Glossary

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AI transparency(also: Algorithmic transparency, Model transparency)

The practice of making artificial intelligence systems understandable to users and stakeholders, including how they work, what data they use, and the confidence levels of their outputs. For assistive technology users, AI transparency enables informed decision-making about when…

Above the Fold(also: Above-the-fold, First Screen Content)

Content that is visible on a web page without requiring the user to scroll. The term originates from newspaper publishing where important headlines appeared above the physical fold of the paper. In digital accessibility and usability, above-the-fold placement is significant…

Accessibility Feature Discovery(also: Feature Discoverability, Accessibility Settings Discovery)

The process by which users become aware of, find, understand, and adopt accessibility features and settings available on their devices or in software. Research consistently shows that many users who could benefit from accessibility features are unaware they exist, cannot find…

Accessibility Heuristics(also: Accessibility Heuristic Evaluation)

A set of broad usability and accessibility principles used to evaluate digital products for barriers that may prevent people with disabilities from using them effectively. Unlike detailed technical checklists such as WCAG success criteria, accessibility heuristics provide…

Caption Flow(also: Captioning Flow, Text Flow)

The smoothness and regularity with which caption text appears and updates on screen during real-time captioning. Good caption flow means text arrives at a consistent pace without jarring delays, sudden bursts, or choppy delivery. Research shows that caption flow significantly…

CogTool

A cognitive modeling tool developed at Carnegie Mellon University that generates quantitative predictions of human task performance times based on the Keystroke-Level Model (KLM) and the ACT-R cognitive architecture. Designers create storyboards of user interface screens and…

Cognitive Load(also: Mental Load, Cognitive Demand)

The total amount of mental effort required to complete a task, encompassing the processing, storage, and management of information in working memory. Cognitive load theory distinguishes between intrinsic load (inherent task complexity), extraneous load (unnecessary complexity…

Cognitive Usability

The extent to which a system, interface, or information resource can be effectively used by people with varying cognitive abilities and processing styles. Cognitive usability goes beyond traditional usability measures (efficiency, effectiveness, satisfaction) to specifically…

Cognitive Walkthrough(also: Expert Walkthrough)

An accessibility and usability evaluation method in which one or more experts step through a series of tasks from the perspective of a target user, identifying potential barriers and difficulties at each step. In accessibility evaluations, cognitive walkthroughs often involve…

Content Filtering(also: Content Adaptation, Adaptive Content Delivery)

The process of selectively displaying or hiding portions of digital content based on user preferences, roles, device capabilities, or accessibility needs. In an accessibility context, content filtering allows users to control the level of detail they receive, reducing…

Context of Use(also: Use Context, Usage Context)

The combination of users, tasks, equipment (hardware, software, and materials), and the physical and social environments in which a product or service is used. In accessibility, context of use is a critical consideration because the same website may present different barriers…

Cursor Ambiguity(also: Cursor Position Ambiguity)

The difficulty users experience in determining the exact position of the text cursor, particularly when using screen readers on touchscreen devices. Screen readers announce the character or word at the cursor location, but users may not know whether the cursor is at the…

Customization Paradox(also: Paradox of Choice in Customization)

The phenomenon where providing more customization options to reduce barriers paradoxically creates new barriers through increased cognitive load, decision fatigue, and distraction from the customization interface itself. The customization paradox is particularly acute for ADHD…

Decision Fatigue(also: Choice Overload, Decision Exhaustion)

The deteriorating quality of decisions made by an individual after a long session of decision-making, or when confronted with too many choices simultaneously. Decision fatigue disproportionately affects people with executive dysfunction, ADHD, and other cognitive disabilities,…

Discoverability(also: Feature Discoverability)

The degree to which a user can find and become aware of a feature, setting, or capability within a system. In accessibility, discoverability is a critical challenge because users who could benefit from accessibility features — such as screen magnification, high contrast modes,…

Ecological validity(also: Real-world validity)

The degree to which research findings from controlled laboratory settings accurately reflect behaviour and performance in real-world everyday contexts. In accessibility research, ecological validity is a critical concern because laboratory conditions — structured tasks, quiet…

Error correction strategy(also: Text correction, Input error recovery)

The methods and behaviours users employ to detect and fix errors during text input, including backspace deletion, cursor repositioning, autocorrect, and retyping. For blind and visually impaired users, error correction is disproportionately costly because detecting errors…

Fitts' Law(also: Fitts Law)

A predictive model of human movement in human-computer interaction that states the time required to move to a target area is a function of the distance to the target and the size of the target. Specifically, larger and closer targets are faster to acquire than smaller and more…

Fitts's Law(also: Fitts Law)

A predictive model of human movement that describes the time required to rapidly move to a target area as a function of the distance to the target and the size of the target. Formulated by Paul Fitts in 1954, the law states that movement time increases logarithmically as the…

Fitts's Law(also: Fitts Law, Fitts' Law)

A predictive model of human movement that describes the time required to rapidly move to a target area as a function of the distance to the target and the target's size. Smaller and more distant targets take longer to reach and are more prone to errors. In accessibility, Fitts's…

Formative Evaluation(also: Formative Usability Testing, Formative Assessment)

Usability evaluation conducted early in the design process using prototypes, mockups, or wireframes to identify design problems and inform improvements. Formative testing is qualitative and iterative, focusing on understanding user behavior and identifying issues rather than…

GOMS(also: Goals, Operators, Methods, and Selection rules, KLM, Keystroke-Level Model)

A family of human-computer interaction models used to predict how long it will take a user to complete a task with a given interface. GOMS stands for Goals, Operators, Methods, and Selection rules — the four components used to describe user behavior. The simplest variant, the…

Gesture vocabulary(also: Gesture set, Interaction gesture repertoire)

The complete set of touch gestures recognized and used by a device or application, including single-stroke gestures (swipes, flicks), multistroke gestures (multi-tap, draw-then-tap), and multitouch gestures (pinch, rotate, two-finger swipe). As touchscreen interfaces evolve,…

HHS Usability Guidelines(also: Research-Based Web Design and Usability Guidelines, Usability.gov Guidelines)

A comprehensive set of evidence-based web design and usability guidelines published by the U.S. Department of Health and Human Services (HHS). The guidelines cover areas including homepage design, page layout, navigation, scrolling, headings, links, text appearance, content…

Heuristic Walkthrough(also: Heuristic walk-through)

A usability evaluation method proposed by Andrew Sears (1997) that combines scenario-based cognitive walkthrough with heuristic evaluation. Evaluators work through realistic user tasks using a prioritised list of heuristics, surfacing both task-specific and general usability…

Human Factors Engineering(also: Ergonomics, Human Factors)

The scientific discipline concerned with designing systems, products, and environments to be compatible with the physical and cognitive capabilities and limitations of the people who use them. In accessibility, human factors engineering applies usability methods and techniques —…

ISO 9241-210(also: Human-Centred Design Standard, Ergonomics of Human-System Interaction — Part 210)

An international standard specifying the principles and activities of human-centred design (HCD) for interactive systems. It defines a six-step iterative process — understanding context of use, specifying user requirements, producing design solutions, and evaluating against…

Information Transfer Rate(also: ITR, Data Transfer Rate)

A measure of the speed and accuracy with which a user can communicate information to a computer through an input device, typically expressed in bits per second. Information transfer rate accounts for both the size of the input vocabulary (how many possible commands exist) and…

Input Exertion(also: Input Effort, Interaction Cost)

The physical and cognitive effort required to provide input to a digital system, including keystrokes, mouse movements, taps, and voice commands. For people with motor impairments, input exertion is a critical accessibility concern because even small inefficiencies — such as…

Jakob's Law(also: Jakobs Law, Law of Familiarity)

A usability heuristic coined by Jakob Nielsen stating that users spend most of their time on other sites and expect your site to work like the ones they already know. Accessibility implication: novel interaction patterns impose higher cognitive load than familiar ones, so…

Keystroke-Level Model(also: KLM)

A simplified predictive model from human-computer interaction research, originally developed by Card, Moran, and Newell, that estimates task completion time by decomposing user interactions into elementary operations such as keystrokes, pointing movements, mouse clicks, and…

Keystrokes Per Character(also: KSPC)

A metric used to evaluate the efficiency of text-entry methods by measuring the average number of keystrokes required to produce each character of text. A lower KSPC indicates a more efficient input method. For standard MultiTap on a 12-key phone keypad, the theoretical best…

Latency(also: Delay, Lag, Response Time)

The time delay between when an event occurs and when its accessible representation is delivered to the user. In real-time captioning, latency is the gap between spoken words and their appearance as text, typically measured in seconds. In screen readers and other assistive…

Learnability

A usability attribute measuring how easy it is for users to accomplish basic tasks the first time they encounter a design. High learnability means new users can quickly become productive with a system. For accessibility, learnability is particularly important because users with…

Material Experience(also: Material Aesthetics, Material Interaction)

The multidimensional way people perceive, interpret, and emotionally respond to the physical materials of objects they interact with. The materials experience framework categorizes these experiences into four levels: sensorial (immediate physical sensations from touching,…

Mental Fatigue(also: Cognitive Fatigue, Mental Exhaustion)

A state of reduced cognitive capacity resulting from prolonged mental effort, characterized by difficulty concentrating, slower processing, increased errors, and reduced ability to handle unexpected situations. Mental fatigue particularly affects people with dementia, traumatic…

Mental Workload(also: Cognitive Load, Cognitive Workload)

The amount of cognitive effort and mental resources required to complete a task. In accessibility contexts, mental workload is an important measure of how demanding an interface is to use — an interface may be technically functional but impose excessive cognitive burden on users…

Menu Selection(also: Menu Navigation, Menu Selection Task)

A fundamental computer interaction task in which a user chooses an option from a set of items presented in a menu structure, typically involving locating the target item, moving the cursor to it, and clicking to select. Menu selection performance is commonly measured by task…

Midas Touch Effect(also: Midas Touch Problem)

An interaction design challenge in touch-based and gesture-based interfaces where the system cannot distinguish between intentional activation commands and incidental or exploratory touches. Named after the mythological King Midas whose touch turned everything to gold, the…

Multi-Layered Interface(also: ML Interface, Layered Interface, Training Wheels Interface)

An interface design approach where novice users start with a reduced-functionality layer containing only basic features, then progress to more complex layers as they become comfortable. This technique reduces cognitive load during initial learning by limiting the number of…

NASA Task Load Index(also: NASA-TLX, Task Load Index)

A widely used subjective workload assessment tool developed by NASA that measures perceived workload across six dimensions: mental demand, physical demand, temporal demand, performance, effort, and frustration. Participants rate each dimension on a scale, providing a…

NASA Task Load Index(also: NASA-TLX, TLX)

A widely used subjective workload assessment tool developed by NASA that measures perceived workload across six dimensions: mental demand, physical demand, temporal demand, performance, effort, and frustration. In accessibility research, NASA-TLX is frequently employed to…

NGOMSL(also: Natural GOMS Language)

A structured notation for writing GOMS (Goals, Operators, Methods, Selection rules) models in a program-like form that is readable by humans. NGOMSL was developed by David Kieras as a more formal variant of GOMS that includes selection rules and allows operators at the keystroke…

Navigability(also: Ease of Navigation, Web Navigability)

The ease and efficiency with which a user can move through a web page, application, or document to reach their intended content. For accessibility practice, navigability is a primary determinant of whether a screen-reader, voice-browser, or keyboard-only user can actually…

Novelty Effect(also: Novelty bias)

A research-methodology concept describing the tendency for users to behave differently with a new technology simply because it is new, rather than because of its enduring value. Novelty effects inflate short-term engagement, enthusiasm, and usage, then fade as the technology…

Overshoot(also: Cursor Overshoot, Target Overshoot)

In pointing device interaction, the phenomenon where the cursor travels beyond the intended target before the user can stop it, requiring corrective movements back toward the target. Overshoot is measured as the maximum distance traveled beyond the target as a percentage of the…

Procedural task analysis(also: Task decomposition, Step-by-step analysis)

A method of breaking down complex tasks into sequential, discrete steps to understand user workflows and identify points of difficulty. In accessibility contexts, procedural task analysis reveals where users with cognitive, sensory, or motor impairments encounter barriers — such…

Progressive Disclosure(also: Staged Disclosure, Layered Interface)

An interaction design pattern that initially presents only the most essential options or information, revealing additional complexity progressively as users need or request it. Progressive disclosure reduces cognitive load and visual clutter by avoiding overwhelming users with…

Psychometric Evaluation(also: Psychometric Validation, Psychometric Analysis)

The process of assessing whether a measurement instrument (such as a questionnaire or survey) possesses desirable statistical properties including validity, reliability, and consistency. In accessibility and usability research, psychometric evaluation is used to determine…

Reaching Time(also: Navigation Time, Time to Target)

A usability metric measuring the time required for a user to navigate to a specific element on a web page. For blind users employing screen readers, reaching time is a key indicator of page navigability and efficiency, as it captures the cumulative cost of navigating through and…