Glossary

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Eyelid Gesture(also: Eyelid Interaction, Eyelid-Based Input)

An eyelid gesture is a deliberate eye movement used as an input method for controlling digital devices, involving intentional opening and closing of one or both eyelids in specific patterns, sequences, and durations. Unlike simple blink detection, eyelid gestures exploit the…

Face Tracking(also: Facial Tracking, Face Detection and Tracking)

A computer vision technology that detects and follows the position and movement of a user's face in real time using a camera or depth sensor. In accessibility, face tracking enables hands-free computer interaction for people with motor disabilities who cannot use traditional…

Facial Action Unit(also: Action Unit, AU, FACS Action Unit)

A component of the Facial Action Coding System (FACS) that represents a specific movement or position of facial muscles. Each action unit corresponds to a distinct facial movement, such as raising the inner eyebrow (AU1) or pulling the lip corner (AU12 for smiling). In…

Facial Gesture Recognition(also: Face Tracking, Facial Expression Recognition)

Technology that uses cameras and computer vision algorithms to detect and interpret facial movements and expressions in real time. For accessibility, facial gestures such as opening the mouth, raising eyebrows, smiling, or nose movements can be mapped to computer commands,…

Finger Tracking(also: Fingertip Tracking, Finger Detection, Hand Tracking)

Computer vision or sensor-based technology that detects and follows the position and movement of a user's fingers in real-time. In accessibility applications, finger tracking enables hands-free interaction with tactile graphics, touchscreens, and physical objects by monitoring…

Fitts's Law(also: Fitts Law)

Fitts's law is 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. Widely used in human-computer interaction (HCI) since the 1970s, it quantifies pointing…

Foot-Based Interaction(also: Foot Input, Foot Gesture Interaction)

An interaction technique that uses foot movements and gestures as input for controlling digital devices. Foot-based interaction is particularly relevant for people with upper body motor impairments who have functional lower limbs but cannot use their hands, including people with…

Force Feedback Joystick(also: Haptic Joystick, Rumble Joystick)

An input device that combines a traditional joystick with motors or actuators that apply physical resistance, vibration, or directional forces to the user's hand, providing tactile information about the virtual environment being navigated. In accessibility applications, force…

Gaze(also: Eye Gaze, Gaze Direction, Point of Regard)

The direction in which a person is looking, typically measured as the point of visual fixation on a display or in a physical environment. Gaze tracking technology captures where users look and for how long, enabling gaze-based input for motor-impaired users who cannot use…

Gaze Fixation(also: Eye Fixation, Visual Fixation)

The act of maintaining one's gaze steadily on a specific point or target, as opposed to saccadic eye movements between points. In gaze-based assistive technology, gaze fixation is the primary mechanism for making selections — users fixate on a desired target for a set dwell time…

Gaze Input(also: Eye Tracking Input, Gaze-Based Interaction, Eye Control)

An input method that uses eye-tracking technology to detect where a user is looking, enabling interaction with digital interfaces through eye movements such as fixation (dwelling on a target), smooth pursuit (following a moving target), or blinks. Gaze input is a critical…

Gaze Interaction(also: Gaze-Based Interaction, Gaze Input, Eye Gaze Control)

Gaze interaction is a method of controlling computers and devices by tracking where a person is looking on the screen. Using eye-tracking technology, the system detects the user's point of gaze and translates it into cursor movement or selection actions, often combined with…

Gaze-Based Interaction(also: Gaze Input, Eye-Gaze Interaction, Gaze Control)

An interaction method where users control digital interfaces by directing their visual gaze at on-screen targets, typically detected through eye tracking or head orientation tracking. In accessibility contexts, gaze-based interaction provides an alternative input modality for…

Gazepoint(also: Gaze Point, Point of Gaze)

The specific point on a screen or surface where a person is looking at any given moment, as determined by an eye tracking system. The gazepoint is calculated from the gaze vector — the line extending from the eye to the display — and is typically reported as x,y coordinates. Eye…

Gestural Input(also: Gesture-based Input, Touch Gestures)

Input methods that interpret finger movements on a touchscreen as commands, including taps, swipes, pinches, and multi-finger gestures. For blind users, gestural input must be performed without visual feedback, requiring consistent gesture recognition regardless of screen…

Gestural Interaction(also: Gesture-Based Interaction)

A mode of human-computer interaction in which users control systems through movements of the body — hands, arms, head, eyes, or whole body — captured by sensors such as accelerometers, cameras, IMUs, or depth sensors. Gestural interaction supports hands-free or low-force control…

Gesture Input(also: Gesture Recognition, Gesture-Based Interaction)

An input method that uses physical movements of the body — typically hands, fingers, arms, or head — to interact with digital systems. Gesture input includes touchscreen gestures (swipes, taps, pinches), mid-air gestures detected by cameras or motion sensors, and motion gestures…

Gesture Interaction(also: Gesture-based interaction, Gestural interfaces)

An input modality in which users control digital systems through hand, arm, or body movements detected by cameras, depth sensors, IMUs, or wearable devices rather than through traditional keyboards, pointing devices, or touchscreens. Gesture interaction underpins many augmented…

Gesture Recognition(also: Gesture Detection)

The computational process of identifying and interpreting human gestures—typically hand, arm, or body movements—using sensors and machine learning algorithms. Gesture recognition systems analyze data from cameras, accelerometers, gyroscopes, or other sensors to classify…

Gesture Typing(also: Swipe Typing, Trace Typing, Glide Typing)

A text entry method on touchscreen devices where the user enters a word by continuously gliding their finger from letter to letter on a virtual keyboard without lifting it, rather than tapping each key individually. The continuous trace is interpreted by a statistical decoder…

Gesture-Based Input(also: Gesture input, Gestural input, Gesture-based text entry)

An input method that interprets finger or hand movements — such as swipes, taps, and drawn paths — as commands or text characters. For people with visual impairments, gesture-based input on touchscreens offers an alternative to traditional keyboard layouts that require targeting…

Gesture-Based Interface(also: Gestural Interface, Gesture Recognition Interface)

An interaction system that interprets human gestures—such as hand movements, body poses, or finger motions—as input commands. Gesture-based interfaces can use cameras, accelerometers, touch surfaces, or wearable sensors to detect and interpret movement. In accessibility, they…

Goal Crossing(also: Crossing-Based Input, Crossing Interface)

An input technique where users select targets by moving through a boundary line rather than clicking within a target area. Research shows goal crossing can improve input performance for people with motor impairments by reducing the precision demands of target acquisition—users…

Grasp Recognition

Technology that detects and interprets how a user holds, grips, or manipulates objects, typically through sensors in VR controllers or camera-based hand tracking. In VR accessibility, grasp recognition is relevant because it can enable more natural object manipulation in virtual…

Grid-Based Cursor Control(also: Grid-Based Navigation, Grid Overlay Navigation)

A hands-free cursor positioning technique that overlays a numbered grid on the screen, allowing users to select a cell by voice command or other input to recursively zoom into smaller screen regions until the desired target is reached. Grid-based approaches reduce the vocabulary…

Hand Tracking(also: Gesture Tracking, Hand Gesture Recognition)

A technology that detects and tracks the position, orientation, and movements of a user's hands and fingers without requiring physical controllers, typically using cameras and computer vision algorithms. In extended reality, hand tracking enables hands-free interaction through…

Hands-Free Interaction(also: Hands-Free Computing, No-Hands Input, Hands-free)

The ability to operate digital devices and interfaces without using the hands, typically through voice commands, eye tracking, head movements, foot controls, or brain-computer interfaces. Hands-free interaction is critical for users with upper limb motor impairments,…

Hands-Free Interface(also: Hands-Free Computing, Hands-Free Input)

A hands-free interface is a computer interaction system that does not require the use of hands or fingers, enabling users to control software through alternative input channels such as head movements, eye gaze, voice commands, foot pedals, or breath-controlled switches. These…

Haptic Input(also: Haptic Interaction, Touch Input)

Haptic input refers to interaction methods that use the sense of touch to communicate information between a user and a computer system. This includes devices such as data gloves, force-feedback controllers, and touch-sensitive surfaces that detect hand movements, gestures, and…

Head Pointing(also: Head-Controlled Pointing, Head Mouse)

Head pointing is an alternative input method that maps head movements to cursor position on a computer screen, enabling hands-free mouse control. The user moves their head to direct the cursor, with the system translating head orientation or position into screen coordinates.…

Head Tracking(also: Head Movement Tracking, Head-Controlled Input, Head Tracker)

An assistive technology input method that translates natural head movements into computer cursor control or other input actions. Head tracking systems use cameras, infrared sensors, or depth sensors to detect head position and orientation, allowing users with limited or no hand…

Head-based Pointing(also: Head Tracking, Head Mouse, Head-controlled Input)

An alternative input method that allows users to control an on-screen cursor by moving their head, typically tracked via a camera, infrared sensor, or inertial measurement unit. Head-based pointing is particularly valuable for people with motor impairments who cannot use…

Humming Interface(also: Control-by-Humming, Hum-Based Interface)

A human-computer interaction method that uses hummed pitch patterns as control signals for operating devices. In a humming interface, a pitch detection algorithm analyses the user's hummed input, segments it into discrete notes based on pitch contour (rising, falling, or flat),…

Impulse Engine(also: Impulse Engine 3000)

The Impulse Engine 3000 was a force-feedback haptic device manufactured by Immersion Corporation in the 1990s, used for research into haptic interfaces and virtual reality. The device featured a probe that users manipulated in three degrees of freedom (forward/backward, up/down,…

Index of Difficulty(also: ID, Fitts ID)

The Index of Difficulty (ID) is the central quantity in Fitts' law that captures how hard a rapid aimed pointing movement is, computed as log₂(A/W + 1) in the Shannon formulation, where A is the amplitude (distance to the target) and W is the target width along the movement…

Input Method Editor(also: IME, Input Method)

A software component that allows users to enter characters and symbols not directly available on their physical keyboard, particularly for languages with large character sets or complex scripts. IMEs are essential for typing in languages like Chinese, Japanese, Korean, and…

Input Modality(also: Interaction Modality, Input Method)

A distinct channel or method through which a user provides input to a computing system, such as touch, voice, gesture, gaze, or keyboard interaction. In accessibility contexts, supporting multiple input modalities is critical because users with different disabilities may need…

Input Rate(also: Keystroke Rate)

The speed at which a user can produce individual keystrokes or character inputs, typically measured in seconds per keystroke. Input rate varies dramatically across access methods: touch typists may achieve 0.1-0.2 seconds per keystroke, while users of switch scanning systems or…

Integrated Control System(also: Integrated Control)

An assistive technology approach where a single input device serves multiple control functions, such as wheelchair navigation, mouse cursor control, and text entry. Integrated control systems reduce the number of separate devices a person with a disability must manage, lowering…

Isometric Gesture(also: Isometric Contraction Gesture)

An isometric gesture is a gesture in which a person activates their muscles without producing visible movement — the body position remains static while muscle tension changes. This contrasts with isotonic gestures, where visible hand or arm movement occurs over time. Isometric…

Isotonic Joystick(also: Displacement Joystick, Free-Moving Joystick)

An isotonic joystick is a type of joystick input device that moves freely in response to applied force and returns to a centre position when released. Unlike isometric (force-sensing) joysticks that remain stationary and measure the pressure applied, isotonic joysticks…

Key Acceptance Delay(also: Acceptance Delay, Key Debounce)

A keyboard accessibility setting that requires a key to be held down for a specified minimum duration before it is registered as a deliberate press. Keys released before the delay period expires are ignored, filtering out brief accidental touches. Key acceptance delay is the…

Key Remapping(also: Key Rebinding, Control Remapping, Custom Key Bindings)

The ability to reassign keyboard controls to different keys than the software defaults. Key remapping is essential for users with motor disabilities who may only be able to reach certain areas of the keyboard, use one hand, or have limited range of motion. For example, a…

Keyboard Navigation(also: Keyboard Access, Keyboard Operability)

The ability to use all features and functions of a website, application, or software using only the keyboard, without requiring a mouse or other pointing device. Keyboard navigation is essential for people who are blind and use screen readers, people with motor disabilities who…

Keyguard(also: Keyboard Guard, Key Guard)

A rigid cover that fits over a keyboard with holes aligned to each key, allowing users with motor impairments to rest their hands on the surface without accidentally pressing keys. Keyguards help people who have imprecise motor control, tremors, or involuntary movements to type…

Linear Scanning(also: Row-column scanning, Automatic scanning)

An input method for AAC devices and on-screen keyboards where selections are highlighted sequentially, typically row by row and then item by item, allowing users with severe motor impairments to select options using a single switch. The system automatically moves through options…

Microswitch(also: Micro-switch, Assistive Switch)

A small, sensitive switch used in assistive technology that can be activated by minimal physical movement such as a light touch, head turn, or muscle contraction. Microswitches are used to provide environmental control and communication access for people with severe motor…

Mid-Air Gesture(also: In-Air Gesture, Free-Space Gesture)

A hand or arm movement performed in three-dimensional space, away from any surface, that is recognized by sensors as a command input. Mid-air gestures can be detected using cameras, depth sensors, or inertial measurement units in wearable devices like smartwatches. In…

Midas Touch Problem(also: Midas Touch Effect)

The Midas Touch problem is a well-known challenge in gaze-based and dwell-time-based computer interfaces where everything the user looks at or pauses the cursor over is interpreted as a selection command. Named after King Midas who turned everything he touched to gold, the…

Motion Sensor(also: Motion Detection, Gesture Sensor)

A device that detects physical movement in its environment, often by tracking body position, joint angles, or gestures. In accessibility and assistive technology, motion sensors enable touchless interaction, gesture-based interfaces, and movement-tracking rehabilitation systems.…