The data on the occurrence of left-handedness among children who stammer or whose development of speech is retarded, d iffer a great deal in the existing literature. Some authors find a strikingly high number of left-handers suffering from defects of speech, while others give substantially lower figures, thus failing to confirm or even denying the etiological significance o f left-handedness.
The author’s own findings concern children of pre-school age, whose type of dexterity was examined with regard to the genotype. Out of 356 stammering children 46 per cent were right-handed, and the rest, that is 54 per cent, were left-handed (including also those who were able to use both hands equally well; the latter accounted for 13.02 per cent). 75 children altogether were examined for retarded development of speech (excluding those who were mentally deficient or hard of hearing). Only 34.3 per cent of them were definitely right-handed, whereas 65.7 per cent were left-handers (partly also using both hands with equal dexterity — 11.4 per cent). In nearly all these cases the left-handers were retrained in the use of their right hands.
As a result of his own findings the. author regards other types of dexterity than downright right-handedness as one of the possible causes giving rise to the defects of speech. Suppression or even re-training of the natural type of dexterity interferes with the process of the formation and stabilization of the cortical areas for speech, reading and writing.