Speech sound disorders and mutism

Why it matters

Speech and language conditions create barriers in environments that require verbal communication — voice interfaces, phone-based services, and customer service interactions. Understanding the distinction between different speech disorders helps practitioners match the right AT or communication strategy to the person’s actual need. (BoK p. 15)

Speech vs. language

These are related but distinct:

• Speech disorders affect the production of sounds — the physical act of forming and expressing words.
• Language disorders affect comprehension or formulation of meaning — understanding or constructing words and sentences. (Language disorders are covered in the next lesson.)

A person can have a speech disorder with intact language (they know exactly what they want to say but cannot say it clearly) or a language disorder with intact speech mechanics. The distinction matters for AT selection. (BoK p. 15)

Organic vs. functional speech disorders

Organic speech disorders

Organic speech sound disorders have an identifiable physical cause — neurological, structural, or sensory.

Apraxia of speech is a motor planning disorder. The person knows what they want to say and has functional muscles, but the brain cannot reliably sequence the movements needed. Speech is effortful, inconsistent, and often characterized by “groping” attempts to find the right motor sequence. (BoK p. 15)

Dysarthria results from weakness, paralysis, or poor coordination of the muscles of speech — the lips, tongue, jaw, soft palate, and breathing system. It may occur after stroke, traumatic brain injury, or in conditions like cerebral palsy or Parkinson’s disease. Speech may be slurred, slow, or hypernasally produced. (BoK p. 15)

Functional speech disorders

Functional speech disorders (articulation and phonological disorders) have no clear organic cause but affect accurate sound production.

• Articulation disorders involve errors on specific sounds: a person may consistently substitute /w/ for /r/, or omit final consonants.
• Phonological disorders reflect a systemic pattern error with a group of sounds. (BoK p. 16)

Mutism

Neurogenic mutism

Neurogenic mutism is the complete absence of speech due to neurological damage — stroke, traumatic brain injury, or conditions affecting the brain’s motor speech areas. The person may understand language fully (and have literacy intact) but cannot produce speech. AAC (augmentative and alternative communication) is the primary support. (BoK p. 16)

Selective mutism

Selective mutism is an anxiety-based condition — not a neurological or mechanical speech disorder. The person can produce speech normally in comfortable contexts (e.g., at home) but does not speak in specific situations (e.g., school, public places). It is most commonly identified in children and is treated with behavioral and psychological approaches rather than speech AT. (BoK p. 16)

Real-world example

A voice-activated customer service system requires clear, fluent speech for recognition. A user with dysarthria after a stroke cannot be understood by the system. A user with selective mutism will not attempt to speak to an automated system at all. Both are excluded by a voice-only interface. Adding a text-entry fallback removes both barriers.