Developmental Risk: Evidence from Large Nonright-Handed Samples
Table 1
Influence on the lateralization process: evidence and implication.
Type of influence
Effect evidenced
Hypothesis for research
Genetic
Children with left-handed parents more often become left handers but not in adopted samples.
Becoming left-handed is as physiological as becoming right-handed. Some people do not inherit the genetic influence, therefore lateralizing themselves by the other influences or even by chance. Healthy genetic left-handed develop an original mind in comparison with right-handed individuals [31–33].
Hormonal/developmental
Greater prevalence of nonright handedness in males. Cerebral lateralization more pronounced in males.
Any brain injury before, during and after birth contradicts the lateralization process.
Results depend on global or focal brain suffering. If global, some ambidextrous subjects suffer bilateral brain damage. If focal, some 100% right-handed and some 100% left-handed suffer hemispheric dysfunction [1, 10, 28].
Neuropsychological
Each hand shows an ability advantage corresponding to the specialization of the direct linked hemisphere.
The right hand is better at communicating, and the left hand is better at visual-spatial tasks [35–37].
Learning
Children take progressively advantage of their lateralization by building body-space relationships and developing constructional abilities.
Lateralized children develop a better spatial sense than nonlateralized ones. Risks for academic learning are lower in lateralized than ambidextrous children. Target: arithmetic, eidetic reading, and writing [38, 39].
