How screen readers work

What is a screenreader?

Screen readers are software programs that allow blind or visually impaired users to read the text that is displayed on the computer screen with a speech synthesizer or braille display. A screen reader is the interface between the computer's operating system, its applications, and the user. 

Examples of common screen readers include:

  • JAWS: created and distributed through Freedom Scientific
  • NVDA: A free, open-source tool made available through the non-profit NVAccess
  • VoiceOver: integrated into MacOS and iOS

How does a screen reader work? 

The user sends commands by pressing different combinations of keys on the computer keyboard or braille display to instruct the speech synthesizer what to say and to speak automatically when changes occur on the computer screen. A command can instruct the synthesizer to read or spell a word, read a line or full screen of text, find a string of text on the screen, announce the location of the computer's cursor or focused item, and so on. In addition, it allows users to perform more advanced functions, such as locating text displayed in a certain color, reading pre-designated parts of the screen on demand, reading highlighted text, and identifying the active choice in a menu. Users may also use the spell checker in a word processor or read the cells of a spreadsheet with a screen reader.

Typically, a screen reader will start at the top of a website or document and read any text (including alternate text for images). Screen reader users often move through a website or document by using only the keyboard, as this provides precise navigation. Some screen readers allow the user to preview information, like the navigation bar or all the headings on a page, and skip the user to the desired section of the page. For this reason, using navigation styles like headings is part of creating accessible documents and web pages.

What does a screen reader sound like? 

To see a screen reader used on the web, watch this video from University of California - San Francisco. 

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