User Interface
Definition
A user interface is the boundary at which a person and a system meet — everything through which a person issues intentions to a machine and perceives what it has done. It is not a layer on top of a system; it is the only part of the system most people will ever encounter, and therefore, for practical purposes, it is the system.
Kinds
- Command-line interface (CLI). Text in, text out. Precise, composable, scriptable, and unforgiving of anyone who does not already know the vocabulary — a very wide gulf of execution traded for expert speed.
- Graphical user interface (GUI). Windows, icons, menus, pointer. Developed at Xerox PARC in the 1970s from Engelbart's work. Its achievement is recognition over recall: options are visible rather than remembered.
- Touch interface. Direct manipulation with the hand, removing the pointer as an intermediary — and removing hover, which had been carrying a great deal of the GUI's discoverability.
- Voice and conversational interface. No visible option set at all, which makes discovery the central unsolved problem: a system that can do a thousand things and shows none of them.
- Tangible interface. Physical objects whose arrangement is the state of the system.
- Ambient and peripheral interface. Information rendered at the edge of attention rather than in the centre. See calm technology and sonic metadata.
- Zero interface. Systems that act on inference without being addressed. The interface has not disappeared; it has become unavailable for inspection or correction.
Core Principles
- Visibility. Available actions and current state should be perceptible. See affordance and signifiers.
- Feedback. Every action gets a prompt, legible response.
- Consistency. Similar things behave similarly, within the system and with conventions outside it.
- Mapping. Controls relate to effects in a way that requires no memorisation.
- Constraints and error tolerance. Make wrong actions hard, and make them recoverable when they happen.
- Recognition over recall. Show, do not require remembering.
What an Interface Encodes
The design decisions in an interface are not neutral, and this is the part usually left out of accounts of usability.
An interface encodes a model of the user: what they are assumed to know, want, and be capable of. It encodes an allocation of effort: every step the designer did not simplify is work performed by every user, forever, and invisible in any accounting of the system's cost. It encodes a default, which is the single most consequential thing in any interface, because most people accept it. And it encodes a set of interests — where the operator's goals and the user's diverge, the asymmetry shows up as friction applied in one direction and removed in the other. See frictional interface and enshittification.
Relevance to Cyborg Anthropology
The interface is the seam this field studies. It is where a human competence meets a machine capability, and where the two are either joined well enough that the tool disappears into use — Merleau-Ponty's cane, Clark's transparency — or badly enough that the person spends their attention operating the tool instead of doing the thing.
Interfaces are also the most widely installed cognitive infrastructure ever built. The file, the folder, the desktop, the trash, the window, the feed and the undo command are metaphors that a few hundred people chose, and that several billion now think with. See Lakoff on why that matters.
