Hi Gang!

Sorry for a late reply, I have been away.

Quote
Gang
Let me try to understand the situation. You have two conditions, A and B, each of which has 3 trials. Each trial lasts for 10 seconds. In addition, you have behavioral data (pleasantness) that are associated with each trial. Is this accurate?

First of all, the number of trials per condition seems too few to achieve a robust estimate for the pleasantness effect.

Well, almost. This was just a simplified example for me to understand. The actual scenario is this:

4 Conditions:
A = Fast Touch on Arm
B = Fast touch in Palm
C = Slow Touch on Arm
D = Fast touch in Palm

Each condition consists of more than 5 onsets (don't remember exactly).

The researchers are doing a un-modulated analysis (just onset:duration) of this but since the subjects also rate the pleasentness of each onset they also want to investigate which areas of the brain that correlate with the rating: e.g.: Are some areas activated more when the subject is finding something more pleasent?

1) Is comparing the betas of e.g. A and C for in a normal un-modulated design the same thing as comparing b0 from A and C using the modulated stim files? Or do they differ since the pleasentness is not controlled for in the normal/un-modulated scenario? Like you wrote:

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Gang
Specifically, the first regressor corresponds to the condition effect (let's call it b0) when the behavioral data is controlled at the mean while the second one is associated with the pleasantness effect (let's call it b1) for that condition.

2) What would be the interpreation of comparing b0 across A and C when centering across A and C instead of centering within the conditions? If the centering matters the variance sucked up by b1 from A and C would differ (assuming I understood 1 correct).

3) In the modulated case: What is the interpretation of comparing b1 across e.g. condition A and C when it comes to centering? Since they by default are de-menaed within each condition one would have a hard time finding any thing (if the rating differs equally but from different means), right? Does the interpretation change when centering across conditions?

So to summerize they want to find areas that correlate with the rating (i.e. what areas activate more, or less, when rating something high, or low) and then see if any of these areas (or other) also differ between e.g. location of touch.

Does this make sense?

Thanks!



Edited 2 time(s). Last edit at 10/23/2017 02:47PM by Robin.