Glossary

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Photoparoxysmal Response(also: PPR, Photosensitive Response)

An abnormal brain response to flashing lights or patterns, detected through electroencephalogram (EEG) monitoring during intermittent photic stimulation. A photoparoxysmal response indicates photosensitivity and potential risk for photosensitive epilepsy, though not everyone who…

Photophobia(also: Light Sensitivity)

A genuine physiological sensitivity to bright light, flickering light, or intense visual patterns that causes symptoms such as headaches, migraines, nausea, dizziness, and disorientation. Despite its name suggesting a psychological fear, photophobia involves real neurological…

Photoplethysmography(also: PPG)

A non-invasive optical technique used to detect blood volume changes in peripheral circulation, commonly implemented in wearable devices like smartwatches and fitness trackers. PPG sensors use light (typically red and green LEDs) to measure how blood flow absorbs and reflects…

Photosensitive epilepsy(also: PSE, Photosensitivity, Visually-provoked epilepsy)

A form of epilepsy in which seizures are triggered by visual stimuli such as flashing lights, strobing effects, rapid colour transitions, or high-contrast repeating patterns. It affects approximately 3 to 5 percent of people with epilepsy and is more common in children and…

Photosensitivity(also: Photosensitive Epilepsy, PSE)

A neurological condition in which exposure to flickering light patterns, flashing graphics, or rapid luminance changes triggers physiological responses including seizures, migraines, nausea, dizziness, and disorientation. Photosensitive epilepsy, the most dangerous form, affects…

Photosensitivity(also: Light Sensitivity, Photophobia)

An abnormal sensitivity to light that can cause discomfort, pain, or visual disturbance. Photosensitivity affects many people with visual impairments and certain neurological conditions including migraine and epilepsy. In digital accessibility, photosensitivity considerations…

Phrase-Based Communication(also: Phrase-Based AAC, Pre-Stored Phrase Communication)

An augmentative and alternative communication approach where users select complete pre-composed phrases or sentences rather than constructing messages letter by letter or word by word. Phrase-based systems offer faster communication rates than spelling-based methods, which is…

Physical Accessibility(also: Physical Access, Architectural Accessibility)

Physical accessibility refers to the design of buildings, environments, and public spaces so they can be independently used by people with physical disabilities, including those who use mobility aids. It encompasses features such as ramps, elevators, accessible restrooms,…

Physical Agency(also: Bodily Agency, Sense of Agency)

The feeling of control and ownership over physical actions and their effects in the world. In assistive technology contexts, physical agency refers to a users sense of directly controlling objects and receiving sensory confirmation of their actions. Traditional AT designs often…

Physical Control(also: Direct Control, Direct Manipulation)

An interaction paradigm where the user directly manipulates on-screen objects or controls by pointing to them and acting on them, as with a mouse click or touch screen tap. In physical control, the focus or cursor moves among all visible interface elements, and the user must…

Physical Crowdsourcing(also: Spatial Crowdsourcing, Physical World Crowdsourcing)

A form of crowdsourcing in which tasks require participants to perform actions in the physical world rather than completing digital tasks online. In an accessibility context, physical crowdsourcing has been applied to installing and maintaining navigation infrastructure such as…

Physical Disability(also: Motor Disability, Physical Impairment)

A condition that affects a person's physical functioning, mobility, dexterity, or stamina. Physical disabilities include conditions such as paralysis, amputation, muscular dystrophy, cerebral palsy, spinal cord injury, multiple sclerosis, and arthritis. In technology and VR…

Physical Guidance(also: Hands-On Guidance, Physical Assistance)

A body movement teaching technique in which an instructor physically moves or positions a student's body to demonstrate correct form, rhythm, or placement. Physical guidance is widely used in teaching dance, sports, and martial arts to blind and low vision students, as it…

Physical Layer Accessibility

The dimension of VR accessibility concerned with whether users can physically access and operate VR hardware and interaction paradigms. This includes the setup process (putting on head-mounted displays, adjusting straps), manipulating controllers or using hand tracking, and…

Physical Rehabilitation(also: Physiotherapy, Physical Therapy)

A therapeutic process aimed at restoring, maintaining, or improving physical function, mobility, and strength through structured exercises and interventions. Physical rehabilitation is essential for people with motor disabilities, injuries, or neurological conditions to regain…

Physical Therapy(also: Physiotherapy, PT)

A healthcare profession focused on evaluating and treating physical impairments, functional limitations, and disabilities through movement, exercise, manual therapy, and assistive devices. Physical therapists work with people recovering from injuries, surgeries, strokes, and…

Physiological Computing(also: Biometric Computing, Biosignal-based Computing)

A computing paradigm that uses real-time physiological signals from the body to inform system responses and adaptations. Common signals include heart rate (via photoplethysmography), skin conductance (galvanic skin response), respiration, and brain activity (EEG). In…

Physiological Sensing(also: Biosensing)

Measuring bodily signals - such as heart rate, galvanic skin response, skin temperature, respiration, or muscle activity - to infer aspects of a user's physical or affective state. Physiological sensing is widely used in accessibility, affective computing, and digital health to…

Pico Projection(also: Pico Projector, Pocket Projector, Mini Projection)

A compact projection technology that enables small, portable devices to project images and information onto nearby surfaces. In accessibility contexts, pico projection offers an alternative to screen-based interfaces by allowing users to project communication props, maps,…

Pictograms(also: Pictogram, Picture Symbols, PCS)

Simplified pictorial symbols that represent concepts, objects, activities, emotions, or places, widely used as a form of augmentative and alternative communication (AAC) and as a visual support for autistic individuals, minimally verbal users, and people with cognitive…

Pictograph(also: Pictogram, Picture Symbol, Graphic Symbol)

A simplified visual symbol or image that represents a word, concept, or action, used as an alternative or supplement to written text. Pictograph systems such as Sclera, Beta, and Widgit are widely used in augmentative and alternative communication (AAC) to support people with…

Picture Communication Symbols(also: PCS, Boardmaker Symbols)

A widely used graphic symbol system for augmentative and alternative communication (AAC), consisting of simple, colorful line drawings representing words, phrases, and concepts. Developed by Mayer-Johnson (now part of Tobii Dynavox), PCS is one of the most common symbol sets…

Picture Exchange Communication System(also: PECS)

A structured augmentative and alternative communication (AAC) system that teaches individuals to use pictures to communicate with others. Developed by Andrew Bondy and Lori Frost in 1985, PECS uses a series of six phases to teach individuals — typically children with autism or…

Picture Prompting(also: Visual prompting, Pictorial instruction)

An instructional strategy that uses photographs or illustrations to depict how to complete each step of a task, providing visual guidance for people with developmental or intellectual disabilities. Picture prompts can be delivered through physical cards, printed instructions, or…

Picture Smart AI(also: JAWS Picture Smart AI)

Picture Smart AI is a feature of the JAWS screen reader (Freedom Scientific/Vispero) that uses multimodal AI models to describe images, charts, and on-screen content on demand. It can describe a photo, explain a chart, read text embedded in an image, or answer follow-up…

Picture-in-Picture(also: PiP, PIP)

A display technique that shows a smaller video or content window overlaid on the main content, allowing viewers to see two sources simultaneously. In accessibility contexts, picture-in-picture is the primary method for presenting sign language interpretation in video and…

Pidgin Signed English(also: PSE, Contact Signing, Sign Supported English)

A hybrid communication system that combines elements of American Sign Language (ASL) and English. In PSE, signers use ASL signs for the main content words of an English sentence, following English word order, but generally do not include extra signs for English word endings or…

Pie Menu(also: Radial Menu, Circular Menu)

A pie menu is a circular or ring-shaped menu interface in which command options are arranged radially around a central point, allowing selection by moving the cursor or making a directional gesture toward the desired item. Unlike linear drop-down menus, pie menus leverage…

Piezo Vibrator(also: Piezoelectric Vibrator, Piezoelectric Actuator)

A device that converts electrical signals into mechanical vibrations using the piezoelectric effect, commonly used in tactile displays and haptic feedback systems for assistive technology. Piezo vibrators can be arranged in arrays to create tactile patterns that convey spatial…

Piezoelectric Actuator(also: Piezo Actuator, Piezoelectric Bimorph)

A device that converts electrical energy into precise mechanical motion using the piezoelectric effect — the property of certain materials to change shape when an electric voltage is applied. In assistive technology, piezoelectric actuators are the dominant mechanism used in…

Piggyback Prototyping(also: piggyback prototype, parasitic prototyping)

Piggyback prototyping is a research methodology in which researchers add new features or interventions to already-deployed, live systems rather than building standalone prototypes, enabling study of user behaviour with novel features in authentic real-world contexts. The…

Pilot (Shared Control)

In shared-control video gaming, the pilot is the primary player — usually a person with a disability — who drives the gameplay and makes strategic decisions, while delegating specific inaccessible inputs to a copilot. The pilot retains leadership of the session and, in most…

Pilot-Passenger Model(also: Pilot/Passenger Framework)

A model describing household technology dynamics where "pilots" are the users who set up and configure devices, while "passengers" are those who simply use the systems configured for them. In disability contexts, disabled users may be forced into the passenger role due to…

Pin Array(also: Pin Matrix, Pin-Matrix Display)

A grid of individually controllable pins used in refreshable tactile displays to create tactile images and text. Each pin can be raised or lowered electronically, and in some displays raised to multiple heights, allowing the representation of graphical content through touch. Pin…

Pin Array Display(also: Pin Matrix Display, Tactile Pin Display)

A type of tactile display technology that uses an array of individually controllable pins that can be raised or lowered to create tactile patterns, textures, and graphics. Pin array displays are used in 2D tactile displays to present graphical information such as diagrams,…

Pin-Matrix Display(also: Tactile Pin Display, Pin Array Display, Two-Dimensional Braille Display)

A refreshable tactile display technology that uses a grid of individually controllable pins to create two-dimensional tactile images, as opposed to single-line refreshable Braille displays that show only one row of characters. Pin-matrix displays like the BrailleDis 7200 can…

Pitch

The perceived highness or lowness of a sound, determined primarily by its fundamental frequency (measured in Hertz). Pitch is one of the primary dimensions along which music and speech are organized, underpinning melody, harmony, and prosody. In accessibility work, pitch is…

Pitch Detection(also: Pitch Tracking, Fundamental Frequency Detection)

The computational process of determining the fundamental frequency (pitch) of an audio signal in real time. In accessibility, pitch detection is used in non-speech voice interfaces where changes in humming or vocal pitch are mapped to control commands — for example, a rising…

Pitch Mapping(also: Pitch-Y Mapping, Frequency Mapping)

A sonification technique that maps data values to auditory pitch, where higher values produce higher-pitched sounds and lower values produce lower-pitched sounds. In accessibility contexts, pitch mapping is commonly used to represent the vertical position (Y-axis) of data points…

Pitch Polarity(also: Pitch Mapping Direction)

The direction in which pitch changes correspond to navigation direction in an auditory interface — specifically, whether pitch increases (ascending polarity) or decreases (descending polarity) as a user scrolls downward through a list or menu. Pitch polarity is a design variable…

Pivotal Response Training(also: PRT, Pivotal Response Treatment)

A naturalistic, child-initiated behavioural intervention developed for children with autism that targets "pivotal" skills — foundational abilities whose improvement produces widespread positive changes across social, communication, and academic domains. Unlike highly structured…

Place Attachment(also: Sense of Place)

Place attachment is the emotional and cognitive bond a person forms with a particular location — a home, neighbourhood, city, or landscape — built up through memory, repeated experience, social ties, and meaning-making. It is studied in environmental psychology, urban planning,…

Plain Language(also: Plain English, Clear Language, Simple Language)

Plain language is communication that is clear, concise, and well-organized so that the intended audience can easily find, understand, and use the information. In accessibility, plain language is essential for making content accessible to people with cognitive disabilities, low…

Plain language(also: Plain English, Easy read, Simple language)

A communication approach that uses clear, concise, and well-organised writing designed to be understood the first time it is read. Plain language avoids jargon, complex sentence structures, and ambiguous wording. It is a key accessibility practice for making information…

Plan Recognition(also: Intent Prediction, Action Prediction)

A technique in human-computer interaction where a system predicts the user's intended action based on patterns in their input behaviour and the current interaction context. By anticipating what the user is likely to do next, the system can weight recognition processes…

Planning Fallacy

A well-documented cognitive bias, identified by Kahneman and Tversky and elaborated by Buehler and colleagues, in which people systematically underestimate how long their own tasks will take and overestimate how much they can finish, even when they have direct evidence that…

Platform Accessibility

The degree to which online platforms (websites, apps, social media, marketplace platforms) are usable by and inclusive of disabled people. Platform accessibility encompasses not only technical compliance with standards like WCAG but also policies, algorithms, and moderation…

Platform Governance(also: Social Media Governance)

Platform governance refers to the policies, rules, procedures, and technical mechanisms through which digital platforms regulate user behaviour, content, and participation. It encompasses both formal rule-making structures — such as community guidelines, terms of service,…

Play-by-Play(also: Play-by-play announcing, Play-by-play commentary)

In sports broadcasting, the moment-to-moment verbal description of on-screen action provided by the main commentator (e.g., who has the puck, who is passing to whom). Because play-by-play describes what sighted viewers can see, it largely duplicates visual information for Deaf…

Playback Speed(also: Video Speed, Playback Rate)

The rate at which video or audio content plays relative to its original recording speed. Most video platforms allow users to adjust playback speed, typically from 0.25x to 2x or higher. For viewers with ADHD, playback speed is an important accessibility feature—faster playback…