Subject: sparse temporal sampling From: Matt Davis <Matt.Davis@xxxxxxxx> Date: Fri, 15 Jul 2011 08:07:50 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Hi Theresa Here's a few suggestions for analysis of sparse fMRI data. I don't know of a single methods paper that explains everything. You might to read a paper like Hall et al (1999, Human Brain Mapping). Most of the preprocessing and analysis steps are as usual for fMRI data. A few points of difference between sparse and standard fMRI analysis are as follows: 1. Don't perform slice acquisition time correction. Given the 15s delay between scans, interpolation between successive scans is ineffective and will damage your data. 2. At the analysis stage, I often use an FIR basis set of duration 15 seconds (equivalent to your scan repetition rate), with a single time bin. This models the data as a box-car covering the single scan following each condition. This is a simpler model to set up than the typical haemodynamic response model, but usually effective for sparse data. 3. If you do want to use an HRF model - for instance, if you have differences in the timing of trials within your silent period - then you also need to take care over the specification of SPM.xBF.T and SPM.xBF.T0 in your model. 4. You need to take care in specifying the low-pass filter and AR(1) parameters in your model. I often turn these off entirely since my goal is to do second level, group analyses rather than computing single subject statistics. The reason for concern is that scan-to-scan auto-correlation is greatly reduced with a long TR design, and the slow changes in activation between conditions are at a much lower frequency in sparse designs. Good luck! Matt On 15/07/2011 05:06, "AUDITORY automatic digest system" <LISTSERV@xxxxxxxx> wrote: > >Date: Thu, 14 Jul 2011 13:44:23 -0700 >From: theresa veltri <theresaveltri@xxxxxxxx> >Subject: sparse temporal sampling > >Hi, I am currently starting some fMRI analysis in SPM8. Unfortunately I >am >unsure how to account for the sparse temporal sampling design that was >used. >For example, each trial was 15s, but TR is only 4s. Does anyone have expe >rience with specifying such parameters in SPM? Does anyone have any >referen= >ces the could suggest? any help would be appreciated. >Best, > >Theresa Veltri >MSc in Cognitive and Computational Neuroscience >University of Sheffield, UK