Apraxia of speech as a disruption of word-level schemata: Some durational evidence

This study is a preliminary test of the predictions of a dual-route speech encoding hypothesis. This hypothesis suggests that there are two routes to speech: one involves retrieval of stored word forms (direct route) and a second involves assembly of speech from subsyllabic units (indirect route) (Levelt & Wheeldon, 1994). Direct route encoding is likely to be limited to words that occur frequently and is reflected in more rapidly produced and more cohesive speech tokens. An extension of the theory suggests that apraxia of speech (AOS) might be usefully reconceptualized as an impairment of direct route speech encoding (Whiteside & Varley, 1998). Three groups of participants (normal and brain-damaged controls and AOS patients) repeated phonetically matched high/low frequency word pairs and response latency, utterance and word durations were measured. The results from response latency and word duration measures indicated preliminary support for the predictions of the dual-route hypothesis.