Thomas Fel

Hi đź‘‹

I am Thomas Fel, a 2nd year French PhD student (2021 - 2024) student supervised by Thomas Serre At ANITI (Toulouse, France) & Brown University (Boston, USA). I am also part of the incredible DEEL core team.

I'm interested in Explainability (XAI), computer vision, optimization and certification of neural network systems. Most of my research involves reverse engineering existing neural networks to understand their critical strategies. In my free time I also like to contribute to open source project in particular, I am the author of Xplique .  /  Google Scholar  /  Twitter  /  Github

  • 09/2022 : 3 papers accepted at NeurIPS!
  • 07/2022 : Oral presentation of 'Don't lie to me' at ICML Workshop
  • 06/2022 : Presentation of Xplique at CVPR
  • 12/2021 : 'How Good is your Explanation?' accepted at WACV 2022!
  • 09/2021 : Sobol Attribution Method accepted at NeurIPS!
  • 04/2021 : Official start of the thesis

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CRAFT: Concept Recursive Activation FacTorization
Thomas Fel*, Agustin Picard*, Louis Béthune*, Thibaut Boissin*, David Vigouroux, Julien Colin, Rémi Cadène, Thomas Serre
Under review, 2022

Despite their considerable potential, concept-based explainability methods have received relatively little attention, and explaining what’s driving models’ decisions and where it’s located in the input is still an open problem. To tackle this, we revisit unsupervised concept extraction techniques for explaining the decisions of deep neural networks and present CRAFT – a framework to generate concept-based explanations for understanding individual predictions and the model’s high-level logic for whole classes. CRAFT takes advantage of a novel method for recursively decomposing higher-level concepts into more elementary ones, combined with a novel approach for better estimating the importance of identified concepts with Sobol indices. Furthermore, we show how implicit differentiation can be used to generate concept-wise attribution explanations for individual images. We further demonstrate through fidelity metrics that our proposed concept importance estimation technique is more faithful to the model than previous methods, and, through human psychophysic experiments, we confirm that our recursive decomposition can generate meaningful and accurate concepts. Finally, we illustrate CRAFT’s potential to enable the understanding of predictions of trained models on multiple use-cases by producing meaningful concept-based explanations.

Harmonizing the object recognition strategies of deep neural networks with humans
Thomas Fel*, Ivan Felipe*, Drew Linsley*, Thomas Serre
NeurIPS Proceedings of the Conference on Neural Information Processing Systems, 2022

The many successes of deep neural networks (DNNs) over the past decade have largely been driven by computational scale rather than insights from biological intelligence. Here, we explore if these trends have also carried concomitant improvements in explaining the visual strategies humans rely on for object recognition. We do this by comparing two related but distinct properties of visual strategies in humans and DNNs: where they believe important visual features are in images and how they use those features to categorize objects. Across 84 different DNNs trained on ImageNet and three independent datasets measuring the where and the how of human visual strategies for object recognition on those images, we find a systematic trade-off between DNN categorization accuracy and alignment with human visual strategies for object recognition. State-of-the-art DNNs are progressively becoming less aligned with humans as their accuracy improves. We rectify this growing issue with our harmonization loss: a general-purpose training routine that both aligns DNN and human visual strategies and improves categorization accuracy. Our work represents the first demonstration that the scaling laws that are guiding the design of DNNs today have also produced worse models of human vision.

What I Cannot Predict, I Do Not Understand: A Human-Centered Evaluation Framework for Explainability Methods
Julien Colin*, Thomas Fel*, Rémi Cadène, Thomas Serre.
NeurIPS Proceedings of the Conference on Neural Information Processing Systems, 2022

In this work, we conducted psychophysics experiments at scale to evaluate the ability of human participants to leverage representative attribution methods for understanding the behavior of different image classifiers representing three real-world scenarios: (1) identifying bias, (2) characterizing novel strategy and (3) understanding failure cases. Our results demonstrate that the degree to which individual attribution methods help human participants better understand an AI system varied widely across these scenarios. This suggests a critical need for the field to move past quantitative improvements of current attribution methods.

Making Sense of Dependence: Efficient Black-box Explanations Using Dependence Measure
Paul Novello, Thomas Fel, David Vigouroux
NeurIPS Proceedings of the Conference on Neural Information Processing Systems, 2022

This paper could be seen as a follow-up to Look at the variance and further improves the efficiency of black-box methods using Hilbert-Schmidt Independence Criterion (HSIC). HSIC measures the dependence between regions of an input image and the output of a model based on kernel embeddings of distributions. Our experiments show that HSIC is up to 8 times faster than the previous best black-box attribution methods while being as faithful. Importantly, we show that these advances can be transposed to efficiently and faithfully explain object detection models such as YOLOv4.

Don't Lie to Me! Robust and Efficient Explainability with Verified Perturbation Analysis
Thomas Fel*, Melanie Ducoffe*, David Vigouroux, Remi Cadene, Mikael Capelle, Claire Nicodeme, Thomas Serre
ICML Workshop on Formal Verification of Machine Learning (Oral), 2022

In this work, we propose the first explainability method based on formal method and therefore able to meet certification requirements. Specifically, we introduce EVA (Explaining using Verified perturbation Analysis) -- the first explainability method guarantee to have an exhaustive exploration of a perturbation space. We leverage the beneficial properties of verified perturbation analysis -- time efficiency, tractability and guaranteed complete coverage of a manifold -- to efficiently characterize the input variables that are most likely to drive the model decision. We evaluate the approach systematically and demonstrate state-of-the-art results on multiple benchmarks.

When adversarial attacks become interpretable counterfactual explanations
Mathieu Serrurier, Franck Mamalet, Thomas Fel, Louis BĂ©thune, Thibaut Boissin
Under review, 2022

We argue that, when learning a 1-Lipschitz neural network with the dual loss of an optimal transportation problem, the gradient of the model is both the direction of the transportation plan and the direction to the closest adversarial attack. Traveling along the gradient to the decision boundary is no more an adversarial attack but becomes a counterfactual explanation, explicitly transporting from one class to the other. Through extensive experiments on XAI metrics, we find that the simple saliency map method, applied on such networks, becomes a reliable explanation! The proposed networks were already known to be certifiably robust, and we prove that they are also tailored for explainability.

Xplique: A Deep Learning Explainability Toolbox
Thomas Fel*, Lucas Hervier*, David Vigouroux, Antonin Poche, Justin Plakoo, Remi Cadene, Mathieu Chalvidal, Julien Colin, Thibaut Boissin, Louis Bethune, Agustin Picard, Claire Nicodeme, Laurent Gardes, Gregory Flandin, Thomas Serre
CVPR Workshop on Explainable Artificial Intelligence for Computer Vision, 2022

For more than a year, I worked alongside my thesis to implement more than fifty explainability papers. Xplique is the result of this work, it is a library that I develop and maintain. The library is composed of several modules: (1) the Attributions Methods module, (2) The Feature Visualization module, (3) The Concepts module and (4) the Metrics module.

Look at the Variance! Efficient Black-box Explanations with Sobol-based Sensitivity Analysis
Thomas Fel*, Rémi Cadène*, Mathieu Chalvidal, Matthieu Cord, David Vigouroux, Thomas Serre.
NeurIPSProceedings of the Conference on Neural Information Processing Systems, 2021

We describe a novel and efficient black-box attribution method which is grounded in Sensitivity Analysis and uses Sobol indices. Beyond modeling the individual contributions of image regions, Sobol indices provide an efficient way to capture higher-order interactions between image regions and their contributions to a neural network's prediction through the lens of variance.

How Good is your Explanation? Algorithmic Stability Measures to Assess the Quality of Explanations for Deep Neural Networks
Thomas Fel, David Vigouroux, Rémi Cadène, Thomas Serre.
WACVProceedings of the IEEE/CVF Winter Conference on Applications of Computer Vision, 2022

We propose two new measures to evaluate explanations borrowed from the field of algorithmic stability: mean generalizability MeGe and relative consistency ReCo. We conduct extensive experiments on different network architectures, common explainability methods, and several image datasets to demonstrate the benefits of the proposed metrics and show that popular fidelity measures are not sufficient to guarantee trustworthy explanations. Finally, we found that 1-Lipschitz networks produce explanations with higher MeGe and ReCo than common neural networks.