Glossary

Search results

Achromatopsia(also: Rod Monochromacy, Total Color Blindness, Complete Achromatopsia)

A rare inherited vision condition in which a person has little or no ability to perceive color, seeing the world primarily in shades of grey. People with achromatopsia typically also experience light sensitivity (photophobia), reduced visual acuity, and involuntary eye movements…

Age-Related Dexterity Changes(also: Motor Decline in Aging, Age-Related Motor Impairment)

The gradual decline in fine motor control, hand-eye coordination, and manual dexterity that commonly occurs with aging, affecting the ability to use input devices like mice, keyboards, and touchscreens. These changes are caused by factors including reduced spatial abilities,…

Age-Related Functional Limitations(also: Ageing-Related Accessibility Needs, Age-Related Impairments)

The gradual changes in sensory, motor, and cognitive abilities that commonly occur with ageing, including declining vision, hearing loss, reduced dexterity and fine motor control, and changes in memory and processing speed. These functional limitations often overlap…

Age-Related Impairment(also: Age-Related Decline, Aging-Related Disability)

Functional limitations that commonly develop with advancing age, often involving multiple interacting mild impairments rather than a single major disability. Age-related impairments may affect vision (presbyopia, reduced contrast sensitivity, cataracts), hearing (presbycusis),…

Age-Related Vision Loss(also: Age-Related Visual Impairment)

Vision impairment that occurs as a consequence of aging, representing the most common cause of blindness and low vision worldwide. Conditions include age-related macular degeneration, glaucoma, diabetic retinopathy, and cataracts. The prevalence of significant visual impairment…

Akinesia(also: Poverty of Movement)

The loss or impairment of the ability to initiate voluntary movement, distinct from muscle weakness or paralysis. In Parkinson's Disease, akinesia manifests as difficulty starting movements, reduced spontaneous movements like blinking or arm swing while walking, and a mask-like…

Albinism(also: Oculocutaneous Albinism, Ocular Albinism)

A group of inherited conditions characterized by reduced or absent melanin pigment production, affecting the skin, hair, and eyes. Ocular effects commonly include reduced visual acuity, nystagmus (involuntary eye movements), photophobia (light sensitivity), and reduced depth…

Amnesia(also: Memory Loss, Amnestic Disorder)

A neurological condition characterised by the partial or complete inability to recall past experiences (retrograde amnesia) or to form new memories (anterograde amnesia). Amnesia results from damage to brain structures responsible for memory processing, commonly caused by…

Aniridia

A rare congenital eye condition involving the partial or complete absence of the iris, often accompanied by reduced visual acuity, light sensitivity (photophobia), nystagmus, and sometimes glaucoma or cataracts. Digital accommodations typically include high screen brightness…

Anomalous Trichromat(also: Anomalous Trichromacy, Colour Anomaly)

A person who has all three types of cone cells in the retina but one type has a shifted spectral sensitivity, causing altered colour perception that is less severe than dichromacy. Anomalous trichromats include protanomalous individuals (shifted L-cones, reduced red…

Anterograde Amnesia

A form of amnesia in which a person is unable to form new memories following the onset of the condition, while memories from before the injury or illness may remain largely intact. Anterograde amnesia typically results from damage to the hippocampus or surrounding medial…

Articulation Disorder(also: speech sound disorder, phonological disorder)

A speech impairment characterized by difficulty producing speech sounds or phonemes correctly. Articulation disorders are classified into three categories: organic (caused by hearing loss or structural abnormalities), motor (caused by neurological conditions affecting motor…

Asperger Syndrome(also: Asperger's Syndrome, AS, Asperger's Disorder)

A neurodevelopmental condition previously classified as a distinct diagnosis within the autism spectrum, characterized by difficulties with social interaction and nonverbal communication, alongside restricted and repetitive patterns of behavior and interests. Unlike autistic…

Athetoid(also: Athetosis, Athetoid Movement)

A type of involuntary movement characterised by slow, continuous, writhing motions, particularly affecting the hands, fingers, and face. Athetoid movements are commonly associated with athetoid cerebral palsy, a subtype of cerebral palsy that results from damage to the basal…

Athetoid Cerebral Palsy(also: dyskinetic cerebral palsy, athetosis)

A type of cerebral palsy characterized by involuntary, slow, writhing movements (athetosis) that affect the face, trunk, and limbs. It accounts for about 10-15% of cerebral palsy cases and results from damage to the basal ganglia. People with athetoid cerebral palsy often…

Athetoid Cerebral Palsy(also: Dyskinetic Cerebral Palsy, Athetosis)

A form of cerebral palsy characterized by involuntary, uncontrolled, slow writhing movements, particularly affecting the hands, feet, arms, and legs, and sometimes the muscles of the face and tongue. Athetoid cerebral palsy results from damage to the basal ganglia and is…

Autism Diagnostic Observation Schedule(also: ADOS, ADOS-2)

A standardized diagnostic protocol for autism that uses structured and semi-structured social interaction tasks between an examiner and the person being assessed. First published in 1989 and designed based on a sample of children aged 6-18, it was followed by a second edition…

Autism Spectrum Disorder(also: ASD, Autism)

A neurodevelopmental condition characterized by differences in social communication, sensory processing, and patterns of behavior or interests. Autism exists on a spectrum, meaning it presents differently across individuals — some may have significant support needs while others…

Avoidance Behaviour(also: Avoidance Behaviors, Covert Stuttering)

Strategies used by people who stutter to conceal or prevent stuttering events, including substituting feared words with easier alternatives, talking around a word (circumlocution), using filler words to delay, avoiding certain speaking situations entirely, or pretending to have…

Becker Muscular Dystrophy(also: BMD)

A genetic neuromuscular disorder caused by mutations in the dystrophin gene on the X chromosome, resulting in progressive muscle weakness and wasting. Becker Muscular Dystrophy is similar to Duchenne Muscular Dystrophy but generally has a later onset (typically in the teens or…

Blue Cone Monochromatism(also: BCM, S-cone Monochromacy)

A rare inherited vision condition in which only the blue (short-wavelength) cones function, resulting in severely reduced color vision, reduced visual acuity, photophobia, and nystagmus. Affected individuals see the world in shades of blue and yellow and typically benefit from…

Borderline Intellectual Functioning(also: BIF, borderline intellectual disability, slow learners)

A condition describing individuals with IQ scores roughly between 70 and 85—above the diagnostic threshold for intellectual disability (IQ below 70) but below the neurotypical range. Representing about 13.6% of the general population, BIF individuals typically have working…

Bradykinesia(also: Slowness of Movement)

Bradykinesia is a motor symptom characterized by slowness of movement and a progressive reduction in the speed and amplitude of repetitive actions. It is one of the cardinal symptoms of Parkinson's disease and directly affects a person's ability to interact with digital devices…

Challenging Behavior(also: Problem Behavior, Behaviors of Concern)

Actions by individuals with intellectual or developmental disabilities that pose risks to themselves or others, or significantly interfere with daily activities and learning. In the context of autism, challenging behaviors are often classified into categories such as…

Chiari Malformation(also: Arnold-Chiari Malformation)

A structural condition in which brain tissue extends into the spinal canal, which can cause a range of neurological symptoms including headaches, balance issues, and vision problems such as blurred or double vision, nystagmus, and reduced contrast sensitivity. Digital…

Co-contraction(also: Unintended Co-contraction, Muscle Co-activation)

The simultaneous activation of antagonistic muscles — for example, the biceps and triceps firing at the same time. Some co-contraction is normal and useful for joint stability, but involuntary or excessive co-contraction is common in conditions such as spasticity, cerebral…

Co-morbidity(also: Comorbidity, Co-occurring Conditions, Multiple Disabilities)

The simultaneous presence of two or more medical conditions or disabilities in a single individual. In accessibility contexts, co-morbidity is a critical design consideration because many users, particularly older adults, experience multiple impairments simultaneously — for…

Cognitive Disability(also: Cognitive Impairment, Intellectual and Cognitive Disability)

A broad category of disabilities affecting cognitive functions such as memory, attention, problem-solving, reading, language comprehension, and executive function. Cognitive disabilities can be developmental (such as Down Syndrome or Autism Spectrum Disorder), acquired (such as…

Cognitive Dysfunction(also: Cognitive Impairment, Cognitive Disability)

A broad term encompassing conditions that affect cognitive functions such as memory, attention, problem-solving, learning, language, and executive function. Cognitive dysfunction ranges from mild impairments (age-related memory decline, mild cognitive impairment) to major…

Cone Dystrophy(also: Cone-Rod Dystrophy)

A group of inherited eye disorders that affect the cone cells in the retina, which are responsible for color vision, central vision, and visual acuity in well-lit conditions. People with cone dystrophy typically experience progressive loss of color vision, decreased visual…

Dementia

A group of progressive neurological conditions that affect memory, thinking, orientation, comprehension, language, and judgment. Alzheimer's disease is the most common form. Dementia significantly impacts how people interact with digital technology, often requiring simplified…

Developmental Apraxia of Speech(also: Childhood Apraxia of Speech, CAS, DAS)

A motor speech disorder in which children have difficulty planning and coordinating the movements needed for speech, despite having no muscle weakness. Children with developmental apraxia of speech know what they want to say but their brains have difficulty coordinating the…

Developmental Delay(also: Developmental Disability, Global Developmental Delay)

A condition in which a child does not reach developmental milestones — such as motor skills, speech, social skills, or cognitive abilities — at the expected ages. Developmental delay may affect one or multiple areas of development and can be caused by genetic conditions,…

Dichromat(also: Dichromacy, Dichromatic Vision)

A person with colour vision based on only two types of functional cone cells in the retina instead of the typical three, resulting in a reduced ability to distinguish certain colours. Dichromats perceive colour in a two-dimensional colour space rather than the three-dimensional…

Disfluency(also: Dysfluency, Speech Disfluency)

Any interruption or break in the normal flow of speech, including repetitions, prolongations, blocks, interjections (such as "um" or "uh"), and revisions. While all speakers experience occasional disfluencies, their frequency and severity distinguish typical speech from…

Distractibility(also: Attentional Distractibility, Susceptibility to Distraction)

A cognitive characteristic in which a person has difficulty maintaining focus on a task due to sensitivity to irrelevant stimuli in their environment. Distractibility is a feature of many conditions including ADHD, autism, dyslexia, and traumatic brain injury, and can also be…

Down Syndrome(also: Trisomy 21)

A genetic condition caused by the presence of an extra copy of chromosome 21, resulting in varying degrees of intellectual and developmental differences. People with Down Syndrome may experience challenges with memory, attention, language processing, and fine motor skills that…

Dysarthric Speech(also: Dysarthria)

Dysarthric speech is speech that is affected by dysarthria, a motor speech disorder resulting from neurological injury or conditions that affect the muscles used for speech production. Characteristics include imprecise articulation, irregular speech rate, abnormal pitch and…

Dyskinesia(also: Levodopa-Induced Dyskinesia, LID)

A movement disorder characterized by involuntary, uncontrollable movements such as twitching, swaying, or jerking, most commonly associated with long-term use of levodopa medication for Parkinson's disease. Dyskinesia can significantly affect a person's ability to use standard…

Dystonia(also: Dystonic Movements)

A movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements, postures, or both. Dystonia can affect a single body part (focal dystonia), adjacent regions (segmental), or the whole body (generalized). In…

Fetal Alcohol Spectrum Disorder(also: FASD, Fetal Alcohol Syndrome, FAS)

A group of conditions that can occur in a person whose mother consumed alcohol during pregnancy. Effects can include physical, behavioral, and learning problems, with a wide range of severity. FASD is relevant to digital accessibility because individuals may experience cognitive…

Fine Motor Skills(also: Fine Motor Control, Dexterity)

The ability to make precise, coordinated movements using the small muscles of the hands, fingers, and wrists. Fine motor skills are essential for tasks such as typing, using a mouse, performing touch gestures, and operating physical controls on devices. Many people with…

Fragile X Syndrome(also: FXS, Martin-Bell Syndrome)

A genetic condition caused by a mutation in the FMR1 gene on the X chromosome, making it the most common inherited cause of intellectual disability and the most common known single-gene cause of autism spectrum disorder. Fragile X affects males more severely than females, with…

Freezing of Gait(also: FOG, Gait Freezing, Motor Blocks)

A common and debilitating symptom of Parkinson's Disease in which a person suddenly and temporarily feels as though their feet are glued to the floor, despite intending to walk. Freezing episodes typically last seconds to minutes and are a major cause of falls and loss of…

Hydrocephalus(also: Hydrocephaly, Water on the Brain)

A condition characterized by an abnormal accumulation of cerebrospinal fluid within the ventricles of the brain, causing increased intracranial pressure and enlargement of the head. Hydrocephalus can be congenital or acquired, and if untreated can lead to developmental delays,…

Hyperopia(also: Farsightedness, Long-Sightedness, Hypermetropia)

A refractive error in which the eye focuses light behind the retina rather than on it, causing near objects to appear blurred while distant objects may remain relatively clear. Hyperopia occurs when the eyeball is too short or the cornea is insufficiently curved. It is…

Hypotonia(also: Low Muscle Tone, Muscle Hypotonia, Floppy Muscle Syndrome)

A condition characterized by decreased muscle tone, resulting in reduced resistance to passive movement and often affecting posture and motor control. Hypotonia is common in many developmental disabilities including Down syndrome, cerebral palsy, and various genetic conditions.…

Intellectual Disability(also: ID, Learning Disability (UK), Cognitive Disability)

A condition characterized by significant limitations in both intellectual functioning (reasoning, learning, problem-solving) and adaptive behavior (conceptual, social, and practical skills) that originates before age 22. The DSM-5 and ICD-11 classify severity levels based on…

Keratoconus

A progressive eye condition in which the normally round cornea thins and bulges into a cone-like shape, causing irregular astigmatism and significant visual distortion that cannot be fully corrected with standard glasses or contact lenses. Keratoconus typically begins in…

Language-Based Learning Impairment(also: LLI, Language Learning Impairment, Language Learning Disability)

A developmental condition in which children have difficulty acquiring language and later reading skills while other cognitive abilities appear relatively intact. Language-based learning impairments affect an estimated 20% of preschool and school-aged children, and more than 50%…