A review of directionality trends in the horizontal dimension as a function of innate and environmental factors.

This report reviews research on directionality trends in the horizontal dimension. The literature reviewed shows that such trends are predominantly a function of handedness and acquired reading-writing habits and that innate directional tendencies of left-handers are more influenced by acquired habits than those of right-handers. It is suggested that these trends may reflect some aspect of lateralization of cerebral function and that in mature adults the mixed-dominance left-handers are more influenced by environmental factors than are right-handers. Suggestions for future research include utilization of larger samples of left-handers and employment of longitudinal studies which systematically vary handedness and reading and writing habits. It is also suggested that controls for lateral dominance should be established. In addition it is suggested that reading and writing habits can be broken down into component parts and that their influence on directionality should be examined.