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.


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,

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