Steve -- Thanks a lot for insightful comments. Best regards -- Julius
Julius Fridriksson Ph.D.
Assistant Professor
Dept. of Communication Sciences & Disorders
University of South Carolina
Tel: (803) 777-5931
Fax: (803) 777-3081
>>> [log in to unmask] 07/20/04 09:12PM >>>
Hi - thanks for sending the data. I think partly this is because your
contrasts are only differential, so you are not picking up the voxels
where the inidivual EVs/stimulus-types are maximal for the
peristimulus
plotting, but where the differential zstats are maximal. Hence you're
not
getting a clear picture of the single-event response. Also I think
it's
not helped by the SNR for these covariates being quite weak. A 0 0 1 0
contrast shows up a reasonable PS plots for EV3.
Anyway - if you really want to investigate the HRF in a more
quantitative
manner you are probably better off using basis functions and using the
found fits rather than looking at the PS plots - hopefully this makes
sense!
Cheers, Steve.
On Mon, 19 Jul 2004, Julius Fridriksson wrote:
> Hi FSLers -- I used a mixed design to collect data for a finger
tapping
> paradigm. The data from the event related and bloced designs were
> analysed seperately in FEAT and the results look great. We were just
> comparing left vs right finger tapping. However, the peri-stimulus
plot
> for the blocked design looks fine but not for the event related
portion.
> I understand that FEAT tries to "guess" what is an event but do not
get
> how it goes about guessing. Any suggestions on what I am doing
wrong?
> That is, how can I analyse the event related data so as to get an
> estimate of the HRF?
> As before, thanks very much for you help. Best regards,
> Julius
> N.B. I used a Gamma function for convolution
>
>
> Julius Fridriksson Ph.D.
> Assistant Professor
> Dept. of Communication Sciences & Disorders
> University of South Carolina
> Tel: (803) 777-5931
> Fax: (803) 777-3081
>
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe 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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