Model-based Approaches for Scanning Keyboard Design: Present State and Future Directions

Model-based Approaches for Scanning Keyboard Design: Present State and Future Directions

Samit Bhattacharya
DOI: 10.4018/978-1-60566-206-0.ch017
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Many individuals with speech and motor disorders face problems in expressing themselves in an easy and intelligible way. An array of Augmentative and Alternative Communication (AAC) devices and techniques is used to alleviate their problems. One of the commonly used computer based AAC systems is the scanning keyboards. A scanning keyboard refers to an on-screen keyboard operated with a scanning input method. There are many ways to place alpha-numeric characters on the keyboard interface. Therefore, it is necessary to compare alternative layouts to determine the best one in terms of user performance. Usually, layouts are compared by testing prototypes with physically disabled users. This approach is problematic since it is difficult to get physically disabled users or collect data from those users. An alternative approach is to use models to compute user performance, which can serve as the basis of layout comparison as well as automatic design space exploration. Several of these models and design space exploration algorithms are reported in the literature. A review of these works is presented in this chapter. The chapter is concluded with a discussion on the limitations of the existing works and the issues that can be taken up for further research.
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Survey Of Aac Systems

There exists wide variation in the physical, cognitive and linguistic abilities of individuals who need AAC. In order to cater to diverse user requirements, different AAC systems and techniques have been developed. The simplest of these techniques include attention calling bell, communication through yes or no, gestures and message cards. The most sophisticated among these non-electronic means of augmentative communication are the communication boards. A communication board can contain alphanumeric characters, words, icons, symbols, phrases or sentences (Worah, 2001). In order to convey a message, users of such boards “point” (with fingers or head-mounted pointers) to the appropriate items present on the board. In addition to these non-electronic techniques, many computer-based AAC systems are also used. Computer-based systems can be classified depending on the nature of the input as the (a) non-text based and (b) text based.

In the non-text based AAC systems, communicative messages are composed with the selection of icons or images from the system interface. An example is the “MinSpeak” system (Albacete et al., 1998), where ambiguous icons (i.e. each icon having multiple meanings associated with it) are used as input. In order to form a communicative message, users select two or more of these icons in sequence, which is converted to a textual and/or spoken message. In the “Picture WordPower” by Nancy Inman (, messages are constructed with unambiguous icons. Each icon corresponds to a linguistic item. A user needs to select a sequence of these icons following the syntactic word ordering of English to form a message. Another system that uses unambiguous icons is the “iconCHAT” by Patel et al. (2004). In order to compose a message with “iconCHAT”, a user needs to first select the verb, and then specify the agent, object, and various other verb-dependent message components. A similar approach was reported by Bhattacharya and Basu (in press) to implement “Sanyog”, an iconic system in Indian languages. Apart from icons, symbols and sign languages are also used for non-text based AAC1.

Key Terms in this Chapter

Design Space: The set of all possible designs.

Text Entry Rate: Number of characters/words entered per second/minute (CPS/WPM). This metric is used to measure performance of character-level text entry systems.

Performance Models: Computational model of user performance.

Scanning Keyboards: Soft keyboards operated using an input method that involves scanning and access switches.

Design Space Exploration: The process of searching for a good design among all the designs in the design space.

Augmentative and Alternative Communication (AAC): Augmentative and alternative communication is any method that supplements or replaces speech and writing when these are temporarily or permanently impaired and inadequate to meet all or some of a person’s communication needs

Scanning: Scanning is the technique of periodic highlighting of on-screen elements.

Soft Keyboards: Soft keyboards are on-screen keyboards, i.e. the keys are laid out spatially on the computer screen.

Model-Based Design: Automated design techniques where performance models and design space exploration algorithms are used to design a system.

Access Switches: Specially designed input devices for motor-impaired computer users.

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