Federated zero-shot learning with mid-level semantic knowledge transfer

Conventional centralized deep learning paradigms are not feasible when data from different sources cannot be shared due to data privacy or transmission limitation. To resolve this problem, federated learning has been introduced to transfer knowledge across multiple sources (clients) with non-shared data while optimizing a globally generalized central model (server). Existing federated learning paradigms mostly focus on transmitting image encoders that take instance-sensitive images as input, making them less generalizable and vulnerable to privacy inference attacks. In contrast, in this work, we consider transferring mid-level semantic knowledge (such as attribute) which is not sensitive to specific objects of interest and therefore is more privacy-preserving and general. To this end, we formulate a new Federated Zero-Shot Learning (FZSL) paradigm to learn mid-level semantic knowledge at multiple local clients with non-shared local data and cumulatively aggregate a globally generalized central model for deployment. To improve model discriminative ability, we explore semantic knowledge available from either a language or a vision-language foundation model in order to enrich the mid-level semantic space in FZSL. Extensive experiments on five zero-shot learning benchmark datasets validate the effectiveness of our approach for optimizing a generalizable federated learning model with mid-level semantic knowledge transfer.