BendVLM: Test-Time Debiasing of Vision-Language Embeddings

Vision-language model (VLM) embeddings have been shown to encode biases present in their training data, such as societal biases that prescribe negative characteristics to members of various racial and gender identities. VLMs are being quickly adopted for a variety of tasks ranging from few-shot classification to text-guided image generation, making debiasing VLM embeddings crucial. Debiasing approaches that fine-tune the VLM often suffer from catastrophic forgetting. On the other hand, fine-tuning-free methods typically utilize a"one-size-fits-all"approach that assumes that correlation with the spurious attribute can be explained using a single linear direction across all possible inputs. In this work, we propose Bend-VLM, a nonlinear, fine-tuning-free approach for VLM embedding debiasing that tailors the debiasing operation to each unique input. This allows for a more flexible debiasing approach. Additionally, we do not require knowledge of the set of inputs a priori to inference time, making our method more appropriate for online, open-set tasks such as retrieval and text guided image generation.

Paper

Similar papers

Peer review

Reviewer xaVq8/10 · confidence 3/52024-06-28

Summary

This paper presents to address the bias problem in CLIP models from a novel angle - directly debiasing CLIP without fine-tuning. To begin with, this work defines two metrics: CCF and CCFD, which can quantify the bias effect of CLIP embeddings. The authors then propose a method involving two approaches to address the bias problem. The experiments are conducted on three human face-aware datasets. As can be observed from the experimental results, the proposed can outperform two baselines.

Strengths

- This paper studies a novel perspective of CLIP embedding debiasing - zero-shot debiasing without fine-tuning CLIP on downstream datasets. - The two defined bias-aware metrics seem interesting and practical. - The authors provide detailed proof for their second method component. - The proposed method achieves better performance than other baselines.

Weaknesses

- I'm a little confused about the original model's performance in image classification and image-text retrieval. Generally, after debiasing, the original downstream model performance will face certain degradation. However, this paper does not show this. Is it because this zero-shot way does not change the original CLIP embeddings? - The authors should at least provide some time efficiency evidence to show the effectiveness of the proposed method, since their method utilizes another LLM (though not very large). - I'm also not sure about the usefulness of the second approach - using reference images to equalize text embeddings. To me, the first orthogonal way is already good enough as per previous studies. Besides, there are no ablation studies on these two. - Why did the authors compute the CCF and CCDF for both their method and baselines? - Figure 1 is not a good example. It is because the improvement is largely limited - from 0.03 to 0.01.

Questions

Please refer to the weakness part. Overall I like this paper and I do believe this paper offers some significant insights.

Rating

8

Confidence

3

Soundness

3

Presentation

3

Contribution

4

Limitations

NA

Reviewer tPdX5/10 · confidence 4/52024-07-11

Summary

This paper focuses on debiasing VLM embeddings and proposes a fine-tuning-free method for online open-set embedding debiasing and tailors the debiasing operation to each unique input, which is advanced over the previous one-size-fits-all linear approach. The paper assumes that the debiased embeddings should satisfy the criteria of Class Conditionally Fair. In addition to mapping embeddings to the direction orthogonal to the protected attribute, it utilizes the reference image dataset to make relevant images from each attribute group equally similar to the query embedding, while ensuring debiased embedding does not lose information beyond protected attributes.

Strengths

+ Superior to the fine-tuning method that reduces the model accuracy and generalizability and fine-tuning-free method that uses one-size-fits-all linear debiasing functions for every input, the paper proposes to tailor the debiasing operation to each unique input online. + The paper formalizes the Class Conditionally Fair conditions that ideal debiased embedding should meet and designs a corresponding two-phase debiasing pipeline.

Weaknesses

1. The “open-set” ability of BEND-VLM may be overstated. The process of debiasing in BEND-VLM cannot avoid the defined attributes. It is impossible to know the attributes (didn't happen in training) of a completely new class, leading to the collapse of BEND-VLM's debiasing ability. 2. The paper seems to neglect to explain why can the proposed BEND-VLM overcomes catastrophic forgetting (the aspect in which the proposed BEND-VLM is stronger than fine-tuning-based methods), which is one of the main challenges that BEND-VLM overcomes. 3. All definitions and lemmas should be organized more formally.

Questions

See Weaknesses.

Rating

5

Confidence

4

Soundness

3

Presentation

2

Contribution

2

Limitations

See Weaknesses.

Reviewer kcNf6/10 · confidence 3/52024-07-12

Summary

The paper introduces a novel approach named BEND-VLM (Bias Elimination with Nonlinear Debiasing of Vision Language Models), designed to debias vision-language model embeddings at test time. The key innovation lies in a fine-tuning-free, nonlinear debiasing method that is adaptive to each specific query, enhancing flexibility and robustness in online, open-set tasks like image retrieval and text-guided image generation.

Strengths

S1: The BEND-VLM method addresses critical limitations of existing debiasing techniques by employing a nonlinear, fine-tuning-free approach. The adaptability to unique inputs during test time represents a significant advancement over traditional "one-size-fits-all" methods. S2: The two-step debiasing process, involving orthogonal projection and constrained optimization using a reference dataset, is well-conceived and effectively mitigates bias without degrading the model's performance.

Weaknesses

W1: BEND-VLM's reliance on a reference dataset with protected attribute annotations may limit its applicability in scenarios where such datasets are unavailable or impractical to obtain. The authors acknowledge this limitation but it would be better if there is an ablation for the reference dataset and desired properties of the reference dataset. W2: The approach focuses on debiasing based on specific attributes (e.g., gender, race), but it does not explicitly address contextual biases that might arise from the interplay of multiple attributes or the broader context of the query. Complex scenarios where biases are context-dependent require more sophisticated handling. It would be better if the paper discussed how to use the method for this kind of situation.

Questions

Please refer to "weakness".

Rating

6

Confidence

3

Soundness

3

Presentation

3

Contribution

3

Limitations

Please refer to "weakness".

Reviewer GYMR6/10 · confidence 3/52024-07-14

Summary

This paper proposes a two step test-time debasing method for VLMs. In the first step, an orthogonalizing approach is applied to text embeddings. In the second step, a constraint is utilized to equalize the distances between the debiased embeddings and images from a reference dataset. Experimental results show its effectiveness in mitigating stereotype biases.

Strengths

- This paper prosposes a novel strategy which uses a reference image dataset to make the query embeddings equidistant to the relevant images of different gender/ race. - Experimental results show its effectiveness with regard to mitigating stereotype biases.

Weaknesses

- Missing ablation study. The experimental section does not show how each step contributes to the debasing performance. For example, only use step 2. - The proposed method uses a two-step debiasing strategy. Besides, a LLM is also used to help with the attribute augment. How is the efficiency of the proposed method? Can the authors provide a detailed time comparison? - This paper claimed debiasing of VLMs but in experiments only CLIP models are used. Can the proposed method debias other VLMs?

Questions

See weaknesses above.

Rating

6

Confidence

3

Soundness

2

Presentation

3

Contribution

2

Limitations

Please see the questions and experiments I suggested above. I will be carefully reviewing the rebuttal as well as the opinions of the other reviewers to decide if I would like to change my rating.

Reviewer tPdX2024-08-07

The author's response addressed my concerns well.

Reviewer GYMR2024-08-12

The author's response addressed my concerns. I changed my rating to 6.

Authorsrebuttal2024-08-13

Thank you for your time and expertise providing an ethics review to our work. We are glad to see that you agree that there are no ethical issues with our work. We are happy to extend the discussion of our approach to multiple attributes in our camera-ready version. We have added a new experiment on intersectional bias in our general rebuttal, and will be adding this to our main paper. For attributes like marital status, the datasets we've investigated do not contain labels for this so we are unable to evaluate bias for marital status in this case. We will make it clear in our limitations that we perform debiasing for attributes for which we have some labeled examples.

Reviewer xaVq2024-08-14

Response to rebuttal

I previously held a positive view of this paper. After reading the authors' rebuttal, I chose to maintain my original acceptance score.

Authorsrebuttal2024-08-14

Thank you

Thank you for the constructive feedback and support for our work. We're very happy that you continue to recommend acceptance.

Program Chairsdecision2024-09-25

Decision

Accept (poster)

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