Spring 2008 6.831 User Interface Design and Implementation 1Lecture 24: Accessibility Today’s Topics• Kinds of impairments• Assistive technology• Accessibility guidelinesSpring 2008 6.831 User Interface Design and Implementation 2 Today’s lecture is about accessibility, which generally means making it possible for users with impairments to use a graphical user interface. We’ll talk about the kinds of impairments we’ll be concerned with; the technology (both software and hardware) that help users deal with them; and some guidelines for designing UIs for accessibility. Diversity of Ability• Visual impairments– Color perception– Acuity (“legal blindness”)– Total blindness• Hearing impairments– Often varies with frequency• Motor disabilities– Tremor and spasms– Muscle weakness and fatigue– ParalysisSpring 2008 6.831 User Interface Design and Implementation 3 We’ll focus on physical impairments for this lecture, specifically problems in vision, hearing, or motor control, because that’s how “accessibility” is generally understood. But note that there are other impairments that are relevant to making a user interface usable by a wide spectrum of people. Some have cognitive disabilities, like difficulty learning or paying attention. Others have difficulty reading, either because they never learned or because they read a language different from yours. (We’ll talk about this last one in the internationalization lecture coming up.) We’ve talked about one form of vision impairment already: color blindness. Even more common than that, of course, is impaired visual acuity, i.e. inability to focus clearly. For most people, visual acuity problems can be corrected with glasses or contact lenses, but some haveuncorrectably bad vision. Roughly a million Americans are legally blind (unable to read even the biggest letter on an eye chart, even with corrective lenses). Perhaps 10% of them are totally blind, unable to sense light at all. Hearing impairments affect the ability to sense sound intensity, and range in a spectrum from reduced sensitivity to complete loss. Hearing impairments often depend on sound frequency; a person may hear lower frequencies well, but not high frequencies. Motor disabilities come in many different forms, and have many different causes. Sufferers of cerebral palsy experience uncontrollable tremors and spasms, making it difficult to make fine motor movements. Muscular dystrophy and multiple sclerosis can make muscles weak, and sufferers may tire easily when doing repeated or large muscle movements. Neural damage can cause complete paralysis of limbs. Impairments Affect Everybody• Aging– Reduced visual acuity– Hearing loss– Arthritis• Overexposure– Noise-induced hearing loss–RSI• Situational disabilities– Driving a car– Walking down the street– In a noisy environmentSpring 2008 6.831 User Interface Design and Implementation 4 But physical impairments, or their effects, aren’t limited to people with congenital diseases or trauma. Aging causes all three kinds of impairments. We’ve already discussed some of the impacts of aging on color vision. Older adults may also have reduced acuity, reduced hearing, and reduced mobility (specifically arthritis, which involves tremors, pain, and fatigue). Overuse can also cause impairment to younger people, as if aging prematurely. Most people don’t blind themselves by staring at the sun, but some lose their hearing prematurely by working in extremely loud environments (or listening to iPods?). Repetitive stress injury (RSI) is a motor impairment caused by excessive computer use (among other activities), with symptoms including pain, numbness, and weakness. Finally, all of us can experience situational disabilities: temporary conditions of ourselves or our environment that effectively cause impairment. For example, when you’re driving a car, your handsand eyes are occupied with the driving task, so with respect to an in-dashboard computer, you’re experiencing visual and motor impairments. Similarly, when you’re walking down the street, your visual abilities are diminished (because you have to watch where you’re going), and your ability to do fine motor control is reduced as well (because every step jars your entire body). In a noisy environment (say, the deck of an aircraft carrier), you can’t hear. When the sunlight is glaring on your laptop screen, you can’t see. The take-away message from this is that impairments affect everybody, and vision, hearing, and motor lie on a spectrum of ability that varies widely between users and over time. So we should take them into account when we’re designing. Universal Design• Equitable use• Flexibility in use• Simple & intuitive• Perceptible information• Tolerance for error• Low physical effort• Size and space forapproach and useSpring 2008 6.831 User Interface Design and Implementation 5 Universal design is a school of thought that takes this fact explicitly to heart, by seeking to design for all users, across as much of the spectrum of capability as possible. Contrast this with the attitude that is implicit in this class, and in most actual design, where we mainly design for the typical user, and then (8 weeks into the course?) discuss how to make it “accessible” to everybody else. Universal design challenges us to think about supporting a wide range of capability from the start. The proponents of Universal Design (http://www.design.ncsu.edu/cud/) have put forth seven guiding principles, listed here. Several are already familiar to us (simplicity, learnability, visibility, errors), and several are more relevant mainly to physical design (effort, size, space). But the first principle is the heart of the universal design philosophy: equitable use. As much as possible, all users should have the same interface, so that groups with differing abilities are not stigmatized. (If the identical interface isn’t possible, then provide equivalent interfaces.) Good universal designs are not dumbed down to make them universal; you shouldn’t sacrifice efficiency or flexibility for typical users in order to enable users with reduced ability. Instead, a good universal design has features that make the design better for everyone. Classic examples are kitchentools with fat, textured handles (like the vegetable peeler shown here); not only are they easier for arthritis
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