Electropalatographic Analysis of Apraxia of Speech in a Left Hander and in a Right Hander

Abstract

Two cases with 'pure' apraxia of speech are reported. The articulatory disturbances were quite similar. One of the two cases was a left-handed male with a subcortical haemorrhage and the other a right-handed male with a cerebral infarct. The MRI and CT scans showed that the first case had a lesion that mainly involved the right precentral gyrus and its deep white matter, and that the second had a lesion mainly affecting the lower parts of the left precentral and postcentral gyri and their deep white matter. These findings and a literature review suggest that a corticosubcortical lesion of the lower part of the left precentral gyrus in most right handers and a lesion of the symmetric region in the right hemisphere in some left handers cause apraxia of speech. The omission errors for sounds articulated by the tongue and the hard palate were analysed using electropalatography, which records visually the dynamics of the palatolingual contact. The results demonstrated that there were three kinds of omission errors: true omissions (no palatolingual contact); omissions with incorrect contact (palatolingual contact for a different sound or undifferentiated sound); and omissions with correct contact (correct palatolingual contact for a target sound). The latter two types of omission error were observed for initial consonants and they were probably caused by a delay in air flow. The patients also showed a tendency to substitute one of the two consonants/t, t/for other sounds, which suggested that they had difficulty in the inhibition of tongue activity.

A Re-Evaluation of the Nature of Speech Errors in Normal and Disordered Speakers

“…The intrusive alveolar gesture here is reminiscent of the type of patterns found by Sugishita et al [1987] accompanying perceived omissions in their two apraxic speakers. They attributed these MAGs to an inability of the speakers to inhibit alveolar gestures.…”

“…Due to its non-invasive nature, the most popular technique for obtaining articulation records of disordered speakers has been electropalatography (EPG) [Washino et al, 1981;Hardcastle et al, 1985;Sugishita et al, 1987;Hardcastle and Edwards, 1992;Howard and Varley, 1995;Hardcastle and Gibbon, 1997;Southwood et al, 1997;Wood, 1997]. This technique only provides a record of articulations during which the tongue makes contact with the palate; thus, the question of anomalous movement amplitude is usually not investigated with this technique.…”

Primary face motor area as the motor representation of articulation

“…The assumption of a left-hemisphere speech motor module [1] comes from a multitude of observations that lesions in the lower motor cortex of the dominant hemisphere give rise to aphemia or severe impairment of articulation [2][3][4][5][6][7]. This module may well lie near the lower motor area because pure dysarthria, a rare manifestation of cortical stroke, is often accompanied by facial palsy [8][9][10], involving the part of primary motor cortex lying just laterally to the precentral knob (face-M1).…”

Characterizing Articulation in Apraxic Speech Using Real-Time Magnetic Resonance Imaging

“…The silent intrusion errors that surface in both repeated and nonrepeated apraxic speech are particularly interesting when considered along with results of past EPG studies that seem to suggest that apraxic speakers experience difficulty suppressing lingual activity, thus giving rise to errors involving substitution of /t/ and /tʃ/ for other sounds (Sugishita et al, 1987). These data, combined with our findings using rtMRI, raise the question of whether the observed "substitution" errors may, in fact, be gestural intrusion errors involving coproduction of a tongue tip gesture and another gesture not able to be captured using EPG (e.g., a labial or dorsal gesture).…”

“…This can be understood as the system slipping into the intrinsically more simple, stable frequency-locking pattern of 1:1 such that each of the /t/ and /k/ gestures occur once for every coda /p/ gesture produced (Goldstein, Pouplier, Chen, Saltzman, & Byrd, 2007;Saltzman & Munhall, 1989). Prior studies using EPG provide indirect evidence that the frequency of these gestural intrusion errors or "misdirected articulatory gestures" is higher in apraxic speech than in typical speech (Edwards & Miller, 1989;Pouplier & Hardcastle, 2005;Sugishita et al, 1987;Washino, Kasai, Uchida, & Takeda, 1981).…”