[Eeglablist] Shifted rejection boundaries in continuous data

[Makoto Miyakoshi]

Dear Maria,

I could not replicate the phenomenon you reported. If you don't mind,
could you send us a piece of your data to replicate it? Please email
me separately. mmiyakoshi at ucsd.edu

James, your experiment with EEGLAB is excellent. That gave me a good
initial guess.

Makoto

2012/11/21 Maria Teresa Wijaya <a0089301 at nus.edu.sg>:
> Hi James,
>
> I did everything using the GUI: plot > channel data (scroll) > drag and
> click to specify the boundaries > reject button > save it as file . In my
> case, my events seem to still be in the right place when I tried using
> eeg_eegrej function with overlapping boundaries.
>
> Maria
>
>
>
> On Wednesday 21,November,2012 11:41 AM, James Desjardins wrote:
>>
>> Hi Maria,
>>
>> What were the exact functions or menu items that you used to select the
>> periods for rejection?
>>
>> Similarly, what exactly did you use to remove the periods?
>>
>> I am interested in this problem because I have caused such things to
>> happen while tinkering with the EEG structure from the command line. The
>> shifting of events from their true position relative to the data can occur
>> if there is overlap among the latency boundaries specified for removal in a
>> call to the eeg_eegrej function, but I have never seen it happen while
>> building latency boundaries or removing continuous data periods using the
>> EEGLab GUI.
>>
>> For example, If I specify overlapping latency boundaries:
>>
>> rejarr=[10000 11000;10900 11900];
>>
>> Then try to remove both of them with one call to eeg_eegrej:
>>
>> EEG = eeg_eegrej(EEG, rejarr);
>>
>> I find that all of the events following the rejection period are shifted
>> to the left (relative to their true position) in the data scroll (with the
>> shift distance being equal to the duration of the overlap across the rejarr
>> latency boundaries).
>>
>> If you are building latency boundaries outside of the EEGLab GUI and using
>> eeg_eegrej to purge them it is crucial that you merge the overlapping
>> latency boundaries.
>>
>> Again, I am very interested in this topic. I look forward to exploring
>> this further if you have more to add.
>>
>>
>> James
>>
>> ________________________________________
>> From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu]
>> on behalf of Maria Teresa Wijaya [a0089301 at nus.edu.sg]
>> Sent: November-18-12 11:07 PM
>> To: mmiyakoshi at ucsd.edu
>> Cc: eeglablist at sccn.ucsd.edu
>> Subject: Re: [Eeglablist] Shifted rejection boundaries in continuous data
>>
>> Dear Makoto,
>>
>> I recorded my data using Biosemi Active two system with 64 electrodes at
>> 256Hz. Data were band pass filtered at 0.1-20 Hz and re-referenced
>> offline first to nose reference to remove bad channels. Removed channels
>> were interpolated and the data were re-referenced to average reference.
>> I then checked the continuous data for non-typical artifacts, removed
>> them, and saved the data with a new name. The shifted rejection
>> boundaries problem appeared in this new data set.
>>
>> Kindly let me know if I need to provide any other information.
>>
>> Thank you.
>>
>> Regards,
>> Maria
>>
>>
>>
>> On Saturday 17,November,2012 01:33 PM, Makoto Miyakoshi wrote:
>>
>>>
>>> Dear Maria,
>>>
>>> We need more information to identify what caused this.
>>> Could you tell me more detail?
>>>
>>> Makoto
>>>
>>> 2012/11/12 Maria Teresa Wijaya<a0089301 at nus.edu.sg>:
>>>
>>>
>>>>
>>>> Dear list,
>>>>
>>>> I did rejection on continuous data and noticed that the rejection
>>>> boundaries shifted from where they are supposed to be (picture here:
>>>> http://www.flickr.com/photos/89964745@N02/8178303896/in/photostream).
>>>> This happened to several of my subjects, and it also happened to someone
>>>> else in our lab before. My questions are:
>>>>
>>>> - What are the possible reasons of this shift?
>>>> - Is there any way I can know if any of my event triggers have also been
>>>> shifted or if only the rejection boundaries are shifted?
>>>>
>>>> Thank you for your help.
>>>>
>>>> Regards,
>>>> Maria
>>>> _______________________________________________
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>>>
>>>
>>>
>>>
>>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego