Table 1.

Types, loci, and distinguishing characteristics of motor speech disorders.

MOTOR SPEECH DISORDER TYPE	Locus	Chief distinguishing auditory perceptual characteristics	Distinguishing pathophysiology
Dysarthrias	Central or peripheral nervous system	Dependent on type	Dependent on type
Flaccid*	Lower motor neuron	Breathiness; hoarseness; short phrases; audible inspiration; hypernasality; audible nasal emisison; imprecise articulation	Weakness
Spastic	Upper motor neuron (usually bilateral)	Strained-harsh voice quality; monopitch & monoloudness; slow rate	Spasticity
Ataxic	Cerebellar control circuit	Irregular articulatory breakdowns; telescoping of syllables; distorted vowels; excess & equal stress; inappropriate variation in pitch, loudness & duration	Incoordination
Hypokinetic	Basal ganglia control circuit	Reduced loudness; monopitch & monoloudness; rapid or accelerated rate; short rushes of speech; reduced stress; repeated sounds; inappropriate silences	Rigidity; bradykinesia; reduced range of motion; movement scaling problems
Hyperkinetic	Basal ganglia control circuit	Variable, dependent on locus in speech mechanism of fast-to-slow and rhythmic-to-unpredictable movements	Involuntary movements (e.g., chorea, myoclonus, tics, dystonia, tremor)
Unilateral UMN	UMN, unilateral	Harshness; hoarseness; imprecise articulation; irregular aticulatory breakdowns; slow rate	UMN weakness; ? spasticity; ? incoordination
Apraxia of speech	Left hemisphere (predominantly frontal lobe)	Distorted sound substitutions & additions; syllable segregation; increased interword intervals; slow rate; articulatory groping; reduced accuracy with increased utterance length & complexity	Disturbed planning/programming of speech movements

^*Specific auditory perceptual characteristics that characterize flaccid dysarthrias vary as a function of the specific lower motor neurons that are involved (e.g., specific cranial and spinal nerves).