Natural user interface

In computing, a natural user interface, or NUI, or natural interface is a user interface that is effectively invisible, and remains invisible as the user continuously learns increasingly complex interactions. The word natural is used because most computer interfaces use artificial control devices whose operation has to be learned.

A NUI relies on a user being able to quickly transition from novice to expert. While the interface requires learning, that learning is eased through design which gives the user the feeling that they are instantly and continuously successful. Thus, "natural" refers to a goal in the user experience – that the interaction comes naturally, while interacting with the technology, rather than that the interface itself is natural. This is contrasted with the idea of an intuitive interface, referring to one that can be used without previous learning.

Several design strategies have been proposed which have met this goal to varying degrees of success. One strategy is the use of a "reality user interface" ("RUI"), also known as "reality-based interfaces" (RBI) methods. One example of an RUI strategy is to use a wearable computer to render real-world objects "clickable", i.e. so that the wearer can click on any everyday object so as to make it function as a hyperlink, thus merging cyberspace and the real world. Because the term "natural" is evocative of the "natural world", RBI are often confused for NUI, when in fact they are merely one means of achieving it.

One example of a strategy for designing a NUI not based in RBI is the strict limiting of functionality and customization, so that users have very little to learn in the operation of a device. Provided that the default capabilities match the user's goals, the interface is effortless to use. This is an overarching design strategy in Apple's iOS. Because this design is coincident with a direct-touch display, non-designers commonly misattribute the effortlessness of interacting with the device to that multi-touch display, and not to the design of the software where it actually resides.

In the 1990s, Steve Mann developed a number of user-interface strategies using natural interaction with the real world as an alternative to a command-line interface (CLI) or graphical user interface (GUI). Mann referred to this work as "natural user interfaces", "Direct User Interfaces", and "metaphor-free computing". Mann's EyeTap technology typically embodies an example of a natural user interface. Mann's use of the word "Natural" refers to both action that comes naturally to human users, as well as the use of nature itself, i.e. physics (Natural Philosophy), and the natural environment. A good example of an NUI in both these senses is the hydraulophone, especially when it is used as an input device, in which touching a natural element (water) becomes a way of inputting data. More generally, a class of musical instruments called "physiphones", so-named from the Greek words "physika", "physikos" (nature) and "phone" (sound) have also been proposed as "Nature-based user interfaces".

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