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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"

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.The second set of contrast does basically the same thing: [-2 0 1 1 0]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.txt11. 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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