blends (st, gr, bl, and so on). The ages at which these sounds are mastered completely are given for the average child: labials at three years, dentals and gutturals at about three and a half to four years, the f and v at about five years, the complicated tongue sounds during the sixth year, and the sibilants and blends during the early part of the seventh year. These sounds, however, are mastered much earlier by children who have been given definite training.
1. Davis E. A., The Development of Linguistic Skill in Twins, Singletons with Siblings, and Only Children from Age Five to Ten Years, Minneapolis, University of Minnesota Press, 1937. This study considers articulation, length of sentence, complexity of sentence structure, frequency, function, and length of different words used, and types of twins and resemblances between twin pairs. It shows that only children progressed continuously in language skill, and that there was linguistic retardation in twins to nine and one half years. This retardation grew less marked as the children grew older, and was mainly concerned with articulation.
2. Ewing A., Aphasia in Children, London, Oxford University Press, 1930. This book describes a form of speech defect in young children which has causes different from the aphasia of adults. Ewing's investigations have discovered a state of partial deafness in "aphasic" children. Part I is concerned with the investigation of hearing capacity, with a discussion of many hearing tests and the relation of hearing to speech development. Part II is an investigation of aphasic symptoms, discussing the literature of aphasia, and the speech and language development of aphasic patients.
3. Fröschels E., Psychological Elements in Speech, Section II on "Infant Speech," Boston, Expression Co., 1932. A discussion of the development of infant speech, pointing out analogies in the development of infant speech and in disorders of speech. The disorders of speech mentioned in this connection are aphasia, articulatory disorders, initial stuttering, and development-stuttering.
4. Gesell A., The Psychology of Early Growth IncludingNorms of Infant Behavior and a Method of Genetic Analysis