Design and Implementation of a Chorded On-Screen Keyboard for People with Physical Impairments

A new assistive technology solution for physically impaired computer users was presented at the 10th International Conference on Computers Helping People with Special Needs (ICCHP), held on July 12th -14th 2006, at the University of Linz, Austria.

The paper proposes the feasibility of an alternative on-screen keyboard for people with physical impairments and looks at evaluating the effectiveness of the chorded input method. Its design is based on the human computer interface and gives a visual guide and instantaneous feedback. It also helps with the navigation of characters. The system’s core usability analysis criterion includes the learning ability, efficiency of using and subjective satisfaction.

Using a standard keyboard might seem quite normal to most people, but it can be a strenuous task for people with physical impairments like postural limitations, muscle weakness or limited movements. Their impairment might restrict accessibility to a lot of features and also result in high error rates, fatigue and inefficiency. The typical on-screen keyboard is an image of a standard keyboard, following the same QWERTY layout. The efficiency of a text entry depends on the sustainability of control interface, including proper selection methods and keyboard layouts, which doesn’t work well enough for people with physical impairments on standard keyboards.

Chorded keyboards use a combination of certain keys to create keystrokes for every letter. It might take time getting used to the chorded keyboard, but with practice, associating the finger combinations with their corresponding actions becomes easy. Chorded keyboards facilitate a faster word transcription processing than the QWERTY keyboard, possibly due to reduced movement-time requirements. The numeric-based input method has been applied here, where the user presses two numeric keys to generate character.

The chorded keyboard works on the principle of universal design, displaying a window that the user can move, resize the layout and receive feedback. It is equipped with nine layouts, can work with multiple access devices, and supports five alternative input methods. The users also have the option to create their individual virtual keyboards by simply rearranging the special layout. The system can also work in sync with various physical devices like N-fingers, USB calculator, PDAs, and other devices.

Based on the square layout, a group-row-column scanning has been created, which is predicted to be more efficient than row-column scanning with one switch activation. It allows people with disabilities to move the mouse pointer without any pointing device. Also, this method requires less cognitive effort than the chorded input method. To evaluate the usability, a trial run involving text entry tasks was performed on an able-bodied person. The subject’s performance on the chorded keyboard went from 23.9 correct characters per minute in the first trial to 64.7 characters per minute in the last trial, reinforcing the potential and effectiveness of the chorded keyboard.

Many assistive technology solutions are commercially available today; however, not much has been done in the input devices segment for the physically impaired. The alternative on-screen keyboard presented in this paper focuses on creating accessible computing facilities for the physically impaired, broadening their horizons. It is expected to help people with motor impairment, and also those with cerebral palsy or muscular dystrophy.