Glossary

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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…

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