For people with severe vision impairments or blindness, a screen reader is a device or piece of software that allows them to interact with a computer. Users of screen readers are unable to see clearly, so the screen reader reads out, so that they can use the website. Screen readers vary in their hardware and software models, with some displaying website content as braille and others communicating content verbally. It is generally necessary for screen readers to be active from the moment the user turns on their computer, since they cannot operate the computer with a mouse. In addition to those with severe vision disabilities and those with no vision, screen readers are also helpful for illiterate people and those with certain learning and cognitive disabilities. Someone with severe dyslexia would be an example of this.