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Hong Kong Polytechnic University. Hong Kong ... Hong Kong Society for the Blind. Shum Shui Po .... This work is supported by the Hong Kong Jockey Club and.
Digital Library Access for Chinese Visually Impaired Robert Luk, Daniel Yeung, Qin Lu, Eric Leung and S.Y. Li

Fred Leung

Department of Computing Hong Kong Polytechnic University Hong Kong E-mail: {csrluk,csdaniel,csluqin}@comp.polyu.edu.hk ABSTRACT This paper describes our effort to make digital libraries (on the World Wide Web or in CD-ROMs) accessible to the Chinese visually impaired via a (Web) browser. The interface has an electromagnetic braille display for touch reading, as well as a bilingual English-Chinese text-tospeech system. The interface for navigating through the Web and the web pages is presented. Apart from web navigation, Chinese data entry is difficult even for the sighted users, due to the large Chinese character set. An advanced input method designed for the Chinese visually impaired is discussed. It enables the visually impaired to formulate both Boolean-type and natural language queries.

Division Head Adaptive Equipment Service Hong Kong Society for the Blind Shum Shui Po, HK E-mail: [email protected] The visually impaired who are native Chinese speakers are not as fortunate as the English speakers are. Development of software for the Chinese visually impaired focused mainly in building a specialized editor for the visually impaired to compose or read documents (e.g. Mao [1]). There has been no published work that makes digital libraries accessible to them. Apart from the difficulty of navigation through the WWW or the graphical user interface, Chinese braille does not correspond to Chinese text in a one-to-one manner, unlike English braille and English letters. A conversion procedure is necessary for formulating Chinese queries. We developed a Chinese speech-braille enabling system for he visually impaired to use Internet Explorers to access digital libraries. The interface assists the visually impaired to navigate web pages based on spatial clusters of information, table and sequential access. It also assists the visually impaired to convert braille code sequences to Chinese terms in order to formulate natural language or Boolean-type queries. Our interface can operate with other supporting software (like WinZip, Real audio player and Volume control) to enable downloading and playing audio data from audio digital libraries. In the rest of this paper, we focus our discussion in web navigation by spatial clustering and Chinese query formulation.

KEYWORDS: Digital library, accessibility, user interface design, browsing, assistive technology, the visually impaired INTRODUCTION The availability of digital libraries for the visually impaired is important in several respects. First, the labor and financial cost to assist the visually impaired, as well as the cost to produce special reading material is reduced. Second, the electronic reading material can be circulated to more audience simultaneously. Finally, the visually impaired who does not know braille can still enjoy reading using a speech synthesizer to read aloud the electronic text. To read or order reading material via WWW or CD-ROMs, the visually impaired can use a Web browser as the interface. However, Web browsers are designed as a graphical user interface for the sighted users. Fortunately, Microsoft has released Microsoft Active Accessibility (MSAA) to enable applications to access screen objects (e.g. menu item) in Microsoft Windows 95, 98 and NT. Commercial software for the visually impaired, like JAWS by Henter-Joyce, ScreenPower by Telesensory, Windows Bridge and Screen Reader by IBM have enabled the visually impaired to access the WWW.

NAVIGATING THE WEB (PAGE) The visually impaired navigates the web by entering the URL or via hyperlinks (in address book). Our current interface enables the user to jump to different hyperlinks by pressing the TAB key. Once the URL is found, the visually impaired needs to navigate through the web page to browse (by speech/touch-reading) as well as to enter queries and to select options during the browsing process. Navigating a web page poses several difficulties for the visually impaired. First, the spatial relation of the screen objects in a web page is not explicit in the presentation to the visually impaired. Second, there are too many details or irrelevant information in the web page that the visually impaired needs effort to browse (or by-pass). Finally, information that is presented visually in a sequence is broken down into small objects. Presentation of this information to the visually impaired has to connect the information into a non-interrupted sequence.

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Navigate by Spatial Clusters. In view of these difficulties, there are several methods to navigate a web page. One method is to organize the objects in the web page according to the spatial relations on the screen. Objects displayed near each other on the screen are grouped together. In this way, the user can jump between spatial clusters of information. The groups of information are found by a spatial clustering algorithm, similar to image layout analysis.

have the same braille code sequence and the time consuming process of selecting a candidate can be reduced. For flexibility, the user only needs to type the prefix of each braille code sequence for each character in the word. The word-based braille input also accepts new words, which are placed in a user-defined dictionary. In the sentence-based braille input, the user enters a string of braille codes that represent either a phrase or a sentence. Any substring of braille codes that corresponds to a Chinese character is delimited by a space character. When the user presses the automatic conversion key, the entire string is converted to a string of Chinese characters. If there are unrecognized braille code sequences, for instance an English word, no conversion will be carried out for them. Therefore, a Boolean-type query with terms expressed in braille code sequences can be converted as a sentence, and the Boolean operators (conjunction, disjunction and negation) and parentheses would remain unconverted. The conversion of braille codes to Chinese characters is based on a Markov language model. The most likely sequence of characters that correspond to the sequence of braille codes is found by the Viterbi algorithm [2], which seraches through a lattice (Figure 3).

Figure 1: Identification of information clusters (enclosed in blue rectangles) by a spatial clustering algorithm.

CHINESE QUERY FORMULATION Chinese search engines can accept queries based on Chinese spelling (called pinyin). However, there are a large number of Chinese (homonym) characters with the same spelling. This would affect the precision of the retrieval, which is undesirable for the visually impaired users, since they need to pay extra effort and time to browse through the search results. It would be more efficient if the visually impaired can pay more attention in formulating the query, which is usually short.

Figure 3: The lattice representing all possible character sequences of the Boolean query with terms expressed in braille code sequences.

ACKNOWLEDGMENTS This work is supported by the Hong Kong Jockey Club and PolyU Central Grant (Shopping List Project No. EMB4/3371/83). REFERENCES 1. Y.H. Mao and P. Han. Application of modern achievement in language processing to help visually th impaired people, Proc. of the 7 International Conference on Computer Processing of Oriental Languages, Vol. II, (April 1997), 223-227.

Figure 2: The Qwerty keyboard used to simulate the input by a phonotyper. Only six keys are needed (i.e. S, D, F, J, K and L) to represent a braille code.

Character-based braille input (Figure 2) is used by novice users who are not familiar with the braille code and it is used for single-character words. Word-based braille input achieves a much better typing speed. The long words rarely

2.

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A.J. Viterbi, Error bounds for convolutional codes and an optimal asymptotically decoding algorithm, IEEE Trans. on Information Theory, IT-13 (1967), 260-269.