In this paper we present a novel approach to continuous, whole-sentence ASL recognition that uses phonemes instead of whole signs as the basic units. Our approach is based on a sequential phonological model of ASL. According to this model the ASL signs can be broken into movements and holds, which are both considered phonemes. This model does away with the distinction between whole signs and epenthesis movements that we made in previous work. Instead, epenthesis movements are just like the other movements that constitute the signs. We subsequently train Hidden Markov Models (HMMs) to recognize the phonemes, instead of whole signs and epenthesis movements that we recognized previously. Because the number of phonemes is limited, HMM-based training and recognition of the ASL signal becomes computationally more tractable and has the potential to lead to the recognition of large-scale vocabularies. We experimented with a 22 word vocabulary, and we achieved similar recognition rates with phoneme-and word-based approaches. This result is very promising for scaling the task in the future.
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