after opening eyes, time lag until alpha extinguished

calvin844calvin844
edited February 2016 in Software
I really need your help.

I use 

32bit Board Kit (8-channel), win 7, notebook


I am using processing and modify shark program by Chip which can measures alpha wave

The problem is:
When running the program, there is time lag which mean

In the brain
when i close my eyes, there is alpha wave. 
when i open my eyes, there is no alpha wave.
In my measurement,  when i open my eye, the computer still detect alpha wave due to alpha wave detected within time lag about 1 second 

What i have tried but still not work:
I have to do a real time measurement instead of saving SD card
I can't change the buffersize (but i dun;t know where to change it )

What I need:
the processing is at the same step as the data streaming from openbci

What I compromise:
1. can I reduce data streaming so that reduce the workload of the the processing?
2. or other possible solution 

really thanks for your help .

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited February 2016
    Calvin, you are on Windows, so you use the Windows control panel to change the latency setting.

    http://openbci.com/forum/index.php?p=/discussion/200/latency-timer-windows-control-panel-setting

    The link you mentioned is for Mac users.

    re: slight delay upon opening eyes before alpha extinguishes: this may be just normal physiology for the person you are measuring. For example with myself, I've done a lot of Zen style open eye meditation. So I have
    some alpha present even with my eyes open.

    re: Processing workload. Your modern Win7 notebook should have plenty of CPU cycles to run the GUI app.

    William

  • calvin844calvin844
    thanks 

    (this is a just a example brain strom)May i know is it possible to stop the music playing by measuring the absence of alpha wave .When i hear some specific note and i open the eye to stop the music. I find that the "time lag" or "remaining alpha wave" can't make it work. Any solution can be used? 

    calvin


  • wjcroftwjcroft Mount Shasta, CA
    Could you try your experiment with another friend and see if the lag is different or disappears?

    As mentioned previously, your personal alpha generation may be laggy like this. Nothing is likely wrong either with your equipment or your physiology.

  • calvin844calvin844
    I have tried the experiment with 2 friends . I find that  we need 2 seconds for all alpha waves to disappear . And I observe that if I hit the the electrode sticking on the back of my head. I find the signal shown on the screen a little dalay . So I just wonder if the delay is caused from the hardware.


  • wjcroftwjcroft Mount Shasta, CA
    edited February 2016
    The hardware is sending samples at 250 sps, 4 milliseconds per sample. So there could be a few sample times delay before the data is available at the app. The Processing GUI app only does so many frame updates per second. (I recall about 10 fps). There are digital filter and FFT delays before those graphs can update on the screen; this is inherent in DSP digital signal processing. The raw channels update faster than the FFT graph.

    If you look at the larger world of BCI, other techniques such as SSVEP or P300 are used if you want more precision. But even in that case, signals are naturally laggy and noisy.

  • biomurphbiomurph Brooklyn, NY
    It may be possible to use the eye blink artifact to trigger your 'off' signal.
    Is there enough of an EMG artifact from frontal lobe electrodes to do that?
  • calvin844calvin844
    edited March 2016
    Thanks all

    These are our final product and also posted in general discussion

    using openbci + arduino and app inventor to control mobile phone 

    hope to help the patients using brainwaves for playing music and radio , make a phone call and switch the light on and off

    The link will show how it works 


    Thanks
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