Pre-trained Vision-Language Models Learn Discoverable Visual Concepts

TL;DR

Pre-trained vision-language models can learn and discover visual concepts like color and texture, which can be extracted using their interface with prompts, enabling better interpretability and reasoning.

Contribution

The paper introduces a new framework for identifying and ranking visual concepts learned by VLMs, addressing previous conflicting evaluation strategies.

Findings

VLMs learn diverse visual concepts that describe objects accurately.

The proposed CDL framework effectively discovers concepts based on mutual information.

Quantitative and human evaluations confirm the quality of discovered concepts.

Abstract

Do vision-language models (VLMs) pre-trained to caption an image of a "durian" learn visual concepts such as "brown" (color) and "spiky" (texture) at the same time? We aim to answer this question as visual concepts learned "for free" would enable wide applications such as neuro-symbolic reasoning or human-interpretable object classification. We assume that the visual concepts, if captured by pre-trained VLMs, can be extracted by their vision-language interface with text-based concept prompts. We observe that recent works prompting VLMs with concepts often differ in their strategies to define and evaluate the visual concepts, leading to conflicting conclusions. We propose a new concept definition strategy based on two observations: First, certain concept prompts include shortcuts that recognize correct concepts for wrong reasons; Second, multimodal information (e.g. visual discriminativeness, and textual knowledge) should be leveraged when selecting the concepts. Our proposed concept discovery and learning (CDL) framework is thus designed to identify a diverse list of generic visual concepts (e.g. "spiky" as opposed to "spiky durian"), which are ranked and selected based on visual and language mutual information. We carefully design quantitative and human evaluations of the discovered concepts on six diverse visual recognition datasets, which confirm that pre-trained VLMs do learn visual concepts that provide accurate and thorough descriptions for the recognized objects. All code and models are publicly released.