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Top1. Introduction
In recent years, considerable progress has been made in automatic speech recognition (ASR) technology, and applications such as speech assistants and speech input systems are becoming popular. However, in the state-of-art systems, recognition errors remain inevitable, due to environmental noise, accent, specific domain or topic, etc. In many cases, only a few errors can change the meaning of the sentence completely, which greatly affect the user's experience and the feasibility of the ASR technology.
To improve the feasibility of ASR systems, some researchers try to incorporate human-computer interaction technologies into ASR systems and allow the user to provide feedbacks (such as verification and correction) of the recognition results through human friendly interfaces. Many interaction methods for user feedback have been proposed, such as multi-modal interaction combining keyboard, re-speaking and handwriting (Oviatt, Cohen, et al., 2000) and candidate list (also known as alternative list) selection (Ogata and Goto, 2005; Nanjo, Akita and Kawahara, 2006; Cardinal, Boulianne, et al. 2007; Vertanen and Kristensson, 2011). In recent years, word candidate list has become the most popular interface for user feedback. In the interface, a candidate list is provided for each word in the recognition result, and when the 1-best result (namely, the top-1 candidate) is not correct, the error may be corrected by selecting candidate words in the candidate list. This correction method is user friendly and can greatly improve the efficiency of error correction.
For the generation of candidate lists, word confusion network (CN) [Xue and Zhao, 2005] extracted from the N-best lattice is widely used for languages such as English [Vertanen and Kristensson, 2011] and Japanese [Ogata and Goto, 2005]. For an utterance, a sequence of candidate lists can be obtained directly from the CN, with each candidate list providing alternative words (if any) besides the top-1 word. However, for the Chinese language, the word CN is not the best choice. In Chinese, words are formed by characters and most characters can be words by themselves while they are also included in multi-character words. Therefore, in candidate lists obtained from the word CN, a character may be repeatedly included in different candidate words in a candidate list or even in different candidate lists. This makes the candidate lists redundant and sometimes confusing to the user. To solve this problem, in our earlier work, candidate lists based on Chinese characters is introduced and a method for generation of the candidate lists is proposed [Li, Wang, et al., 2009]. In the candidate lists generated, each candidate is a Chinese character, and characters competing for each other is organized in one candidate list. This makes the interface present more information with limited candidates and be much friendlier to Chinese users.