Actually, you can do it either as a simple blocked design where you
specify the timing of each block as described below or as an AB-Blocked
design. If they latter, then you would run mkanalysis-sess with
-designtype abblocked and then use sfa-sess. If you use -designtype
blocked, then you would use selxavg-sess. If you use -designtype blocked
and specify an spmhrf with one derivative, then it will be very similar
to the abblocked.
doug
Jonathan Polimeni wrote:
hi lars,
i just checked with doug, and he agreed that, since your stimulus is
periodic, 'sfa-sess' can do the job provided that you specify that the
analysis should be carried out using a block design.
so, for example, if the TR is 2 sec, and since each of your conditions
lasts 20 TRs per epoch for a total of 10 repetitions (or 20 epochs) per
run, you can define the block design with:
mkblockpar -parname horiz_vs_vert_block.par -TR 2 -nperepoch 20 \
-nepochs 20 -epochid 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2
then define the analysis with something like:
mkanalysis-sess \
-analysis visual_meridian_block -paradigm horiz_vs_vert_block.par \
-designtype blocked -TR 2 -nconditions 2 \
-funcstem fmcsm5 -inorm -mcextreg \
-polyfit 2 -gammafit 2.25 1.25 -taumax 26
(please consult the documentation to determine how to choose the options
on those last two lines.)
the key here is that the design type should be specified as "blocked"
(instead of "retinotopy", which implies phase encoding).
in your case you can use 'sfa-sess', and for this example the command
would be:
sfa-sess -df sesspar -sf sessid -a visual_meridian_block
-jon
On Wed, 27 Jun 2007, Lars Kuchinke wrote:
thanks Jon,
i didn't know that a simple block design analysis is possible to compute the
visual area boundaries...
(which is the reason why I tried to fit it into the standard sfa-sess
analysis)...
could you explain me (shortly) what to do than with my data
regards,
Lars.
-design info: 8hz flickering checkerbords, 20 scans at horizontal meridian, 20
scans vertical..x10 repetitions...
Jonathan Polimeni schrieb:
hi lars,
the FSFast retinotopy analysis stream is geared towards temporal phase
encoded data analysis, which produces field sign maps that can be used to
define area boundaries.
if you opt to use stationary wedge stimuli to activate the horizontal and
vertical meridian representations in visual cortex rather than the
traditional phase encoding stimulus paradigm, since the vertical and
horizontal meridian representations also lie along area boundaries, you
can identify them in your data through a standard block design paradigm
analysis. this is straightforward but outside the retinotopy stream.
instead you can use 'mkanalysis-sess' and 'selxavg3-sess' as described on
the fswiki.
of course it is possible to interpret your periodic stimulus as temporally
phase encoded and run the usual frequency analysis (i.e., 'sfa-sess'), but
i think that the block design analysis is more appropriate for your data.
hope this helps!
-jon
Lars Kuchinke, PhD
Freie Universität Berlin
Allgemeine Psychologie
Habelschwerdter Allee 45
14195 Berlin
[EMAIL PROTECTED]
www.fu-berlin.de/allgpsy
Tel: 030 838 55776
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