Re: extracting timecourse- FIR: block design
Matthew Brett <matthew.brett <at> gmail.com>
2007-01-10 16:48:02 GMT
Hi,
> In my design, I have blocks where there is a single event with a
> specified length 'on' (let's say 50 volumes) and 'off' (let's say 15 volumes
> before and after the 'on' event), so it would look like
> 'off
> 15, on 50, off 15'. [This would constitute 1 complete scanning
> block.....]
>
> I also have much longer blocks where the same event occurs 4 times ( e.g.
> visual flash), for the same length with rest period built in (so it would
> look something like this:
> 'off' 15 vols, ' on 50', off 15 vol, 'on 50', off 15 vol, on 50,
> off 15, on 50, off 15
>
> [This would also constitute 1
> complete scanning block.....]
>
> What I'd like to do is look at the timecourse for a given ROI active across
> all block types, meaning my short and long blocks. To find the FIR for the
> short blocks by themselves, inputting a bin length is straightforward as I
> only need to have enough bins to account for the 'on period'. But to do the
> same for either the long blocks by themselves OR all blocks put together,
> inputting the bin length is where I get stuck, as I do NOT want to average
> the rest periods between each 'on' event when looking at the timecourse of
> 'on' activation for this ROI. So my question is if there is some way to
> input the when & the bin length of my 'on' events using MarsBar....without
> including the rest periods.
If this is an FMRI design then the FIR is usually used to include the
time for the HRF to return to zero - say about 25 seconds. So, the
standard way would be to give a bin length * number of bins adding up
to 50 * the TR plus 25 seconds. In this case, for the multiple event
runs, you probably don't have any extra rest against which to estimate
the baseline, so the baseline will be fairly arbitrary, but you should
be able to estimate the shape of the response nevertheless.
Best,
Matthew
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys - and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
RSS Feed