Hi, much thanks in advance for your assistance.

I have some basic questions about setting up gltCode tests in 3dLME and interpreting them. I’ve tried most of these things out (except Q5), and things seem to be working. I just want to make sure, though, that I’m not doing anything incorrectly, given that I can’t find the answers to these questions online.

]Background. I’m using a fully-crossed balanced design with no missing data of the form A x B X C. A is a group variable with 2 levels, A1 and A2 (20 participants at each level). B and C are repeated measures, each with two levels, B1 and B2, and C1 and C2, respectively.

The output that I’m getting for this design from 3dLME shows F briks for each main effect and interaction, and for the intercept. Nothing else.

Q1. When I add gltCode contrasts, I obtain a z brik and an unlabeled brik. I assume contains betas (looks like betas)? This is all fine, but I had been expecting a t brik, not a z brik. I just want to make sure that this is ok, and if so, I’d like to better understand why a z brik has been generated and not a t brik. Is there a brief reason?

Q2. I would like to obtain z briks for each level of each factor in the design (e.g., A1). Am I correct that the appropriate code for generating these 6 maps in my design is:

-gltCode # ‘A : +1*A1’
-gltCode # 'A : +1*A2’

-gltCode # ‘B : +1

*B1’*

-gltCode # 'B : +1B2’

-gltCode # 'B : +1

-gltCode # ‘C : +1

*C1’*

-gltCode # 'C : +1C2’

-gltCode # 'C : +1

If this is not correct, can you let me know if there’s a way to generate these maps using -gltCode statements. I realize that I can always run 3dDeconvolve on only the trials for each level of a factor in the individual analyses, and then analyze these at the group level with 3dLME. If there’s any easier way using -gltCode, though, it would be preferable.

Q3. I would also like to obtain a brik for the grand mean. Am I correct that any of the following would work, and should be equivalent (again the design is fully crossed and balanced, with no missing data)?

-gltCode # ‘A : +1*A1 +1*A2’

-gltCode # ‘B : +1*B1 +1*B2’

-gltCode # ‘C : +1*C1 +1*C2’

If this is not correct, can you let me know if there’s another way to generate this map with a -gltCode statement. And again, if necessary, I assume that I could compute it by aggregating all trials at the individual level and then analyzing the individual maps at the group level.

Q4. When testing a simple effect of one factor at one level of a second factor, I’ve been using statements like:

-gltCode # ‘A : +1*A1 -1*A2’ : B +1*B1’
-gltCode # 'A : +1*A1 -1

*A2’ : B +1*B2’

I want to be sure that when specifying the level of B, regardless of whether it’s B1 or B2, the correct weight in BOTH cases is +1 (i.e., NOT +1 in one case and -1 in the other).

Q5. Imagine that I add a quantitative variable for an individual difference measures to the design, say Q. In a -gltCode statement, what would the following code (adapted from the 3dLME examples) request:

-gltCode # ‘A : +1*A1 Q :’

Is this asking for the interaction between A and Q at the level of A1? Or something else?

If I wanted the interaction between A and Q overall, how would I request it? I realize that there may be an F brik for this, but if I wanted a directional t brik, how would this be requsted in in gltCode statement?

Please feel free to add any further advice or suggestions that you see relevant.

Much thanks for your patience and assistance!

Larry