  Recently, Chinese Spell Checking(CSC), a task to detect erroneous characters
in a sentence and correct them, has attracted extensive interest because of its
wide applications in various NLP tasks. Most of the existing methods have
utilized BERT to extract semantic information for CSC task. However, these
methods directly take sentences with only a few errors as inputs, where the
correct characters may leak answers to the model and dampen its ability to
capture distant context; while the erroneous characters may disturb the
semantic encoding process and result in poor representations. Based on such
observations, this paper proposes an n-gram masking layer that masks current
and/or surrounding tokens to avoid label leakage and error disturbance.
Moreover, considering that the mask strategy may ignore multi-modal information
indicated by errors, a novel dot-product gating mechanism is proposed to
integrate the phonological and morphological information with semantic
representation. Extensive experiments on SIGHAN datasets have demonstrated that
the pluggable n-gram masking mechanism can improve the performance of prevalent
CSC models and the proposed methods in this paper outperform multiple powerful
state-of-the-art models.
