to mask or not

AFNI Message Board
1

Hi AFNI friends,

What is conventional wisdom regarding masking (or not)?

I have 4 modeled regressors. In a single trial, M occurs before 1, 2, or 3.

M is the result of a generic somatosensory/motor process. Responses to 1, 2, or 3 include the aforementioned generic somatosensory/motor process, but also include additional, distinct, sensory responses.

Think of reaching (M), versus reaching and acquiring (M+1, 2, or 3).

Can I mask the response to 1, 2, or 3 with mask M?

2

What do you mean by “mask the response” in this context? Do you mean modulate? Or mean to compute the amplitude of M and 1/2/3 separately, even if they are close in time?

3

Thanks Bob,

I have modeled each regressor (M, 1, 2, and 3), and created mask (M vs. baseline). Remember, in a given trial M occurs, with variable delay, before 1, 2, or 3.

Yes: compute the amplitude of M, and 1, 2, and 3 separately.

What do you think?

4

I still don’t understand what you mean by “mask” in this context. How is “M vs. baseline” a mask?

5

Sorry, let me be more specific:

I take the inverse (zeros become 1s; 1s become 0) of M v. baseline thresholded at p = 0.01, (or p = 0.005), and exclude those voxels in 3dLME or 3dANOVA by specifying this inverse mask with the line “-mask inverseM+orig.”