The term developmental dysphasia refers to children who fail to develop speech and language at the normal time and in the normal manner although they do not have a primary emotional disturbance nor a physical handicap, and are not globally mentally retarded or deaf. Empirical investigations of the disorder have studied auditory perception, visual perception, linguistic and articulatory function, attention and orientation, scholastic performance and reading ability, and hemispheric specialization. With the exception of the studies of auditory perception and hemispheric specialization little promising data have been generated. Investigators of auditory perception have suggested that the language disorder in developmental dysphasia may be attributable to an impairment in auditory perceptual processing. Data from studies of the hemispheric specialization of development dysphasics suggest that dysphasics may have aberrant hemispheric specialization.
Neuropsychological investigations of adult language disturbance, i.e. adult aphasia, have concluded that the left hemisphere is specialized for certain kinds of motor function, speech and language being one such function, and that it is an impairment in certain kinds of motor function which is crucial to speech and language disturbances, and not an impairment in linguistic processing or symbolic function as has been suggested by many researchers.
This research studied developmental dysphasia with the hypothesis that since this disorder involves speech and language difficulties perhaps it might be related to a deficit in certain aspects of motor functioning, specifically, the organization and execution of fine (as contrasted with gross) actions. This motor performance was also considered within the context of hemispheric specialization since: i) previous work has indicated atypical patterns of hemispheric specialization in developmental dysphasics, ii) motor functions appear to he lateralized and iii) the motor tasks lend themselves to being performed by each hand separately.
Ten developmental dysphasics were selected according to strict criteria and were administered seven measures of motor ability, several of these being nonstandardized tests designed specifically for this research. Five of these were lateralized tests (i.e., it was required that the task be performed by each hand separately), while the remaining two were nonlateralized measures. The lateralized measures were a repetitive tapping task, the Annett peg moving task, a children's sequence box task, a hand posture imitation task and a hand movement imitation task. The Illinois Test of Psycholinguistic Abilities manual expression test and an oral movement imitation task were the non-lateralized measures. It was found that the dysphasics performed more poorly than their matched control subjects on the hand posture imitation task, the hand movement imitation task and the ITPA manual expression test. On the repetitive tapping, Annett peg moving, children's sequence box and oral movement imitation tasks the dysphasics performed as well as their control subjects: A laterality effect was not observed on any of these measures for either the normal subjects or the dysphasics.
These results were interpreted to mean that developmental dysphasics have a deficit in certain aspects of manual motor function. It is proposed that this is a specific and higher order deficit, not observed in all types of motor function. Moreover, it is suggested that it is a deficit in the initiation, organization and execution of motor behavior and not in the perception. Given that a laterality effect was not observed for any of the measures, no definitive conclusions were possible regarding the hemispheric specialization of developmental dysphasics.
Data from linguistic measures administered in addition to those used for subject selection, further confirmed the receptive language deficit in the developmental dysphasics and also indicated difficuIties in the processing of written language. These latter data were interpreted to mean that developmental dysphasia may represent a language disorder which encompasses all forms of language behavior, not just oral language reception and production.