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…

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…

Part-of-Speech Tagging(also: POS Tagging, Grammatical Tagging)

Part-of-speech tagging is the natural-language-processing task of labelling each word in a text with its grammatical category — noun, verb, adjective, and so on — using context from surrounding words. Classical approaches use hidden Markov models with the Viterbi algorithm;…

Particle Filtering(also: Sequential Monte Carlo, Particle Filter)

Particle filtering is a probabilistic localization technique that estimates a user's position by maintaining a cloud of weighted "particles," each representing a possible location. As new sensor data arrives—from GPS, inertial sensors, or other sources—particles are updated,…

Pattern Recognition

A branch of machine learning and artificial intelligence focused on identifying regularities, patterns, and structures in data such as images, sounds, or sensor readings. In accessibility, pattern recognition is fundamental to technologies like sign language recognition systems…

Perceptual Linear Prediction(also: PLP, PLP Coefficients)

Perceptual Linear Prediction (PLP) is an acoustic feature extraction technique used in speech processing that models human auditory perception. PLP analysis applies psychoacoustic principles including critical band frequency resolution, equal-loudness pre-emphasis, and…

Perplexity(also: Language Model Perplexity)

A standard metric for evaluating language models that measures how well the model predicts a sample of text. Mathematically, perplexity is the inverse probability of the test set, normalised by the number of words — a lower perplexity indicates that the model assigns higher…

Pointwise Mutual Information(also: PMI)

A statistical measure used in natural language processing to quantify the strength of association between two words based on how much more frequently they co-occur in a corpus than would be expected by chance. PMI is calculated as the logarithm of the ratio of the observed…

Polar Motion Profile(also: PMP)

A Polar Motion Profile (PMP) is a computational technique used in sign language detection that models the quantity and distribution of motion relative to a detected face using polar coordinates. The method captures the characteristic hand and arm movements associated with…

Pose estimation(also: Body pose estimation, Human pose estimation)

The computational process of determining the position and orientation of a person's body joints and limbs from sensor data such as cameras, depth sensors, or inertial measurement units. In accessibility contexts, pose estimation enables applications like gesture-based…

Principal Component Analysis(also: PCA)

A statistical technique that reduces the dimensionality of data by identifying the principal axes of variation in a dataset. In accessibility and assistive technology contexts, PCA is commonly used in face recognition systems (as the basis of the Eigenfaces method), gesture…

Privacy-Enhancing Data Filters(also: Privacy Filters, Data Obfuscation Filters)

Visual or data modifications applied to training datasets that obscure the identity of contributors while preserving the information needed for machine learning tasks. In the context of sign language video, these filters may include face blurring, cel shading, avatar…

Project Sidewalk

An open-source web-based crowdsourcing tool developed at the University of Washington that enables volunteers to virtually audit sidewalk accessibility using Google Street View panoramas. Contributors label four types of accessibility features and problems: curb ramps, missing…

Prompt engineering(also: Prompt design, Prompt crafting)

The practice of designing and iteratively refining natural language inputs to large language models to elicit more accurate, relevant, or useful responses. In accessibility contexts, prompt engineering is an emerging skill that enables disabled users to customise AI interactions…

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