Attention-Guided Saliency Maps for Interpreting Visualization Literacy in VLMs

2026-07-17

AI Summary

This work addresses the limited interpretability of current vision-language models (VLMs) in understanding data visualizations, which hinders verification of whether their reasoning focuses on semantically relevant image regions. The authors propose a lightweight diagnostic saliency mapping method that, for the first time, aggregates attention weights across all layers and attention heads of a Transformer model with respect to visual tokens and back-projects them onto the image patch grid to establish direct correspondences between generated text and specific image regions. This approach requires no gradient computation and efficiently produces causally faithful explanations. Experimental results demonstrate that the resulting saliency maps accurately highlight the regions attended by the model, and deletion tests confirm their causal fidelity to the model’s behavior.

Abstract

Understanding how vision-language models (VLMs) interpret data visualizations remains an open problem, and is increasingly important as these models are used for analytical tasks where reliable reasoning is essential. We introduce a lightweight, diagnostic saliency map method tailored for text generation over images using transformer models, the current state-of-the-art models in visualization interpretation. Our approach aggregates the language model's attention over the visual tokens across all heads and layers, then maps this attention back onto the vision encoder's patch grid to localise it over the image, producing a direct correspondence between each generated answer token and the image regions it attended to. This yields fast, gradient-free saliency maps that expose how VLMs allocate focus across visual elements during answer generation, enabling inspection of whether model attention aligns with semantically relevant components. We evaluate our approach using a deletion metric which validates the causal faithfulness of our saliency maps to the model's behavior.

Problem

• vision-language models
• visualization literacy
• saliency maps
• model interpretability
• attention mechanism

Innovation

• saliency maps
• vision-language models
• attention aggregation
• visualization literacy
• gradient-free interpretation