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Hi Claus & SPMers - thanks for pointing that out. You were correct.

After fixing this I realized that there are a couple of mistakes in the  "README_GLM_PPI.txt" http://www.fil.ion.ucl.ac.uk/~wpenny/datasets/attention/README_GLM_PPI.txt for the practice dataset. For example, I believe that there are actually 4 conditions, but it is written as though there are only three (see examples below)

Specifically, here are the other problems that I found with
the "README_GLM_PPI.txt"

  1. The text instructs you to specify the contrast [0 0 -1 1 0]. There are two things wrong with this, one, this is the problematic contrast that prompted this message. Two, you cannot specify 5 contrast codes for an SPM that only has 4 conditions. Experienced users know this, but as it is a practice data set I bet this trips people up.
  2. The second set of contrast does basically the same thing: [-2 0 1 1 0]
  3. And finally the point listed above, that there are four conditions but the instructions repeat "condition 3" twice making it quite confusing.

Thanks again!
Shaqunada

ORIGINAL TEXT - http://www.fil.ion.ucl.ac.uk/~wpenny/datasets/attention/README_GLM_PPI.txt
11. Number of conditions [4]
12. Name for condition 1 [Fixation]
13. vector of onsets - Fixation [fix_index]
13. duration[s] (events=0) [0]
14. Parametric modulation [None]
15. Name for condition 2 [Stationary]
16. vector of onsets - Stationary [stat_index]
17. duration[s] (events=0) [0]
18. Parametric modulation [None]
19. Name for condition 3 [NoAttMot]
20. vector of onsets - NoAttMot [natt_index]
21. duration[s] (events=0) [0]
22. Parametric modulation [None]
23. Name for condition 3 [AttMot]
24. vector of onsets - AttMot [att_index]
25. duration[s] (events=0) [0]
26. Parametric modulation [None]
27.
User specified [0]


MODIFIED TEXT

12. Name for condition 1 [Fixation]
13. vector of onsets - Fixation [fix_index]
13. duration[s] (events=0) [0]
14. Parametric modulation [None]

15. Name for condition 2 [Stationary]
16. vector of onsets - Stationary [stat_index]
17. duration[s] (events=0) [0]
18. Parametric modulation [None]

19. Name for condition 3 [NoAttMot]
20. vector of onsets - NoAttMot [natt_index]
21. duration[s] (events=0) [0]
22. Parametric modulation [None]

23. Name for condition 4 [AttMot]
24. vector of onsets - AttMot [att_index]
25. duration[s] (events=0) [0]
26. Parametric modulation [None]
27. User specified [0]


----- Original Message ----
From: Claus Lamm <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, February 21, 2008 4:34:28 PM
Subject: Re: [SPM] Nonsensical results from sample SPM5 data set. What are we doing wrong?

Your contrast looks wrong - seems like you are comparing the constant (+1,
last column) against the 3rd column (-1)
You probably should use something like a [1 0 0 0] to assess the PPI

Hth
C


************
Dr. Claus Lamm
Research Associate

Social Cognitive Neuroscience
Department of Psychology
The University of Chicago

5848 S. University Avenue, Chicago, IL 60637
Phone: (773) 702-4661  Fax: (773) 702-0886

EMail: [log in to unmask]
Web: http://scnl.org/claus.html



-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On
Behalf Of Shaquanda Jones
Sent: Thursday, February 21, 2008 3:25 PM
To: [log in to unmask]
Subject: [SPM] Nonsensical results from sample SPM5 data set. What are we
doing wrong?

Dear SPMers,

We have been playing around with the sample SPM data set available here
(attention to visual motion):

http://www.fil.ion.ucl.ac.uk/~wpenny/datasets/attention.html

We have analyzed the results using the directions listed in the
"README_GLM_PPI.txt" data set (using the updated SPM5), but as you can see
by the screen shot, we are obviously getting results that do not make sense
(i.e. t values in the hundreds). We are probably doing some thing simple
wrong, but it is not obvious to us yet what that is. Any suggestions would
be much appreciated.

Sincerely,
Shaqunada

Nonsensical results from sample SPM5 data set. What are we doing wrong?





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