Speech Sound Disorders (Articulation and Phonology)
Speech sound disorders is an umbrella term referring to any difficulty or combination of difficulties with perception, motor production, or phonological representation of speech sounds and speech segments—including phonotactic rules governing permissible speech sound sequences in a language.
Speech sound disorders can be organic or functional in nature. Organic speech sound disorders result from an underlying motor/neurological, structural, or sensory/perceptual cause. Functional speech sound disorders are idiopathic—they have no known cause. See figure below.
Organic Speech Sound Disorders
Organic speech sound disorders include those resulting from motor/neurological disorders (e.g., childhood apraxia of speech and dysarthria), structural abnormalities (e.g., cleft lip/palate and other structural deficits or anomalies), and sensory/perceptual disorders (e.g., hearing impairment).
Functional Speech Sound Disorders
Functional speech sound disorders include those related to the motor production of speech sounds and those related to the linguistic aspects of speech production. Historically, these disorders are referred to as articulation disorders and phonological disorders, respectively. Articulation disorders focus on errors (e.g., distortions and substitutions) in production of individual speech sounds. Phonological disorders focus on predictable, rule-based errors (e.g., fronting, stopping, and final consonant deletion) that affect more than one sound. It is often difficult to cleanly differentiate between articulation and phonological disorders; therefore, many researchers and clinicians prefer to use the broader term, “speech sound disorder,” when referring to speech errors of unknown cause.