Dear Donald,

Thanks for explaining.

But , as I understand from the mailing list (https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1508&L=spm&F=&S=&X=EDD899B9110296EE3B&Y=al-zubaidi%40neuro.uni-luebeck.de&P=468296), with the orthogonalization of PM, that the first PM explain as much variance as possible, then the 2nd PM explain any remaining variance. Now if need to measure the effect of the second order of PM, it will not change when I put in the 1st colum or 3rd column( my case now). Could you give more explain please?

Regarding the RT time, maybe I was not much clear. I already put the RT ( or response time) in the design matrix ( HRF is convolved with the RT and the duration of RT is 0). But here, I mean the difference in time between the stimulus time and the response time ( difference time  = response time - stimulus time) , Because the participants could be  thinking  before  rating the food pictures and that could be changing the amplitude of HRF. Now this time, can I put it as a PM?

Regads,
Arkan


________________________________
M.Sc. Arkan Al-Zubaidi
Klinik für Neurologie
UKSH, Campus Lübeck
Paul-Ehrlich-Strasse 1-3, MGZ
23562 Lübeck
0451 317 9313 14

________________________________________
From: MCLAREN, Donald [[log in to unmask]]
Sent: 21 August 2015 21:55
To: Arkan Al-Zubaidi
Cc: SPM
Subject: Re: [SPM] Changing the order of columns in design matrix reflected to the parametric modulation

(1) The order of columns in the design matrix does not make a difference.

(2) RT should be put in as the duration or as a duration modulator (http://wagerlab.colorado.edu/wiki/doku.php/help/fmri_help/fmri_statistical_models/parametric_modulation)

(3) I would use the mean rating value or mean RT. If you use 0, then it treats that trial as have a rating of 0 or an RT of 0, neither of which are true. Alternatively, you could model those trials as their own trial type.

Best Regards,
Donald McLaren, PhD


On Fri, Aug 21, 2015 at 3:37 PM, Arkan <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Dear SPMers,

II have a block design experiment to measure the functional activation related to the processing of food pictures. The experimental is made up of 2 runs. Each session has 36 blocks. Each block (Each block lasts for 20 seconds) consisted of 2s of food visual stimuli, followed by a 18s resting baseline. In addition, participants were asked to press a button for rating the picture (how much they liked the food in pictures 1-8). Therefore I have a behavior data for each trial. I'm interested about how the behavior across the trials related to the brain activity. To do that I am using a parametric modulation and now this my questions:

1- I used a second order of PM.  And if I understand it correctly this paper (http://www.sciencedirect.com/science/article/pii/S1053811998903512) , they put the most important column of interest in as the first. Is it possible to change the order of the columns in a design matrix in SPM12? I would like to make a first column of the design matrix reflected the second order of PM.

2- I would like to put the reaction time as a PM in the design matrix to make the GLM model more robust and explain everything in my data, is that make sense?

3- In some trails the participants did not rating the picture, Can I put  0  for the missing value in rating or reaction time?




Thanks in advance,

Arkan