Evidence of dual-route phonetic encoding from apraxia of speech: implications for phonetic encoding models

Contemporary psycholinguistic models suggest that there may be dual routes operating in phonetic encoding: a direct route which uses stored syllabic units, and an indirect route which relies on the on-line assembly of sub-syllabic units. The more computationally efficient direct route is more likely to be used for high frequency words, while the indirect route is most likely to be used for novel or low frequency words. We suggest that the acquired neurological disorder of apraxia of speech (AOS), provides a window to speech encoding mechanisms and that the disorder represents an impairment of direct route encoding mechanisms and, therefore, a reliance on indirect mechanisms. We report an investigation of the production of high and low frequency words across three subject groups: non-brain damaged control (NBDC, N=3); brain damaged control (BDC, N=3) and speakers with AOS (N=4). The results are presented and discussed within the dual-route phonetic encoding hypothesis.