Syllable frequency and syllable structure in the spontaneous speech production of patients with apraxia of speech

Abstract

Background: The sublexical factors syllable frequency and syllable structure are known to influence error rates in patients with apraxia of speech (e.g., Aichert & Ziegler, 2004; Romani & Galluzzi, 2005). To our knowledge, these factors have almost exclusively been examined by single‐word production paradigms. However, performance on single‐word tasks is not necessarily a good predictor of spontaneous speech production, since the generation of conversational speech involves specific conditions and additional demands. This might influence the weights of syllable frequency and syllable structure in explanations of the accuracy of speech production in apraxic speakers.

Aims: Our aim was to determine if the spontaneous speech production of patients with apraxia of speech (AOS) is influenced by the factors syllable frequency and syllable structure. The two research questions that guided our investigation were: (1) Are the distribution properties of syllables in spontaneous speech different in patients with AOS compared to unimpaired speakers? (2) Do the factors syllable frequency and syllable structure affect articulatory accuracy in the spontaneous speech of patients with AOS?

Methods & Procedures: Three patients with AOS and 15 neurologically unimpaired control persons produced samples of spontaneous speech with a minimum of 1000 syllables each. Structure and frequency counts were made on the basis of the German CELEX database.

Outcomes & Results: The distribution properties of the spontaneous speech samples were similar in the apraxic speakers and the unimpaired controls. In all three patients the proportion of errors was significantly higher on low‐ than on high‐frequency syllables. In two patients a significant effect even persisted when any confound with syllable structure was ruled out. Syllable structure effects were only found within the low‐frequency syllables.

Conclusions: Syllable frequency and syllable structure play a decisive role with respect to articulatory accuracy in the spontaneous speech production of patients with AOS.

The first author of this study was supported by a grant from the DFG ‐ German research council (ZI 469/10‐2). We would also like to thank the ReHa‐Hilfe e.V. for their support. We are grateful to our colleagues from the Neuropsychological Clinic, Munich‐Bogenhausen Hospital, Munich, and to the staff from the speech therapy departments at the Rehabilitation Hospitals Bad Heilbrunn and Bad Aibling for their collaboration on clinical issues. We would also like to express our gratitude to all participants.

Keywords:

• Spontaneous speech production
• Apraxia of speech
• Syllable frequency
• Syllable structure.

Notes

The first author of this study was supported by a grant from the DFG ‐ German research council (ZI 469/10‐2). We would also like to thank the ReHa‐Hilfe e.V. for their support. We are grateful to our colleagues from the Neuropsychological Clinic, Munich‐Bogenhausen Hospital, Munich, and to the staff from the speech therapy departments at the Rehabilitation Hospitals Bad Heilbrunn and Bad Aibling for their collaboration on clinical issues. We would also like to express our gratitude to all participants.

1. Some authors ascribed these errors to a concomitant aphasic‐phonological impairment (e.g., Itoh & Sasanuma, 1984; McNeill, Pratt, & Fossett, 2004), but the observation of anticipatory as well as of perseveratory and transposition errors also coincides with many common descriptions of AOS (e.g., Dabul, 2000; Darley et al., 1975; La Pointe & Johns, 1975; Wertz, La Pointe, & Rosenbek, 1984).