Hi - how the FIRs look depends on the interaction between individual
FIR impulse duration, TR and input stimulus timings (onset and
duration). The window length is probably enough - what you're seeing
is most likely just a combination of those timing factors.
Cheers.
On 5 May 2007, at 09:22, Junghee Lee wrote:
> HI
>
> Thanks a lot for reply. I do have another related question. When
> I tried a window of 14 seconds, the hemodynamic functions of 4 EVs
> look physiologically plausible. However, when I tried a window of
> 12 seconds, the hemodynamic functions of 3 EVs did not look right
> (the one EV looked a little better than others). I wasn't sure
> whether the FIR impulse is sensitive to the window length. Is this
> because I didn't have enough time window to cover the hemodynamic
> rise and fall time?
>
> Thanks,
> Junghee
>
>
> On May 5, 2007, at 12:10 AM, Steve Smith wrote:
>
>> The window length is divided by the number of FIR impulses that
>> you ask for so that each impulse has duration length/number seconds.
>> A common approach is to organise that so that the length covers
>> the normal haemodynamic rise and fall time (eg 15 seconds) and set
>> the number so that each is one TR in duration.
>> Cheers.
>>
>>
>> On 4 May 2007, at 23:16, Junghee Lee wrote:
>>
>>> Hello Everyone,
>>> I have a question of using FIR basis function. We used a fast
>>> event-related design (TR=2) and there are 4 EVs. I would like
>>> to compare a window of 12 seconds and a window of 14 seconds.
>>>
>>> I'm not sure whether I understand what "number" means exactly. Is
>>> this number of FIR basis functions? If so, is there any optimal
>>> number of functions I should use?
>>>
>>> Thanks a lot!
>>> Junghee
>>
>>
>> ---------------------------------------------------------------------
>> ------
>> Stephen M. Smith, Professor of Biomedical Engineering
>> Associate Director, Oxford University FMRIB Centre
>>
>> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>> +44 (0) 1865 222726 (fax 222717)
>> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
>> ---------------------------------------------------------------------
>> ------
>>
>>
> ------------------------------------
> Junghee Lee
> Post-doctoral fellow
> Semel Institute of Neuroscience and Hunan Behavior, UCLA
>
> Phone: 310-478-3711 ext.42986
> email:[log in to unmask]
> Mail: UCLA/VA Greater Los Angeles Healthcare System
> 11301 Wilshire Blvd.
> MIRECC, Bldg. 210 (MC 210A)
> Los Angeles, CA 90073
> Web:http://greenlab.npih.ucla.edu or
> http://www.psy.vanderbilt.edu/students/leej11
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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