The success of large language models (LLMs) in cognitive tasks prompts the question of whether their next-token prediction (NTP) paradigm can be adapted to model physiological signals from wearable devices. A key target for this adaptation is photoplethysmography (PPG), the most prevalent sensing modality in consumer wearables for non-invasive monitoring of diverse physiological conditions. Unlike in NLP, where NTP aligns with generative objectives, physiological signal analysis involves fundamentally different tasks, such as continuous parameter estimation (regression) and discrete state recognition (classification). This disparity creates a semantic mismatch between the pre-training paradigm and the downstream tasks. To bridge this gap, we propose PPGPT, the first foundation model that reformulates NTP into next-feature token prediction (NFTP), learning hierarchical feature transition probabilities to unify pre-training and downstream objectives. PPGPT features a novel dual-stream encoder that generates feature tokens by jointly modeling temporal dynamics and local-global morphological patterns. The model is developed using a two-stage training framework: it is first pre-trained on a large-scale mixed dataset of 1.6 billion data points and then validated on our newly released BioMTL benchmark, which includes data from 172 subjects over 285 days across seven different tasks. Extensive experiments show that PPGPT significantly outperforms competing methods, achieving a 16.5% improvement in F1-score and a 25.9% reduction in Mean Absolute Error (MAE). Furthermore, the model demonstrates robust few-shot learning capabilities.

Zero-Shot Sketch-Based Image Retrieval (ZS-SBIR) is an emerging research task that aims to retrieve data of new classes across sketches and images. It is challenging due to the heterogeneous distributions and the inconsistent semantics across seen and unseen classes of the cross-modal data of sketches and images. To realize knowledge transfer, the latest approaches introduce knowledge distillation, which optimizes the student network through the teacher signal distilled from the teacher network pre-trained on large-scale datasets. However, these methods often ignore the mispredictions of the teacher signal, which may make the model vulnerable when disturbed by the wrong output of the teacher network. To tackle the above issues, we propose a novel method termed Prototype-based Selective Knowledge Distillation (PSKD) for ZS-SBIR. Our PSKD method first learns a set of prototypes to represent categories and then utilizes an instance-level adaptive learning strategy to strengthen semantic relations between categories. Afterwards, a correlation matrix targeted for the downstream task is established through the prototypes. With the learned correlation matrix, the teacher signal given by transformers pre-trained on ImageNet and fine-tuned on the downstream dataset, can be reconstructed to weaken the impact of mispredictions and selectively distill knowledge on the student network. Extensive experiments conducted on three widely-used datasets demonstrate that the proposed PSKD method establishes the new state-of-the-art performance on all datasets for ZS-SBIR.