Dear Susan,
your setup with silence periods between each scan is indeed tricky. If
your experiment can be modelled as a block design, I would go for
- no slice timing correction
- model TR as 3000 ms
- model blocks with onsets and duration
If you really need to model the design event-related, then you should
enter TA as 1.55 secs and TR as 3.0 secs. For modelling, your TR would be
3 seconds, and you have to set your reference time bin in a way that it
corresponds to the time when your reference slice was taken.
hope this helps,
Volkmar
On Fri, 21 Sep 2007, Susan L. SHUAI wrote:
> Dear SPMers,
>
> I am just a new comer to use SPM and doing fMRI experiment. I have
> encountered much difficulty in analyzing the data now. My experiment
> design is a block design and the acquisition is a cluster acquisition
> because it will allow for silence to present auditory stimulus.
>
> Should I follow the Event-related analysis? In slice timing, what should I
> put as TA? Is it the start time of the last slice acquisition? For
> example, I have 32 slices, and they are acquired in 1.6s. Is the TA 1.55?
>
> In the original experiment, I did the continuous acquisition and the TR is
> 2000ms. In the cluster acquisition, the TR is 3000ms and TD is 1400ms
> allowing for silence. But the analyzed results are very different. In the
> first case, most contrasts show significant differences, while in the
> second case, little contrasts show differences.
>
> I think the slice order and reference slice are all set right. What would
> be the reason for such large differences? How can I check my analyze
> result? I am feeling desperate about the situation now.
>
> Thank you for your help!!
>
> Regards,
> Susan
>
--
Volkmar Glauche
-
Department of Neurology [log in to unmask]
Universitaetsklinikum Freiburg Phone 49(0)761-270-5331
Breisacher Str. 64 Fax 49(0)761-270-5416
79106 Freiburg http://fbi.uniklinik-freiburg.de/
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