# Parametric Modulation- Group level

Hello,

I will be running a task where participants behave aggressively each trial to either mean or nice peers. So, each trial varies by peer reputation (mean or nice) and has an aggression level associated with it. I am interested in modeling that trial-by-trial aggression and so it seems I’ll need to do parametric modulation for the individual/first-level analyses. There are some message board posts on how to do this (thanks!!) so I understand how to set that up.

However, I’m unclear how to examine these relations across the whole group. For the group level analysis, how do I set up glt’s to examine brain and aggression relations for nice vs mean peers? And, conceptually, will this be a repeated measures ANCOVA then (aggression as between subjects variable and nice/mean peer reputation as within subjects factor)? Or, will this be multiple regression with aggression and peer reputation as DVs?

Thank you for the help!!

Is the following an accurate description of your experiment?

1. Are nice and mean two separate big categories in your experimental design?
2. Aggression is a behavioral measure at the trial level that is applicable to both mean and nice categories?

As for modulation analysis, the basic model at the subject level is the following formulation

y = a + b * x + e

where x is the modulation variable (aggression in your case). What is your effect of interest at the population level between the following two?

1. a: BOLD response after controlling the aggression, or
2. b: aggression effect

Hi Gang,

1. Are nice and mean two separate big categories in your experimental design?
Yes
2. Aggression is a behavioral measure at the trial level that is applicable to both mean and nice categories?
Yes

As for modulation analysis, the basic model at the subject level is the following formulation

y = a + b * x + e

where x is the modulation variable (aggression in your case). What is your effect of interest at the population level between the following two?

1. a: BOLD response after controlling the aggression, or
2. b: aggression effect

I would be interested in #2 the aggression effect.

Thank you!

If you only have one group of subjects, the population-level analysis would be just comparing the aggression effect between the two conditions of mean and nice? If so, that would be a paired t-test using 3dttest++. If you directly obtain the contrast of the aggression effect from each subject, that would be a one-sample t-test using 3dttest++ or 3dMEMA.

Thank you!