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Human Factors focuses on designing system interfaces to optimize the user’s ability to accomplish tasks successfully and error-free within a reasonable time period. It is an applied science with roots in understanding how people use tools, with the dual mission of enhancing performance while also minimizing the risk of human error, injury or frustration. Ergonomics is often used interchangably with human factors, and indeed the key professional society for the field is the Human Factors and Ergonomics Society (HFES) However, in general, ergnonomics has had roots that are closer to biomechanics and injury analysis, while the roots of human factors are more in psychophysical task analysis. This is reflected academically, as most strong ergonomics programs have their roots in engineering departments and occupational health, while most strong human factors have their roots in psychology departments or industrial engineering departments that have a history of tight ties to the military or NASA. Usability refers to the extent to which a product can be used by specified users to achieve specified goals in an effective and efficient manner, to the satisfaction of these users. In recent years this term has taken on great significance within industry, and terms such as usability engineering and user-centered design are now in common use. Many companies designing consumer products now have in-house usability labs. Practical components of a user-oriented design include:
In recent years there has been increasing use of computers within society, including the clinical environment. Much of the target of usability activity the design of human-computer interaction (HCI) and interface design, especially as related to optimizing human performance and ease of use. Accessibility addresses access to effective use of a product by all people, including persons with disabilities. Accessible design targets removing barriers that prevent the person from participating in the use of a product, i.e. extending a design to maximize the number of potential customers who can readily use the device or service. While there is often synergy with usability (e.g., ease of use is desirable) and accessibility is sometimes considered a category of usability, at times making an interface more fully accessible may lower the degree of usability for some. For instance, an interface may appear more complex when multimodal options are added that make it accessible to more people. Multimodality refers to support for transformations to alternative sensory interface modes for a channel (e.g., between text and speech), such that more than one modality is available. There are two basic strategies for enhancing access: "direct access" (direct adaptations to product designs that significantly include their accessibility) and "assistive access" (product interface(s) that enable(s) an add-on assistive technology to provide the user with access). Legislation such as Section 508 of the Rehab Act allows either strategy. Universal Design is the design of products and environments to be effectively and efficiently usable by people with a wide range of abilities, to the greatest extend possible, without the need for adaptation or specialized design. It clearly relates to usability and accessibility, with the concept of universal usability, i.e. usable by all, fitting well with the concept of univeral design. Indeed, the Universal Design Performance Measures for products can be viewed as a tool for assessing universal usability. While the terms usability, accessibility and universal design all involve levels of degree, in the limit they converge. In my opinion the most general term is Universal Access in that it includes the barriers of distance and time as well as a universally designed and usable interface.
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