How to define an interaction model using dissimilarity matrices in CoSMoMVPA?

[Alessandro Benedetto]

Hello,
I am working on a project using CoSMoMVPA, and I need to create a model based on dissimilarity matrices for both main effects and their interaction. Currently, I am calculating the dissimilarity matrixes for the main effects as follow:

• Dissimilarity for condition A: A=∣xa​−ya​∣
• Dissimilarity for condition B: B=∣xb​−yb​∣

To compute the interaction term, I am using the product of the two vectors and then calculating the absolute difference:

• Interaction term: C=∣(xa​⋅xb​)−(ya​⋅yb​)∣

My questions are:

1. Is this method correct for capturing the interaction effect in CoSMoMVPA?
2. Is there a more appropriate way to compute interaction terms for dissimilarity matrices within this framework?

Thank you for your help!