Continuous sign language recognition (CSLR) uses visual cues (e.g., hands, face, mouth, and body) to automatically recognize the sign language of deaf people, helping them to actively communicate with hearing people. The effects of these visual cues change dynamically with the demonstration of sign language. However, previous CSLR methods usually model visual information from the entire frame or simple fused visual cues, and thus do not well describe such dynamic change among visual cues. Therefore, we propose the Trustworthy Fusion Network ( TFN) of visual cues for CSLR, which comprises two fundamental modules: Intra-cue Cross-modality Feature Fusion module ( IntraCFF) and Inter-cue Trustworthy Fusion module (InterTF). IntraCFF uses the calibrated joint-belief method to dynamically fuse cross-modality features of RGB and keypoint information, to obtain a robust visual cue feature. InterTF innovatively employs the Dempster-Shafer Theory (DST) to evaluate the uncertainty of different cues in expressing sign movements. Then, the trustworthy fusion via DST is used to adaptively weigh and credibly fuse the visual cues based on uncertainty. In addition, to address the semantic gap when fusing different cues, we design consistency fusion constraints during the training stage. These constraints enhance the semantic consistency of different cues with global sign movements. Experiments on publicly CSLR datasets validate the effectiveness of our TFN.

Continuous sign language recognition (CSLR) is to recognize the glosses in a sign language video. Enhancing the generalization ability of CSLR's visual feature extractor is a worthy area of investigation. In this paper, we model glosses as priors that help to learn more generalizable visual features. Specifically, the signer-invariant gloss feature is extracted by a pre-trained gloss BERT model. Then we design a gloss prior guidance network (GPGN). It contains a novel parallel densely-connected temporal feature extraction (PDC-TFE) module for multi-resolution visual feature extraction. The PDC-TFE captures the complex temporal patterns of the glosses. The pre-trained gloss feature guides the visual feature learning through a cross-modality matching loss. We propose to formulate the cross-modality feature matching into a regularized optimal transport problem, it can be efficiently solved by a variant of the Sinkhorn algorithm. The GPGN parameters are learned by optimizing a weighted sum of the cross-modality matching loss and CTC loss. The experiment results on German and Chinese sign language benchmarks demonstrate that the proposed GPGN achieves competitive performance. The ablation study verifies the effectiveness of several critical components of the GPGN. Furthermore, the proposed pre-trained gloss BERT model and cross-modality matching can be seamlessly integrated into other RGB-cue-based CSLR methods as plug-and-play formulations to enhance the generalization ability of the visual feature extractor.

Continuous sign language recognition (CSLR) aims to recognize glosses in a sign language video. State-of-the-art methods typically have two modules, a spatial perception module and a temporal aggregation module, which are jointly learned end-to-end. Existing results in [9, 20, 25, 36] have indicated that, as the frontal component of the over-all model, the spatial perception module used for spatial feature extraction tends to be insufficiently trained. In this paper, we first conduct empirical studies and show that a shallow temporal aggregation module allows more thor-ough training of the spatial perception module. However, a shallow temporal aggregation module cannot well capture both local and global temporal context information in sign language. To address this dilemma, we propose a cross-temporal context aggregation (CTCA) model. Specifically, we build a dual-path network that contains two branches for perceptions of local temporal context and global temporal context. We further design a cross-context knowledge distil-lation learning objective to aggregate the two types of con-text and the linguistic prior. The knowledge distillation en-ables the resultant one-branch temporal aggregation mod-ule to perceive local-global temporal and semantic context. This shallow temporal perception module structure facili-tates spatial perception module learning. Extensive exper-iments on challenging CSLR benchmarks demonstrate that our method outperforms all state-of-the-art methods.

In this work, we target cross-domain action recognition (CDAR) in the video domain and propose a novel end-to-end pairwise two-stream ConvNets (PTC) algorithm for real-life conditions, in which only a few labeled samples are available. To cope with the limited training sample problem, we employ pairwise network architecture that can leverage training samples from a source domain and, thus, requires only a few labeled samples per category from the target domain. In particular, a frame self-attention mechanism and an adaptive weight scheme are embedded into the PTC network to adaptively combine the RGB and flow features. This design can effectively learn domain-invariant features for both the source and target domains. In addition, we propose a sphere boundary sample-selecting scheme that selects the training samples at the boundary of a class (in the feature space) to train the PTC model. In this way, a well-enhanced generalization capability can be achieved. To validate the effectiveness of our PTC model, we construct two CDAR data sets (SDAI Action I and SDAI Action II) that include indoor and outdoor environments; all actions and samples in these data sets were carefully collected from public action data sets. To the best of our knowledge, these are the first data sets specifically designed for the CDAR task. Extensive experiments were conducted on these two data sets. The results show that PTC outperforms state-of-the-art video action recognition methods in terms of both accuracy and training efficiency. It is noteworthy that when only two labeled training samples per category are used in the SDAI Action I data set, PTC achieves 21.9% and 6.8% improvement in accuracy over two-stream and temporal segment networks models, respectively. As an added contribution, the SDAI Action I and SDAI Action II data sets will be released to facilitate future research on the CDAR task.

Action recognition is a popular research topic in the computer vision and machine learning domains. Although many action recognition methods have been proposed, only a few researchers have focused on cross-domain few-shot action recognition, which must often be performed in real security surveillance. Since the problems of action recognition, domain adaptation, and few-shot learning need to be simultaneously solved, the cross-domain few-shot action recognition task is a challenging problem. To solve these issues, in this work, we develop a novel end-to-end pairwise attentive adversarial spatiotemporal network (PASTN) to perform the cross-domain few-shot action recognition task, in which spatiotemporal information acquisition, few-shot learning, and video domain adaptation are realised in a unified framework. Specifically, the Resnet-50 network is selected as the backbone of the PASTN, and a 3D convolution block is embedded in the top layer of the 2D CNN (ResNet-50) to capture the spatiotemporal representations. Moreover, a novel attentive adversarial network architecture is designed to align the spatiotemporal dynamics actions with higher domain discrepancies. In addition, the pairwise margin discrimination loss is designed for the pairwise network architecture to improve the discrimination of the learned domain-invariant spatiotemporal feature. The results of extensive experiments performed on three public benchmarks of the cross-domain action recognition datasets, including SDAI Action I, SDAI Action II and UCF50-OlympicSport, demonstrate that the proposed PASTN can significantly outperform the state-of-the-art cross-domain action recognition methods in terms of both the accuracy and computational time. Even when only two labelled training samples per category are considered in the office1 scenario of the SDAI Action I dataset, the accuracy of the PASTN is improved by 6.1%, 10.9%, 16.8%, and 14% compared to that of the $TA^{3}N$ , TemporalPooling, I3D, and P3D methods, respectively.