Do environmental and hereditary factors affect the psychophysiology and left-right shift in left-handers?

The principal objective of this study was to investigate the reality of sinistrality in left-handed subjects. The subjects were assessed by a 20-item questionnaire with two groups taken from Oldfield's and Yetkin questionnaires. The relation of different effects on left-hand preference was studied in men and women considering familial information and writing hand. The degree of hand preference was determined by Geshwind scores (GSs). The GS degrees of hand preferences were divided into weak and strong left-hand ranging from -20% to -100%. After assessing the GSs we asked the subjects to answer 22 questions with different aims, which were especially written for only left-handers. Some of them were based on familial sinistrality and hereditary relation to left-handers. The others concerned hand, foot, eye, shoulder, and ear preferences; the psychology of left-handedness; the knowledge concerned with left-handedness; the success, ability, and interest education and skill, and morphological differences in hand and foot sizes. In the present study, it was found that the subjects have had at least one left-handed person in their family or among their relatives. Some subjects had shifted their left hand preference in favor of their right hands. Nevertheless, the left-handers have been found as a presence with their own peculiarities.