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Considering Specific Disabilities

Following the guidelines in “Basic Design Requirements” will help you design an easy-to-use application that will be easy to access-enable. There may be specific information about particular disabilities you don’t know, however, and this information is useful to keep in mind during the design process.

The following sections describe some broad categories of disabilities and offer suggestions for specific design solutions and adaptations you can make. The main theme of these suggestions is to provide as many alternate modes of content display as possible. The more ways your application presents information, the more likely your users will be to find the way that suits them best.

In this section:

Visual Disabilities
Hearing Disabilities
Motor and Cognitive Disabilities

Visual Disabilities

Visual disabilities include blindness, color blindness, and low vision. In addition to making your application accessible to assistive applications, such as screen readers, you should also consider the following:

• Although color can greatly enhance a user interface, make sure it is not the only source of information. A color blind user may not be able to distinguish between two objects that differ only in color.

• Provide an audio option to all visual cues and feedback. Your application should make it easy to replace visual communication with audio communication.

• Provide an option to present images and animated content in an alternate manner. If your application displays an image or animation, consider providing your own succinct descriptions of these elements so blind or low-vision users can benefit from the information they convey.

Hearing Disabilities

People with hearing disabilities may have difficulty distinguishing your application’s sound effects from ambient noise or may not be able to hear them at all. Users without hearing disabilities may find themselves in circumstances in which audio output from an application is inappropriate (in a library, for example). Be sure to consider these points as you design the audio output of your application.

Your application should not override the audio-output settings the user selects in System Preferences. In addition, you should provide a visual option to all audio cues and feedback. Your application should make it easy to replace audio communication with visual communication. For example, a “beep” can be replaced or accompanied by a flash of the display screen.

Motor and Cognitive Disabilities

People with motor disabilities may need to use alternatives to the standard mouse and keyboard input devices. Other users may have difficulty with the fine motor control required to double-click a mouse or to press key combinations on the keyboard. Users with cognitive or learning disabilities may need extra time to complete tasks or respond to alerts.

For the most part, support for motor disabilities is provided at the hardware or operating system level. Mac OS X provides many such solutions in the Universal Access preferences. The Sticky Keys feature, for example, allows a user to type the keys in a key combination sequentially, instead of simultaneously. As an application developer, therefore, the most important thing you can do is to access-enable you application so your users can deploy the assistive technologies of their choice.

A feature such as Sticky Keys can also be helpful to a user with a cognitive or learning disability that makes it difficult to perform simultaneous tasks. An application that provides its output in both visual and auditory modes (especially simultaneously) can enhance comprehension. Users with such disabilities also benefit from the redundancy provided by an application that employs both audio and visual output.

In addition to making your application accessible, you should consider incorporating the following features:

• Provide options to adjust the length of expected response times. Users who have difficulty quickly responding to application events benefit from having extra time to respond.When a timed response is required—such as notification that a regularly scheduled action is about to take place—you should provide at least one response method that does not require users to respond within the timed interval. Alternatively, you should provide at least one method that allows users to adjust the response time to at least five times the default setting.

• Avoid using regularly blinking cursors or other objects on screen. The frequency of a blinking object must not be in the range of 2 hertz to 55 hertz, inclusive. Objects that blink in this frequency range can cause medical complications, such as seizures, in some people.

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