Speech perception and motor control in children with Down syndrome

Learning by observation and learning by doing in Down and Williams syndromes

New skills may be learned by active experience (experiential learning or learning by doing) or by observation of others' experience (learning by observation). In general, learning by observation reduces the time and the attempts needed to learn complex actions and behaviors. The present research aimed to compare learning by observation and learning by doing in two clinical populations with different etiology of intellectual disability (ID), as individuals with Down syndrome (DS) and individuals with Williams syndrome (WS), with the hypothesis that specific profiles of learning may be found in each syndrome. To this end, we used a mixture of new and existing data to compare the performances of 24 individuals with DS, 24 individuals with WS and 24 typically developing children on computerized tasks of learning by observation or learning by doing. The main result was that the two groups with ID exhibited distinct patterns of learning by observation. Thus, individuals with DS were impaired in reproducing the previously observed visuo-motor sequence, while they were as efficient as TD children in the experiential learning task. On the other hand, individuals with WS benefited from the observational training while they were severely impaired in detecting the visuo-motor sequence in the experiential learning task (when presented first). The present findings reinforce the syndrome-specific hypothesis and the view of ID as a variety of conditions in which some cognitive functions are more disrupted than others because of the differences in genetic profile and brain morphology and functionality. These findings have important implications for clinicians, who should take into account the genetic etiology of ID in developing learning programs for treatment and education.

Speech impairment in Down syndrome: a review

PURPOSE

This review summarizes research on disorders of speech production in Down syndrome (DS) for the purposes of informing clinical services and guiding future research.

METHOD

Review of the literature was based on searches using MEDLINE, Google Scholar, PsycINFO, and HighWire Press, as well as consideration of reference lists in retrieved documents (including online sources). Search terms emphasized functions related to voice, articulation, phonology, prosody, fluency, and intelligibility.

CONCLUSIONS

The following conclusions pertain to four major areas of review: voice, speech sounds, fluency and prosody, and intelligibility. The first major area is voice. Although a number of studies have reported on vocal abnormalities in DS, major questions remain about the nature and frequency of the phonatory disorder. Results of perceptual and acoustic studies have been mixed, making it difficult to draw firm conclusions or even to identify sensitive measures for future study. The second major area is speech sounds. Articulatory and phonological studies show that speech patterns in DS are a combination of delayed development and errors not seen in typical development. Delayed (i.e., developmental) and disordered (i.e., nondevelopmental) patterns are evident by the age of about 3 years, although DS-related abnormalities possibly appear earlier, even in infant babbling. The third major area is fluency and prosody. Stuttering and/or cluttering occur in DS at rates of 10%-45%, compared with about 1% in the general population. Research also points to significant disturbances in prosody. The fourth major area is intelligibility. Studies consistently show marked limitations in this area, but only recently has the research gone beyond simple rating scales.

Neural mechanisms underlying action observation in adults with Down syndrome

Results of a magnetoencephalography (MEG) brain imaging study conducted to examine the cortical responses during action execution and action observation in 10 healthy adults and 8 age-matched adults with Down syndrome are reported. During execution, the motor responses were strongly lateralized on the ipsilateral rather than the contralateral side in the Down syndrome group. Observation of movement activated a network of cortical regions that was similar to the control group; however, there was no significant peak activity in the motor areas. In addition, the overall pattern of neural activation was more scattered and less organized in the Down syndrome group. These results further support the hypothesis of a dysfunction in the execution/observation matching system in adults with Down syndrome.

The use of electropalatography (EPG) in the assessment and treatment of motor speech disorders in children with Down's syndrome: evidence from two case studies

BACKGROUND

Many children experience significant difficulties in developing key aspects of speech. For some, these communication difficulties are compounded by co-occurring intellectual disabilities.

METHOD

This paper presents two case studies from a larger on-going longitudinal study of the effectiveness of using electropalatography (EPG) to address the intelligibility problems experienced by many children and young people with Down's syndrome (DS). EPG, an innovative computer-based tool for assessing and treating speech motor difficulties, enables the speaker to 'see' the placement of his or her tongue during speech and to attempt to correct any lingual palatal errors.

RESULTS

This visual supplementation of auditory feedback offers potential therapeutic benefits for children with intellectual disabilities, many of whom show relative strengths in visual vs. auditory and simultaneous vs. sequential processing. EPG also provides therapists with an objective measure of articulatory ability.

CONCLUSIONS

Findings from these two case studies demonstrate the potential utility of EPG in both the assessment and treatment of speech motor disorders in DS.

Changes in mu rhythm during action observation and execution in adults with Down syndrome: implications for action representation

The human mirror neuron system is thought to be the underlying basis of perception-action coupling involved in imitation and action understanding. In order to examine this issue we examined the recruitment of the mirror neuron system, as reflected in mu rhythm suppression in a population of adults with Down syndrome (DS) with known strengths in imitation but with impairments in perceptual-motor coupling. Ten healthy adults and 10 age-matched adults with (DS) participated in the study. Subjects were asked to make self-paced movements (execution), and view movements made by the experimenter (observation). The action consisted of reaching with the dominant hand to grasp and lift a cup. Cortical responses were recorded with a whole head magnetoencephalography (MEG) system. Both groups demonstrated significant attenuation of the mu rhythm in bilateral sensorimotor areas when executing the action. Typical adults also demonstrated significant mu suppression in bilateral sensorimotor areas during observation of the action. In contrast, when observing the movement, adults with DS showed a significantly reduced overall attenuation of mu activity with a distinct laterality in the pattern of mu suppression. These results suggest that there is a dysfunction in the execution/observation matching system in adults with DS and has implications for the functional role of the human mirror neuron system.