Error Prediction in Acquired Apraxia of Speech
Marquardt, Thomas P., Schneider, Holly G., Jacks, Adam, Journal of Medical Speech - Language Pathology
Six participants with acquired apraxia of speech predicted whether or not they would produce correctly 180 words that varied from one to three or more syllables in length and from low to high abstractness. Participants predicted they would produce very few errors (6.3%), but produced a much higher number (27%). Accuracy of predicted errors also was very low, with only two participants correctly predicting more than 10% of their errors. Error analysis revealed that participants consistently produced more errors as a function of both increasing syllable length and word abstractness. However, a contrasting pattern was found in the error prediction results. Participants predicted more errors as a function of increased word abstractness, but not as a function of word length. Results suggest, that speakers with apraxia have limited knowledge of motor complexity factors, such as word length, that affect speech production.
Keywords: apraxia of speech; speech sound errors; motor complexity; word abstractness
Apraxia of speech (AOS) results from damage to neural circuits of the frontal lobe that are responsible for programming speech movements. AOS is characterized by inefficient translation of intact phonological representations into spatiotemporal parameters of articulatory movements (McNeil, Robin, & Schmidt, 2008). Speech production in AOS is marked by articulatory distortions, lengthened speech segment and intersegment durations, and prosodic abnormality (Wambaugh, Duffy, McNeil, Robin, & Rogers, 2006).
Speech errors in apraxia are affected by motor complexity, with increased numbers of errors expected on longer compared to shorter words and on consonant clusters compared to singleton consonants (e.g., Duffy, 2005; Johns & Darley, 1970; Wertz, LaPointe, & Rosenbek, 1984). The ability of speakers with apraxia to predict errors as a function of motor and linguistic factors, however, has received very limited research interest. Deal and Darley (1972) investigated the ability of 12 participants with AOS to predict speech errors. They found a significant correlation between prediction and production of words. However, two of the participants could not predict any errors, three were able to predict less than 50% of their errors, and four produced 50% more errors than they predicted. Impaired prediction of errors in speakers with AOS suggests that damage to the neural circuitry encoding motor programs for speech affects not only production of speech movements but also judgments related to them.
The purpose of this study was to investigate the ability of speakers with apraxia to predict speech errors as a function of word length and word abstractness.
Six adults with apraxia of speech and mild Broca's aphasia secondary to left frontal brain damage participated in the study (Table 1). Included were three males and three females at least six months post onset of brain damage. The diagnosis of apraxia of speech with mild Broca's aphasia was based on the administration of a standard aphasia battery (e.g., Boston Diagnostic Aphasia Examination, 2nd Edition, Goodglass & Kaplan, 1983) and a motor speech examination. The participants demonstrated impaired prosody, dysfluent verbal expression, inconsistent segmental errors and minimal auditory comprehension deficits. The diagnosis of apraxia of speech was confirmed by two speech-language pathologists based on review of the clinical evaluation results and observation of the participant in conversation.
TABLE 1. Participant Demographic Data. Participant Gender Age Etiology Post-Onset Lesion Site (Years) 1 F 59 CVA 4 Left parietal 2 F 70 CVA 5 Left basal ganglia 3 M 43 Gunshot 22 Left frontal/temp. 4 M 45 CVA 3 Left frontal 5 F 53 CVA 12 Left frontal 6 M 64 CVA 6 Left basal ganglia/thalamus
A total of 180 nouns varying from one to five syllables in length were used as stimuli for the study. …