Glossary

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POMDP(also: Partially Observable Markov Decision Process)

A Partially Observable Markov Decision Process (POMDP) is a mathematical framework for modelling decision-making in situations where an agent cannot fully observe the state of its environment. In accessibility research, POMDPs are used to model how people with visual impairments…

POUR

The four foundational principles of WCAG: Perceivable (information must be presentable to users in ways they can perceive), Operable (user interface components must be operable), Understandable (information and operation of the user interface must be understandable), and Robust…

POUR Principles(also: POUR, Four Principles of Accessibility)

The four foundational principles of the Web Content Accessibility Guidelines (WCAG): Perceivable, Operable, Understandable, and Robust. Perceivable means information must be presentable in ways users can perceive (e.g., alt text for images, captions for video). Operable means…

PRISMA(also: Preferred Reporting Items for Systematic Reviews and Meta-Analyses)

A standardized methodology and reporting guideline for conducting systematic literature reviews and meta-analyses. PRISMA provides a structured framework including a checklist and flow diagram that documents how studies are identified, screened, assessed for eligibility, and…

PRISMA-ScR(also: PRISMA Extension for Scoping Reviews)

PRISMA-ScR is the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews - a 20-item checklist and flow diagram that standardises how scoping reviews are reported. It adapts the PRISMA framework (designed for systematic reviews) to the…

PS5 Access Controller(also: PlayStation Access Controller, Access Controller)

Sony's highly customisable controller for PlayStation 5, released in 2023 and designed for players with limited motor control. It has a flat disc layout with interchangeable button caps and analog stick attachments, 3.5 mm expansion ports for external switches, and…

PTSD(also: Post-traumatic stress disorder, Post-traumatic stress)

A psychiatric condition that can develop after exposure to traumatic events, characterized by intrusive memories, avoidance of trauma-related stimuli, negative changes in mood and cognition, and heightened arousal responses including hypervigilance and exaggerated startle. In…

PVI(also: People with Visual Impairments, Person with Visual Impairment, Persons with Visual Impairments)

An abbreviation widely used in HCI and accessibility research for "people with visual impairments," a person-first umbrella term that includes people who are blind, legally blind, or have low vision. PVI is often used interchangeably with BVI ("blind and visually impaired") and…

Pa11y

An open-source automated accessibility testing tool that runs from the command line and in continuous-integration pipelines. Pa11y can drive either axe-core or HTML CodeSniffer as its underlying rule engine, returning JSON-formatted results classified by severity (critical,…

Pacing Aid(also: Pacing System, Time Management Aid)

An assistive technology that helps individuals with cognitive impairments manage the timing and sequence of activities in daily routines. Pacing aids provide cues — visual, auditory, or tactile — to indicate whether the user is on schedule, ahead, or behind, without requiring…

Packet Loss(also: Network Packet Loss, Data Loss)

The failure of data packets to reach their destination during network transmission, common in VoIP and mobile telephony. Packet loss causes audio dropouts, distortion, and reduced intelligibility. Research shows that 20% packet loss can render voice telephony essentially…

Page Fragmentation(also: Visual Fragmentation, Content Fragmentation)

A web accessibility problem where different types of content on a web page (news articles, advertisements, navigation menus, related links) are visually grouped using colours, spacing, images, and layout but lack structural markup that would allow non-visual users to identify…

Page Landmarks(also: ARIA Landmarks, Landmark Regions, Landmark Roles)

Named regions of a web page that identify its high-level structure — for example banner, navigation, main, complementary, search, form, contentinfo — so that assistive technology can expose them as jump targets. Landmarks are typically declared with semantic HTML elements…

Page Linearization(also: Content Linearization, DOM Linearization, Source Order)

The process by which screen readers and other assistive technologies present web page content as a sequential, one-dimensional stream of text, typically following the order of elements in the HTML source code. Since web pages are designed as two-dimensional visual layouts where…

Page Magnification(also: Page Zoom, Web Page Magnification)

An accessibility feature that enlarges the entire visual presentation of a web page, including text, images, and layout elements, to make content easier to see for people with low vision or visual fatigue. Unlike text-only size increases, page magnification scales all page…

Page Sampling(also: Page Selection Strategy, Website Sampling)

The methodology used to select which pages within a website will be evaluated during an accessibility assessment. Common strategies include evaluating only the home page, testing specific page types (login, contact, sitemap), using hierarchical depth-based selection, or the…

Page Segmentation(also: Web Page Segmentation, VIPS)

The process of dividing a web page into distinct visual or structural blocks based on layout cues such as whitespace, borders, colors, and font properties. Page segmentation algorithms like Vision Based Page Segmentation (VIPS) analyze the rendered appearance of pages to…

Page Structure Preservation(also: Layout Preservation, Structure Retention)

The principle of maintaining the original spatial layout and DOM structure of a webpage when applying accessibility enhancements, content filtering, or other modifications. Preserving page structure ensures that users' mental models of familiar websites remain intact, that…

Page Turner(also: Page Turning Aid)

Any device, tool, or person that assists a musician in turning the pages of a music score during performance. Traditional page turners are human assistants who sit beside a musician and turn pages on cue. Technological alternatives include Bluetooth foot pedals for digital…

Pain Communication(also: pain expression, communicating pain)

The verbal and non-verbal processes through which a person conveys their pain experience to others, including family members, carers, and healthcare professionals. Chronic pain presents particular communication challenges because it is inherently subjective and invisible, often…

Pain Invalidation(also: chronic pain disbelief, pain dismissal)

The experience of having one's pain dismissed, disbelieved, or minimised by others, including healthcare professionals, family members, and social contacts. Pain invalidation is a pervasive barrier for people with chronic pain conditions, particularly primary pain syndromes such…

Pain Self-Management(also: chronic pain self-management)

A person-centred approach to living with chronic pain in which the individual takes an active role in managing their own condition through daily coping strategies, behavioural adaptations, and use of support resources, rather than relying solely on clinical interventions. Pain…

Pair Programming(also: Paired Programming, PP)

A software development practice where two programmers work together at one workstation, with one writing code (the "driver") and the other reviewing each line as it is typed (the "navigator" or "observer"). The two developers switch roles frequently. Pair programming promotes…

Palm Drawing(also: Palm Mapping, Palm Tracing)

A technique used by Orientation and Mobility (O&M) specialists to teach routes to people who are blind or have low vision. The instructor holds the person's palm face up and traces the path of a route with their finger while simultaneously providing verbal instructions. This…

Panel Transition Cue(also: Scene Transition Cue, Panel Change Signal)

An auditory signal used in audio-described comics and webtoons to indicate that the narrative has moved to a new panel, scene, or page. Panel transition cues help visually impaired listeners maintain orientation within the sequential narrative structure of comics, where visual…

Panning(also: Screen Panning, Viewport Panning)

The act of moving the visible area of a screen magnifier or viewport across a webpage or application to view content that extends beyond the currently displayed portion. For screen-magnifier users, panning is a fundamental but often arduous interaction technique, requiring…

Pantograph(also: Haptic Pantograph)

A haptic input device that allows users to explore a two-dimensional surface by physically moving a stylus or finger pad across an exploration area, while receiving tactile feedback from an attached tactile display. In accessibility applications, the pantograph enables people…

Paper Prototyping(also: Lo-Fi Prototyping, Low-Fidelity Prototyping)

A rapid design technique that uses paper, cardboard, and other simple materials to create tangible representations of product concepts before investing in digital or electronic implementation. Paper prototyping allows designers and users to quickly explore form, layout, and…

Para Powerlifting(also: Adaptive Powerlifting, Paralympic Powerlifting)

A Paralympic strength sport in which athletes with physical disabilities perform bench press lifts. Unlike able-bodied powerlifting which includes squat, bench press, and deadlift, para powerlifting focuses solely on the bench press to accommodate athletes with lower limb…

Para-Athlete(also: Disabled Athlete, Adaptive Athlete)

An athlete with a disability who competes in adaptive or Paralympic sports. Para-athletes may have physical disabilities (amputations, spinal cord injuries, cerebral palsy), visual impairments, or intellectual disabilities. They compete using adaptive equipment such as…

Paradox of the Active User

The Paradox of the Active User, identified by Carroll and Rosson (1987), refers to the observation that computer users systematically avoid investing time in learning more efficient tools or methods, even when doing so would yield significant long-term productivity gains. Users…

Paralinguistic Cues(also: Paralanguage, Paralinguistic Features, Non-verbal Vocal Cues)

Aspects of spoken communication that carry meaning beyond the literal words themselves: tone of voice, pitch contour, loudness, rhythm, tempo, stress, pauses, and voice quality. Paralinguistic cues convey emotion, emphasis, sarcasm, uncertainty, speaker identity, and social…

Paralinguistic Features(also: Prosodic Cues, Non-Verbal Speech Features)

Aspects of spoken communication that convey meaning beyond the literal words, including pitch, loudness, rhythm, tone, and emotional affect. These features are critical for understanding speaker intent, sarcasm, emphasis, and emotional state but are typically lost in standard…

Parallax(also: Visual Parallax, Binocular Parallax)

Parallax is the apparent displacement or difference in position of an object when viewed from two different vantage points. In human vision, binocular parallax — the slight difference between the images seen by each eye due to their spatial separation — is a primary cue for…

Parallel Play(also: Parallel Activity)

A form of social interaction where individuals engage in separate activities alongside each other without direct interaction. Originally described in child development research by Mildred Parten in 1932, parallel play has been recognized in neurodivergent communities as a…

Parallel Viewing(also: Dual-Screen Viewing)

A media consumption strategy in which viewers use a second screen alongside the primary display to access supplementary information, accessibility features, or alternative content representations without interrupting the main viewing experience. For people with disabilities,…

Paralympic(also: Paralympic Games, Paralympics)

The international multi-sport event for athletes with physical, visual, and intellectual disabilities, organized in parallel with the Olympic Games. The first organized Paralympic Games took place in 1948, with official recognition beginning in 1960. The Paralympic movement…

Paralysis(also: Paralyzed, Paresis)

The partial or complete loss of voluntary muscle function, resulting from damage to the motor nervous system. Common causes include spinal cord injury, stroke, traumatic brain injury, motor neuron diseases such as ALS, multiple sclerosis, cerebral palsy, and brainstem lesions…

Parameter Mapping Sonification(also: Parameter Mapping, Auditory Parameter Mapping)

A sonification technique that represents changes in data dimensions through corresponding changes in auditory dimensions such as pitch, loudness, timbre, spatial position (panning), tempo, or reverberation. Unlike auditory icons (which use recognizable real-world sounds) or…

Parameter-Efficient Fine-Tuning(also: PEFT, Lightweight Fine-Tuning)

Parameter-efficient fine-tuning is a family of techniques (LoRA, adapters, prefix tuning, prompt tuning) that adapt a large pretrained model to a new task or domain by updating only a small fraction of its parameters - typically under 1% - while freezing the rest. This…

Parametric design(also: Parametric modeling)

A design approach in which objects are defined by adjustable parameters (dimensions, angles, ratios) rather than direct geometric manipulation, allowing users to customize designs by changing numerical values without needing 3D modeling expertise. Parametric design is…

Paraplegia

A condition resulting from injury to the thoracic, lumbar, or sacral segments of the spinal cord, causing partial or complete loss of motor function and sensation in the legs, pelvis, and trunk while arm and hand function is preserved. People with paraplegia can typically use…

Parasocial Relationship(also: Parasocial Tie, Parasocial Interaction)

A parasocial relationship is a one-sided emotional bond that a media audience forms with a performer, creator, or online personality — the viewer feels a sense of friendship, loyalty, and familiarity despite no reciprocal awareness. In accessibility contexts, parasocial ties are…

Paratransit(also: Demand-responsive transit, Dial-a-ride)

A flexible, on-demand public transportation service that provides rides to people with disabilities who are unable to use fixed-route bus or rail systems. In the United States, the Americans with Disabilities Act requires transit agencies to offer complementary paratransit…

Parcel Locker(also: Package Locker, Smart Locker, Delivery Locker)

A self-service pickup cabinet where e-commerce parcels are deposited by couriers and retrieved by recipients using a code, QR scan, or mobile-app unlock. Parcel lockers are increasingly mandatory in apartment buildings and urban fulfilment networks. Accessibility barriers are…

Parents with Visual Impairments(also: PVI, Blind Parents, Visually Impaired Parents)

Parents with visual impairments (PVI) are blind or low-vision adults raising children, who are often sighted. PVI face distinctive parenting challenges that go beyond individual functional compensation: supporting children's visually-driven exploration (pointing, gaze, shared…

Paresis(also: Partial Paralysis)

A partial loss of voluntary muscle movement, distinguished from full paralysis (plegia). Paresis can affect a single limb (monoparesis), one side of the body (hemiparesis), or all four limbs (tetraparesis), and may result from stroke, cerebral palsy, spinal cord injury, or…

Pareto Principle(also: 80/20 Rule, Law of the Vital Few)

The empirical observation, named after economist Vilfredo Pareto, that in many systems roughly 80% of effects come from 20% of causes. In crowdsourcing and volunteer communities, the principle predicts that a small number of top contributors produce the majority of output, while…

Parkinson's Disease(also: PD)

A progressive neurodegenerative disorder affecting movement, including tremor, rigidity, slowness of movement, and balance problems. Parkinson's disease can also significantly affect speech (causing quiet, monotone, or slurred speech), facial expression, and fine motor control.…

Parkinsonian Tremor(also: Rest Tremor, Parkinson Tremor)

Parkinsonian tremor is an involuntary, rhythmic shaking that occurs primarily at rest and is associated with Parkinson's disease. It is caused by the reciprocal activation of antagonistic muscle groups and typically has a frequency of 4-6 Hz with a harmonic frequency…