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Handedness and manual exploration

(from the chapter) Since human beings have two hands which do not interact in the same way with the environment, the emergence and evolution of manual skill in children has always been a controversial topic in philosophers, anatomists, biologists and psychologists for centuries. The question as to why the great majority of humans (between 85% and 95%) show a right-handed preference in numerous activities, such as writing, drawing, teeth brushing, etc. and, conversely, a left-handed preference in perceptive activities, remains a polemical subject today. One of the main reasons for this is that the emergence of manual skill was examined as an epiphenomenona linked to language acquisition, and not really studied as a behavior in its own right. Yet the question is important because behavioral asymmetries are regarded as a reflection of the asymmetries in the working of the two hemispheres. The left hemisphere works in a more analytical, sequential, serial and focal way and uses this skill to handle verbal data. The right hemisphere works in a more global, simultaneous, parallel and holistic way and is thus better adapted to the handling of spatial data. If we are interested in hemispherical specialization in haptic activities, and if we want to know when it emerges, we must direct ourselves towards the study of the fine perceptive/motor performances of the hand, and not towards those mobilizing the global arm-hand motor system. (PsycINFO Database Record (c) 2005 APA, all rights reserved)