You want the SPM.Sess(s).P field. the numbers can be anything, 1 for each onset vector. However, this only will work for each onset of a regressor, not TR. Modulating each TR doesn't really make sense from the point of a GLM.

Cheers,
Michael

On Tue, Jul 26, 2011 at 1:48 PM, Watson, Christopher <[log in to unmask]> wrote:
Are you talking about doing parametric modulations? What's your task?
________________________________________
From: SPM (Statistical Parametric Mapping) [[log in to unmask]] On Behalf Of Cinly Ooi [[log in to unmask]]
Sent: Tuesday, July 26, 2011 3:28 PM
To: [log in to unmask]
Subject: [SPM] Varying the weight for 1st level design matrix

Dear All,

Someone asked me to run a first level analysis where instead of a standard boxcar or event design, I have a weighting value associated with each TR. I believe what I have to do is to set the onset time and duration as usual, then assign a weight to each onset time.i.e., instead of accepting the standard weight of '1,1,1,1', I want to specify them as '2,1,1,2' for example.

Since each session will have its own unique weights, for ease of data entry, I will be reading the weights from files and will be processing the data using Rhodri's AA.

A bit of digging into AA shows that  I have to setup this up using SPM.Session(s), and I believe SPM.Session(s).U is the candidate to accept the weights. My problem is, after reading spm_FMRI_design.m, I still have no clue how to set the weight.

How do I go about setting the weights? These weights are expected to be convoluted with HRF later.

In case it helps, it is one weight per volume. So since I have 224 volumes in the fMRI time series, I will have 224 weights to put in.

Many thanks in advance and hope to hear from you soon.

Best Regards,
Cinly



--
Research Associate
Gazzaley Lab
Department of Neurology
University of California, San Francisco