Human-Computer Interaction & Design¶

29 domain-specific abstractions whose origin domain is Human-Computer Interaction & Design.

Accessibility — The design commitment to keep a system perceivable, operable, understandable, and robust for the full distribution of intended users including the sensory, motor, cognitive, and infrastructural tails — by designing to those tails rather than to the median.
Cognitive Walkthrough — A usability-evaluation method in which an expert evaluator steps through a bounded task as a first-time user, asking four action-cycle questions at each step, so learnability breakdowns are localized to a specific step and broken link rather than yielding a holistic rating.
Direct Manipulation — Let a user control a system by physically acting on a continuously visible representation of the objects — dragging, resizing, pointing — with reversible actions and sub-100ms feedback, rather than issuing symbolic commands that name objects indirectly.
Discoverability — Measure the degree to which a system's actions and features can be located through perception and exploration alone — a property of the artifact, not the user — separating capability from findable capability and locating unfound features as a design defect.
Empty State Design — The UI practice of deliberately designing the zero-content view — treating it as a first-class state with a fixed four-slot template (message, intentionality cue, call-to-action, optional sample) rather than whatever the populated layout degrades to.
Focus-Order Failure — The accessibility defect in which an interface advances programmatic focus (Tab navigation, screen-reader linearization) in a sequence that diverges from the task's semantic order — invisible to visual review, and sometimes placing a confirmation control before the content it confirms.
Friction Budgeting — The design discipline of treating interaction cost as an explicit allocation variable rather than a uniform negative — concentrating load-bearing friction where it buys reflection, safety, or consent, and removing dead weight elsewhere, under a bounded user-tolerance budget.
Haitz's Law — The empirical LED regularity that light output per package rises ~20x per decade while cost per lumen falls ~10x — a log-linear trajectory arising because half a dozen loss terms improve multiplicatively, used as a roadmap and a below-trend diagnostic until efficiencies hit their thermodynamic ceilings.
Hazard-Control Decay — Track the widening gap between what a safety control's paperwork says it does and what it actually does under hazard, so that a control certified sound by audit can be found silently unprotective before it fails.
Keyboard Accessibility — The design property that every interactive function in a GUI can be operated with the keyboard alone — making the keyboard a channel-redundant, complete alternative to the pointer, and the upstream contract every assistive technology depends on.
Microcopy Ambiguity — The HCI failure where a terse interface label admits more than one reading, so the user decompresses it against a prior different from the designer's and acts correctly on the wrong interpretation.
Mode Error — The interaction failure in which the same user action is interpreted differently by a system depending on a hidden mode the user does not perceive — the user acts correctly for the mode they believe is active, and the system, in the actually active mode, does something else.
Motion-Triggered Harm — The inclusive-design failure in which interface animation, autoplay, parallax, or screen flash exceeds a susceptible user's physiological tolerance — a presentation channel that doubles as a harm channel, delivering an involuntary stimulus the median-calibrated design never accounted for.
Operable Design — The commitment that every action an artefact requires must have at least one operationally-equivalent alternative path across input modalities and motor envelopes, so users are not gated out by assumptions about how actions are performed.
Orientation Loss — Diagnose why a competent user gets lost by checking three location facts — where am I, what can I move to, how did I arrive — at each transition seam, reading the orientation state off the count of missing facts regardless of substrate.
Perceivable Design — Require that every essential signal an interface conveys be decoupled from any single sensory channel and offered through an alternative at sufficient fidelity, so a user shut out of one channel — vision, hearing — is not excluded.
Progress Indicator — A UI element that externalises a running process's position — how far along, how much remains, whether it is still alive — to resolve the uncertainty that would otherwise drive a waiting user to abandon or repeatedly check in.
Progressive-Disclosure Failure — Diagnose an interface's usability breakdowns as a single mistuning between its staging schedule and the readiness of the users and tasks it actually meets, read off by whether too much is hidden or too much exposed.
Protection Standard — Declare the named threshold up to which a system is designed to withstand a hazard class — which simultaneously frames every event above it as accepted residual risk, converting implicit unprotection into governed unprotection that can be audited, insured, and contested.
Repairability — The scored design property of a physical artefact measuring how cheaply and reliably a failed instance can be restored by component replacement rather than whole-unit replacement — a conjunction of accessible disassembly, modularity, documentation, parts availability, and software support.
Responsive-Layout Breakage — Diagnose the silent UI failure where an interface's content survives a viewport, device, or locale transformation but its layout-encoded meaning — priority, adjacency, hierarchy, above-the-fold prominence — is lost, so a passing content-accessibility check actively conceals the defect.
Robust Accessibility — Author web content so its load-bearing meaning lives in structural markup and the accessibility tree rather than in presentational accidents, so any current or future assistive technology — including ones the author cannot test against — can recover the intent through the same shared API.
Screen-Reader Ambiguity — An interface's visual structure carries semantic information never encoded into the machine-readable accessibility tree, so an assistive-technology user — navigating only that projection — encounters an interface stripped of the organization a sighted user relies on.
Touch Target Size — The HCI rule that interactive elements be large and well-spaced enough for the operating population's worst-case input precision to hit reliably — grounded in Fitts's Law and codified as platform minimums like 44pt or 48dp.
Touch-Target Miss — Reclassify a mistyped tap from operator error to interface defect by reading the miss rate off the mismatch between a control's target geometry and the operator population's motor precision — a geometric scan Fitts's Law makes quantitative.
User Journey — Represent a person's experience of a service as an ordered sequence of touchpoints, annotated stage by stage with goals, actions, channels, and an emotional curve, so that friction hidden by aggregate scores becomes visible and attributable to a specific design decision.
User-Centered Design — Focus on user needs.
Visibility of System Status — Keep users out of the dark by making a system's hidden internal state externally legible through timely, appropriately calibrated feedback — enumerating every state a user's actions can induce and asking, for each, whether the user can see they are in it in time to choose a next action.
Wayfinding System — A designed network of environmental cues on a legible substrate that lets a goal-directed agent localise, choose a next step, and recover from disorientation — pushing navigation work out of the head into the environment.