How Does A Screen Reader Work?
Screen readers can not see the screen in the same way that sighted individuals can, it does not view the screen and see words and icons and colors. It does not use a screen renderer to layout elements on a page. Instead it looks at the data and metadata of a page or view, including tags, semantic elements, and the content of text elements, and interprets these in order to present the user the page or application view.
This means that many of the design guidelines and paradigms which we take for granted in sighted design are not interpretable through a screen reader. Colors to indicate what elements are interactable, or to lead a user through a UI are not rendered in a screen reader. Text elements presented solely in images are not interpretable. Explanatory graphics and iconotic interfaces are opaque.
What is communicated instead is textual content which would be rendered by the browser or application used to access the content, and some of the semantic or descriptive metadata which has been added by the creator of the content or application. This results in a very different mode of access for users who are using a screen reader.
There are different interfaces which screen readers use, and different ways in which users can interact with them. Two of the main ways that users who employ the use of a screen reader to mediate their access use the tools are in navigating OS level applications, and browsing the web.
The Experience Of Using A Screen Reader:
To many sighted users, the use of a screen reader may feel limiting, and provide access to information at a rate which may seem cumbersome. Browsing the web using a tool which reads aloud each word on a page is a different experience than using the web as a sighted user. When a sighted user interacts with their usual interfaces, they often use mental shortcuts in order to quickly process information, and scan for relevant UI elements or information which they are looking for. Because screen readers can not interpret information which is communicated visually in the same way that a sighted user can, this can make navigation of UIs or content take more time or require a different cognitive load.
The speed at which an experienced screen reader user navigates and processes information with the tool requires practice and familiarity, like with any other interface. As users of these tools become more experienced and familiar with the tools and ideosycanicais of using them, they too begin to use mental shortcuts, and scan to find information. This results in a mode of access which can be difficult for non-expert users of these systems to process and understand.
Examples of Screen Readers:
Most modern, full featured OSs contain some tools for interpreting their interfaces for visually impared users. These tools provide a base-level set of tools for these users, and are often the first tools which these users use to navigate these environments. There are also 3rd party tools which solve problems or add additional features beyond what built in tools are designed to address.
OS level Screen Readers:
Screen readers are built into OSs in their accessibility features. These tools enable a user to navigate the OS and other applications without being able to see the screen. Many of these tools are designed in such a way that users can navigate the tools using both mouse/tough controls, where the element currently under focus is described, as well as keyboard based controls for navigating interfaces.
Web Based Screen Readers:
Browsers often have built-in tools for navigating the web through screen reading tools, but these tools are often not the focus of the teams which design these applications. This space is rich with 3rd party applications for screen reading which provide features beyond what web browser developers include by default in their applications. These can take the form of external application, screen reader only browsers, or add ons to existing browsers.
Application Specific Screen Readers/Interpreters:
Many applications have specific accessibility tools created for non-visual access to them. More discussion about these tools can be found in our section on other non-visual applied interfaces: Information on Other Non-Sighted Applications and Interfaces.
Design Guidelines:
There are many ways in which designers of interfaces can design interfaces to accommodate users of screen readers. More information and resources about these design practices and guidelines can be found in our section about designing non-sighted interfaces for the web: Design Guidelines for Non-Visual Accessible Web Design.