Be Confident in What You Know: Bayesian Parameter Efficient Fine-Tuning of Vision Foundation Models

Large transformer-based foundation models have been commonly used as pre-trained models that can be adapted to different challenging datasets and settings with state-of-the-art generalization performance. Parameter efficient fine-tuning ( PEFT ) provides promising generalization performance in adaptation while incurring minimum computational overhead. However, adaptation of these foundation models through PEFT leads to accurate but severely underconfident models, especially in few-shot learning settings. Moreover, the adapted models lack accurate fine-grained uncertainty quantification capabilities limiting their broader applicability in critical domains. To fill out this critical gap, we develop a novel lightweight Bayesian Parameter Efficient Fine-Tuning (referred to as Bayesian-PEFT ) framework for large transformer-based foundation models. The framework integrates state-of-the-art PEFT techniques with two Bayesian components to address the under-confidence issue while ensuring reliable prediction under challenging few-shot settings. The first component performs base rate adjustment to strengthen the prior belief corresponding to the knowledge gained through pre-training, making the model more confident in its predictions; the second component builds an ev-idential ensemble that leverages belief regularization to ensure diversity among different ensemble components. Our thorough theoretical analysis justifies that the Bayesian components can ensure reliable and accurate few-shot adaptations with well-calibrated uncertainty quantification. Extensive experiments across diverse datasets, few-shot learning scenarios, and multiple PEFT techniques demonstrate the outstanding prediction and calibration performance by Bayesian-PEFT .