Representational dissimilarity matrix ($D_{ij}=1-\mathrm{corr}(z_i,z_j)$)

A matrix whose entry $D_{ij}$ describes how differently a system responds to stimuli $i$ and $j$. One convention is $D_{ij}=1-\mathrm{corr}(z_i,z_j)$ when the response vectors have nonzero variance. Such a dissimilarity need not satisfy every metric axiom. Model comparison must control fitted transformations and use held-out data.