Dear Jing,
Do you still get this shift without any filtering (just with baseline
correction)? If you do I might need to look at an example of you raw
data file.
Best,
Vladimir
On Mon, Jun 20, 2011 at 2:16 PM, Jing Kan <[log in to unmask]> wrote:
> Hi Panagiotis,
>
> Thanks for your reply!
>
> I know that the downsampling of SPM will truly generate some error shift
> of the signal in some cases as you said. However, I avoid to use the
> downsampling data here but directly using the raw data, this error-shift
> problem still exist.
>
> My data is from Elekta 306 system. I also did the preprocessing with the
> Elekta software. It shows the response occur at 2.7 ms after stimulus
> which sounds much reasonable than occur at -7 ms by SPM. I have no idea
> what else I can do to solve this problem.
>
> I will be really appreciate of any of the clues.
>
> Many thanks,
>
> Jing
>
>
>> Hi Jing,
>>
>> Just a thought...
>>
>> Did you downsample a continuous file before epoching? I have noticed
>> that if I downsample a continuous (CTF-MEG) file after filtering and
>> before epoching, the triggers shift in a weird way (up to +/-10ms) even
>> if he downsampling rate is very close to the original one... (I mean,
>> you expect a reasonable jitter in the triggers if you go from 1000Hz to
>> 200Hz, but not +/-10ms if you go from 1000Hz to 950Hz for example). I
>> wanted to investigate this issue further and provide a proper report but
>> I did not have the time to do it yet... and maybe I got something else
>> wrong.
>>
>> Anywayz,
>> Good Luck :)
>>
>>
>>
>> On 6/20/2011 11:45 AM, Jing Kan wrote:
>>> Dear SPMers,
>>>
>>> Thanks for your concern!
>>>
>>> I am dealing with the MEG data pre-processing. After the steps of
>>> filter,
>>> epoch, artifact detect, averaging and baseline checking, I realized the
>>> response shifted a few seconds, i.e. the strong response occurred after
>>> the stimulus shifted into 7 ms before the stimulus.
>>>
>>> May I ask is anyone know the reason about this?
>>>
>>> Many thanks in advance!
>>>
>>> Jing
>>
>>
>> --
>> Panagiotis S. Tsiatsis
>> Max Planck Institute for Biogical Cybernetics
>> Cognitive NeuroImaging Group
>> Tuebingen, Germany
>>
>
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