What is the underlying impairment in acquired apraxia of speech?

Acquired apraxia of speech (AOS) is traditionally viewed as a disorder of s peech programming that results from loss or failure to access segmental mov ement plans, and/or the subsequent assembly of segments to form cohesive sy llables. However, more recent psycholinguistic research has proposed that s peech control systems are capable of establishing movement plans for freque ntly used syllables and words. Dual-route theories suggest that movement ge stalts are stored for high-frequency words, whereas low-frequency tokens ar e assembled afresh from sub-lexical components each time they are used. We review the implications of a dual-route model of speech control for output models of lexical processing and for the conceptualisation and management o f AOS.