The salient features of AOS that have gained broad consensus for differential diagnosis (Ballard, Tourville, & Robin, 2014; Duffy, 2013; McNeil et al., 2009) include
- reduced overall speech rate;
- phoneme distortions and distorted substitutions, additions, or complications;
- syllable segregation with extended intra- and inter-segmental durations; and
- equal stress across adjacent syllables.
These features are consistent with deficits in the planning and programming of movements for speech and are noted to increase with greater syllable length and motoric complexity.
AOS can improve over time (e.g., in acute stages of stroke recovery, in response to therapy), remain stable, or worsen (e.g., primary progressive apraxia of speech).
The following other speech characteristics may not be unique to AOS and can also occur with co-existing dysarthria or aphasia.
- Consonant errors greater than vowel errors
- Voicing errors (blurred distinctions between boundaries of voiced–voiceless consonants)
- Prolonged phonemes
- Telescoping of syllables (e.g., "disaur" instead of "dinosaur")
Rate and Prosody
- Slow overall rate, regardless of accuracy of productions
- Alternative motion rates (AMRs) that may be characterized by place or manner errors
- Poorly sequenced sequential motor rates (SMRs)
- Disrupted fluency with attempts at self-correction
- Difficulty initiating articulatory sequences—may be accompanied by audible or silent groping behaviors marking false starts and restarts
- Sound and syllable repetitions
Linguistic and nonspeech/non-oromotor features that are observed during clinical presentation typically depend on the site of lesion and comorbid conditions. These include the following:
- Aphasia—language comprehension and/or production deficits
- Dysarthria—motor speech disorder characterized by impaired neuromuscular speech movements due to weakness or paralysis, spasticity, incoordination, involuntary movements, or reduced movement range
- Nonverbal oral apraxia—difficulty programming orofacial musculature for nonspeech movements
- Apraxia of swallowing—difficulty programming muscles of the head and neck for coordinated swallowing
- Limb apraxia—difficulty programming purposeful limb movements, often of both extremities
- Varying degrees of right-sided weakness and spasticity