Thank you Jason for the paper. It is really useful for pepole that 
investigate the human olfatory system by using fMRI. However, the paper 
mainly focuses on the optimization of both stimulation timing and data 
analyses within block desings. Block desings are not a suited alternative 
for the aims of my study.

My concerns pertain to the implementation of event related desings with 
long SOA. So any other suggestion about this topic is welcome.

Federico.

       


Dear Federico,
We have addressed all of these questions in our paper, even how to time the 
breathing so subjects are inhaling the odors most efficiently during the 
stimulus period.

I hope this helps,
Jason.

(I apologize for the double post, I hit the wrong key and accidentally sent 
the email before finishing!)



Matthias H. Tabert, Jason Steffener, Mark W. Albers, David W. Kern, Maria 
Michael, Haiying Tang, Truman R. Brown, Davangere P. Devanand, Validation 
and optimization of statistical approaches for modeling odorant-induced 
fMRI signal changes in olfactory-related brain areas, NeuroImageVolume 34, 
Issue 4, , 15 February 2007, Pages 1375-1390.
(http://www.sciencedirect.com/science/article/B6WNP-4MNYJW0-
4/1/9c4fe1c0ee2e59b11dae6f728f526e6c)


----- Original Message ----
From: Federico Tubaldi <[log in to unmask]>
To: [log in to unmask]
Sent: Tuesday, April 15, 2008 8:54:47 AM
Subject: [SPM] optimizing experimental designs with long SOA

Dear Experts,

I am planning an experimental design aiming at the investigation of bold 
response evoked by identification of odor stimuli. Recent literature 
pertaining to this topic suggests to use an event related design with long 
SOA. According to this literature, if an odor stimulus is delivered for 3 
sec. under two different experimental conditions, A and B, and I am 
interest in the activity elicited by the odor for A than B condition, then 
I have to implement the following experimental design.

Odor stimulus condition A, duration = 3 sec.
SOA = 10 sec.
Odor stimulus condition B, duration = 3 sec.
SOA = 10 sec.
...
Odor stimulus condition A, duration = 3 sec.
SOA = 10 sec.
Odor stimulus condition B, duration = 3 sec.

After I will perform the t-contrast: odor stimulus condition A  > odor 
stimulus condition B.

For reasons that concern the human olfactory system and my experimental 
task (odor identification), I cannot reduce the SOA.

Now the questions are:
1)Does this experimental design have sufficient power to detect the effect 
of my interest (i.e., A > B)?
2)If I increase stimulus duration from 3 sec. to 6 sec., does the design
power increase?   
3)Should I use a variable (e.g., 10+/- 5 sec) than a fixed (e.g., 10 sec.) 
SOA duration so as increase the design power? 

Many thanks in advance.

Federico.

Federico Tubaldi, Ph.D Student
Dept. of General Psychology
University of Padova, Via Venezia 8, 35131, Padova, Italy Present working 
position:
Visiting student at the Dept. of Neuroradiology University of Tuebingen, 
Hoppe-Seyler Strasse 3, D-72076, Tuebingen, Germany
email: [log in to unmask]
mobile: 0049 0177 7466815
mobile: 0039 335 1400451