Test time adaptation is the process of adapting, in an unsupervised manner, a pre-trained source model to each incoming batch of the test data (i.e., without requiring a substantial portion of the test data to be available, as in traditional domain adaptation) and without access to the source data. Since it works with each batch of test data, it is well-suited for dynamic environments where decisions need to be made as the data is streaming in. Current test time adaptation methods are primarily focused on a single source model. We propose the first completely unsupervised Multi-source Test Time Adaptation (MeTA) framework that handles multiple source models and optimally combines them to adapt to the test data. MeTA has two distinguishing features. First, it efficiently obtains the optimal combination weights to combine the source models to adapt to the test data distribution. Second, it identifies which of the source model parameters to update so that only the model which is most correlated to the target data is adapted, leaving the less correlated ones untouched; this mitigates the issue of "forgetting" the source model parameters by focusing only on the source model that exhibits the strongest correlation with the test batch distribution. Experiments on diverse datasets demonstrate that the combination of multiple source models does at least as well as the best source (with hindsight knowledge), and performance does not degrade as the test data distribution changes over time (robust to forgetting).

测试时间自适应是将预训练的源模型无监督地适应到每个测试数据批次（无需大量测试数据，无法访问源数据）的过程，本研究提出了首个完全无监督的多源测试时间自适应框架（MeTA），它通过优化组合权重适应于测试数据分布，并只更新与目标数据最相关的源模型参数，避免“遗忘”源模型参数的问题。多个源模型的组合至少能与最佳源模型（具备先见之明）一样好，并且在测试数据分布随时间变化时性能不会下降（遗忘容忍性）。

MeTA: 多源测试时间适应