Lingual kinematics and coordination in speech-disordered children exhibiting differentiated versus undifferentiated lingual gestures

Background: Electropalatographic investigations have revealed that a proportion of children with articulation/phonological disorders exhibit undifferentiated lingual gestures, whereby the whole of the tongue contacts the palate simultaneously during lingual consonant production. These undifferentiated lingual gestures have been interpreted to reflect a 'motor constraint', with the tongue tip and body incapable of operating independently. Aims: The present study aimed to provide further insight into the speech motor control abilities of children with articulation/phonological disorders by using electromagnetic articulography to track the movements (velocity, acceleration, distance, duration) of, and the coordination between, the tongue tip and tongue body during lingual consonant production. Methods & Procedures: Comparisons were made between two children with persistent articulation/phonological disorders who exhibited differentiated electropalatographic gestures (9.58 and 10 years), one child with persistent articulation/phonological disorder who demonstrated undifferentiated lingual gestures (11 years), and a group of four control children (mean age=10.98 years, standard deviation=0.48). The children were asked to read aloud single-syllable words containing word-initial /t, s, k/ consonants, with tongue tip and tongue body movements recorded using the electromagnetic articulography AG200 system (Carstens Medizinelektronik GmbH, Germany). Outcomes & Results: Kinematic analysis revealed increased kinematic values for /s/ for the two children with articulation/phonological disorders and differentiated electropalatographic gestures compared with the control group. One of these children also exhibited increased /k/ duration. Reduced acceleration was exhibited by one child with differentiated electropalatographic gestures during /t/ production, and by the child with undifferentiated lingual gestures during /k/. Regarding coordination, lag times between the tongue tip and body were variable between and within children. Spatial contribution to consonant production discriminated between the children with differentiated electropalatographic gestures and undifferentiated lingual gestures, with excessive movement of the tongue body exhibited for alveolar consonants by the child with undifferentiated lingual gestures. Conclusions: All three of the children with articulation/phonological disorders demonstrated aberrant lingual kinematics. The child who exhibited undifferentiated lingual gestures further exhibited excess tongue body movement during alveolar consonants, suggestive of poor motor control, an immature or deviant bracing system, and/or a compensatory mechanism to counteract potential disturbances in tongue tip fine motor control. Electromagnetic articulography provided a means of examining speech motor control deficits, including disturbances in tongue movement and coordination, in children with articulation/phonological disorders