Hi
High-pass filtering somewhat skews the beginning and the end of the
design - this is not a problem as in Feat the same high-pass filter
is applied to the design and the data, i.e. both should see the same
degree of skew. You can check the effect of the filter in the Feat
gui by simply setting 'total volumes' to some number and then
playing around with different setting of the filter - if you have the
'full model setup' window open simply press 'View design' each time
you change the setting and see what happens.
Hope this helps
Christian
On 1 Aug 2007, at 03:34, Daniel Wolf wrote:
> I'm not sure if this is relevant, but I've noticed that applying high
> pass temporal filtering to EVs sometimes produces strange dips at the
> beginning in the resulting design matrix columns...could high pass
> filtering do this to the initial timepoints of the functional data?
> Dan
>
>
> On 7/31/07, Vishwadeep Ahluwalia <[log in to unmask]> wrote:
>> Hi,
>> I plotted the mean time series extracted from filtered_func image
>> within
>> different ROIs and found that the first two values of each time
>> series is
>> way less than the consequent values. I'm assuming this is done on
>> purpose
>> and is not an artifact. Can anyone tell me why this is done and what
>> pre-processing step causes this decrease? Thanks!
>> -Vish
>>
____
Christian F. Beckmann
University Research Lecturer
Oxford University Centre for Functional MRI of the Brain (FMRIB)
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
[log in to unmask] http://www.fmrib.ox.ac.uk/~beckmann
tel: +44 1865 222551 fax: +44 1865 222717
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