the filter more steep (good). So you need to make a decision what is more important.

3. When I trained Alpha coherence I was adding Alpha filter before the coherence element. The Coherence element's range is done using FFT (take the bins in the alpha range and discard the rest), it has no normal filters. The effect should be similar, but it is not the same. If you do not use input Alpha (or other bandpass) filters, then you should use a low pass filters in this case (for example <45), one for each channel.

n_Forcer · Joined: Nov 11, 2014 Posts: 5

Let?s say i wan?t to train two coherence values at the same time (e.g. SMR and Gamma Coherence up).

So i would connect Channel 1 with a SMR and Gamma Bandpassfilter. The same for Channel 2. Then i implement 2 Coherence nested-designs and connected the filters to them (Channel 1 SMR and Gamma Filter to coherence object 1 and for Channel 2 the same to the coherence 2 object).

In the next step i implent 2 threshold objects, which are connected to the coherence objects. I read in another post, that the output from the coherence object is between 0 to 1. So i set the threshold > 0.5 digit or > 50%.

At the end of the design i connect the two thresholds to a logical AND Mixer and from there to the feedback object (e.g. Route Game).

Is this procedure correct, to train two coherence values up or down?

You write in your answer to me, that the coherence object use FFT and take the bins in the alpha range and discard the rest.
So if i train e.g. SMR coherence, must i set the bandwith value in the coherence object preferences to 12-15 HZ? Because if i let the standard value at 8 -12 HZ, the output from the connected SMR-Bandpassfilter would be discard. Is that right?

The output from the Bandpassfilter is a scalar value. Can i connect this directly to the bh_coherence object? Because this have a float input. Or must i set a ScalarToFloat object bewtween the filter and the coherence object?

jarek · Joined: Oct 22, 2007 Posts: 1073

Yes, 2 bandpass filters for each range (SMR and Gamma) and 2 coherence nested designs.

In general, I prefer to use Float elements. So I would use float Filter, which can be directly connected to the coherence object. And use ScalarToFloat to connect KT88 to it (it will be automatically added inside connection if you try to connect Scalar output pin with Float input pin, the connection will have different color in such case).

Yes, the coherence output value is between 0.0 to 1.0. The threshold can be anything, not just 0.5, it might be a good idea to make it adjustable (for example with a slider) to see what works. I personally only used continuous tone as feedback (no thresholds), so I can't really say what can be the best here.

Yes, with bandpass filters before Coherence element, you do not need to set the frequency range values in the Coherence element properties (set them to 0 and 50).

n_Forcer · Joined: Nov 11, 2014 Posts: 5

Continuous tone as feedback seems very interesting to me. I look at the OneRewardContinuousTone example.

If i use this feedback in my coherence session, i can set the range mapper object to digit between 0.0 and 1.0. So the tone adjust to the output from my coherence objects. Is that right?

jarek · Joined: Oct 22, 2007 Posts: 1073

Yes, that is exactly what I was doing.