The Aetiology of Idioglossia.

in 1891 to describe a defective condition of speech in two brothers aged ten-and-a-half and nine years respectively, which gave the impression of an individual language. Idioglossia may be defined as lalling or dyslalic speech which is so extreme in degree as to render it incomprehensible to the ordinary listener. A parent or one accustomed to hearing it spoken by a particular child may learn to comprehend it; but the idioglossic speech of another child will not necessarily be understood without study. Various authors have attributed this speech manifestation to: 1. a faulty perception of speech, the child merely repeating the sounds as he hears them (McReady2); 2. a faulty motor coordination of articulation due to a brain defect of the motor speech centre (Hadden3, Thomas4); 3. a faulty motor coordination of articulation secondary to defective intelligence (Wyllie5); and 4. a faulty auditory perception due to faulty development of the auditory speech centre (Kerr6, Guthrie7, Worster-Drought and Allen8). These various theories suggest that idioglossia has a varied aetiology, which will be seen to be the case on careful analysis. Recently, however, Worster-Drought and Allen have attempted to establish the thesis that idioglossia is peculiar to congenital auditory imperception (congenital word-deafness) and that those cases reported in the literature in the past fifty years which have been ascribed to other causes have been erroneously interpreted. They have attempted to discredit such aetiologic factors as motor articulatory inco-ordination and mental deficiency, assuming that the latter, for instance, was the result of deprivation rather than the exciting cause. This stand has influenced Morison9 and the Barton-Halls'0 to believe that idioglossia is characteristic of congenital auditory imperception alone. Further, it has led these writers into reporting certain cases as congenital auditory imperception which do not belong in this category. For instance, the Barton-Halls reported three cases of idioglossia as cases of congenital auditory imperception, one of which certainly was a case of motor dyslalia and another possibly due to mild mental retardation. Idioglossia is manifest in the speech of children other than those afflicted with congenital auditory imperception. It is the purpose of this paper to outline the varied aetiology of idioglossia and to show that it is merely a stage