A screen reader is a software application that enables people with severe visual impairments to use a computer. Screen readers work closely with the computer’s Operating System (OS) to provide information about icons, menus, dialogue boxes, files and folders. A screen reader provides access to the entire OS that it works with, including many common applications.
A screen reader uses a Text-To-Speech (TTS) engine to translate on-screen information into speech, which can be heard through earphones or speakers. A TTS may be a software application that comes bundled with the screen reader, or it may be a hardware device that plugs into the computer. Originally, before computers had soundcards, screen readers always used hardware TTS devices, but now that soundcards come as standard on all computers many find that a software TTS is preferable. In addition to speech feedback, screen readers are also capable of providing information in Braille. An external hardware device, known as a refreshable Braille display is needed for this. A refreshable Braille display contains one or more rows of cells. Each cell can be formed into the shape of a Braille character, a series of dots that are similar to domino dots in their layout. As the information on the computer screen changes, so does the Braille characters on the display change, providing refreshable information directly from the computer. Whilst it is possible to use either format independently, Braille output is commonly used in conjunction with speech output.