Connectionist Temporal Fusion for Sign Language Translation

Continuous sign language translation (CSLT) is a weakly supervised problem aiming at translating vision-based videos into natural languages under complicated sign linguistics, where the ordered words in a sentence label have no exact boundary of each sign action in the video. This paper proposes a hybrid deep architecture which consists of a temporal convolution module (TCOV), a bidirectional gated recurrent unit module (BGRU), and a fusion layer module (FL) to address the CSLT problem. TCOV captures short-term temporal transition on adjacent clip features (local pattern), while BGRU keeps the long-term context transition across temporal dimension (global pattern). FL concatenates the feature embedding of TCOV and BGRU to learn their complementary relationship (mutual pattern). Thus we propose a joint connectionist temporal fusion (CTF) mechanism to utilize the merit of each module. The proposed joint CTC loss optimization and deep classification score-based decoding fusion strategy are designed to boost performance. With only once training, our model under the CTC constraints achieves comparable performance to other existing methods with multiple EM iterations. Experiments are tested and verified on a benchmark, i.e. the RWTH-PHOENIX-Weather dataset, which demonstrate the effectiveness of our proposed method.