Understanding Video Transformers via Universal Concept Discovery
(2401.10831)Abstract
This paper studies the problem of concept-based interpretability of transformer representations for videos. Concretely, we seek to explain the decision-making process of video transformers based on high-level, spatiotemporal concepts that are automatically discovered. Prior research on concept-based interpretability has concentrated solely on image-level tasks. Comparatively, video models deal with the added temporal dimension, increasing complexity and posing challenges in identifying dynamic concepts over time. In this work, we systematically address these challenges by introducing the first Video Transformer Concept Discovery (VTCD) algorithm. To this end, we propose an efficient approach for unsupervised identification of units of video transformer representations - concepts, and ranking their importance to the output of a model. The resulting concepts are highly interpretable, revealing spatio-temporal reasoning mechanisms and object-centric representations in unstructured video models. Performing this analysis jointly over a diverse set of supervised and self-supervised representations, we discover that some of these mechanism are universal in video transformers. Finally, we show that VTCD can be used for fine-grained action recognition and video object segmentation.
Overview
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Researchers developed the Video Transformer Concept Discovery (VTCD) algorithm to interpret the inner workings of video transformers.
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VTCD parses layers of a transformer into discernible 'concepts', making them intuitive without requiring predefined labels.
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The algorithm aids transparency, regulatory compliance, risk minimization, and could inspire design improvements especially in video AI due to complex temporal dynamics.
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VTCD reveals that video transformers exhibit universal mechanisms, understanding object dynamics and sorting temporal information innately.
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Practically, VTCD enhances transformer performance; for example, it improved an action classification model's accuracy by 4.3% and reduced computation by one-third.
Interpretability in Video Transformers
Overview of Video Transformer Concept Discovery
Transformers have revolutionized the field of machine learning, particularly for tasks involving video. However, the complexity of these models often makes them veiled in mystery, leaving users unsure of how their internal processes lead to their conclusions. Addressing this gap, researchers have developed the Video Transformer Concept Discovery (VTCD) algorithm, positioning it as a pioneering approach for unveiling the inner workings of video transformers. VTCD is structured to parse layers of a transformer into discernible 'concepts' that are intuitive, even without a predefined label set.
The Importance of Understanding AI Decisions
Transparency within AI models is crucial, as it aligns with regulatory requirements, minimizes risks during deployment, and can inspire innovative design improvements. Particularly within video models, this interpretability is essential due to the added complexity introduced by the temporal dynamics of videos. Prior studies that have simplified the decision-making of AI have often overlooked the video domain. VTCD is designed to fill this gap by providing a look into a video transformer's reasoning by identifying significant spatio-temporal concepts and their contribution to the model's predictions.
Unveiling the Universal Mechanisms
Applying VTCD to diverse video transformer models trained for different objectives, researchers have discovered universal mechanisms. It appears that regardless of training objectives, video transformers share common spatio-temporal foundations early in their layers and exhibit object-central video representations in deeper layers. These insights largely suggest an innate capability of video transformers to sort through temporal information and understand object dynamics, even in the absence of supervised training.
Practical Applications and Performances
Beyond theoretical implications, VTCD has shown its practical worth. The algorithm can be used to refine pre-trained transformers by pruning less significant components, leading to enhanced model accuracy and efficiency. For instance, when applied to an action classification model, VTCD successfully improved accuracy by approximately 4.3% while cutting down computation by a third. This performance boost demonstrates VTCD's potential to contribute to more fine-tuned and cost-effective transformer applications in video analysis tasks.
In essence, VTCD stands as an important tool not only for demystifying the decision processes of video transformers but also for enhancing their performance for specialized tasks. As artificial intelligence continues to evolve and integrate into more domains, such tools will be increasingly valuable for making these powerful systems transparent and trustworthy.
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