NPEFF: Non-Negative Per-Example Fisher Factorization
Michael Matena Colin Raffel
As deep learning models are deployed in more and more settings, it becomes
increasingly important to be able to understand why they produce a given
prediction, but interpretation of these models remains a challenge. In this
paper, we introduce a novel interpretability method called NPEFF that is
readily applicable to any end-to-end differentiable model. It operates on the
principle that processing of a characteristic shared across different examples
involves a specific subset of model parameters. We perform NPEFF by decomposing
each example's Fisher information matrix as a non-negative sum of components.
These components take the form of either non-negative vectors or rank-1
positive semi-definite matrices depending on whether we are using diagonal or
low-rank Fisher representations, respectively. For the latter form, we
introduce a novel and highly scalable algorithm. We demonstrate that components
recovered by NPEFF have interpretable tunings through experiments on language
and vision models. Using unique properties of NPEFF's parameter-space
representations, we ran extensive experiments to verify that the connections
between directions in parameters space and examples recovered by NPEFF actually
reflect the model's processing. We further demonstrate NPEFF's ability to
uncover the actual processing strategies used by a TRACR-compiled model. We
further explore a potential application of NPEFF in uncovering and correcting
flawed heuristics used by a model. We release our code to facilitate research
using NPEFF.