AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

History of AFNI updates  

|
October 31, 2005 05:23PM
Yes, conjunction analysis with 2 contrasts can be done with the following expression in 3dcalc:

-expr 'step(a-a_threshold) + 2*step(b-b_threshold) + 4*step (-a_threshold-a) + 8*step (-b_threshold-b)'

And the resulting map can be interpreted as the following:

0: no activation and no deactivation;
1: activation in condition 1 only;
2: activation in condition 2 only;
3: activation in both conditions;
4: deactivation in condition 1 only;
6: activation in condition 2 and deactivation in condition 1;
8: deactivation in condition 2 only;
9: activation in condition 1 and deactivation in condition 2;
12: deactivation in both conditions.

However if you don't want to differentiate activation and deactivation, the expression can be simplified as:

-expr 'astep(a, a_threshold) + 2*astep(b, b_threshold)'

The definition of step and astep is:

step(x) = {1 if x>0 , 0 if x<=0},
astep(x,y) = {1 if abs(x) > y , 0 otherwise} = step(abs(x)-y)


Gang
Subject Author Posted

Conjunction/Difference analysis

Hedvig September 13, 2005 03:45PM

Re: Conjunction/Difference analysis

Gang Chen September 13, 2005 05:14PM

Re: Conjunction/Difference analysis

Hedvig September 13, 2005 05:58PM

Re: Conjunction/Difference analysis

Gang Chen September 14, 2005 01:16PM

Re: Conjunction/Difference analysis

Hedvig September 14, 2005 04:24PM

Re: Conjunction/Difference analysis

Hedvig September 14, 2005 05:34PM

Re: Conjunction/Difference analysis

Gang Chen September 14, 2005 05:58PM

Re: Conjunction/Difference analysis

Hedvig September 15, 2005 11:09AM

Re: Conjunction/Difference analysis

nadine October 31, 2005 03:32PM

Re: Conjunction/Difference analysis

Gang Chen October 31, 2005 03:44PM

Re: Conjunction/Difference analysis

nadine October 31, 2005 04:58PM

Re: Conjunction/Difference analysis

Gang Chen October 31, 2005 05:23PM