Left-Handedness

LEFT-HANDEDNESS, a subject who prefers to use the left hand in their various actions. It is customary to distinguish between forced and congenital forms of left-handedness. Forced left-handedness is caused by an invalid state of the right hand, which has occurred following irreparable damage to this hand (in industry, in war, etc.) with symptoms of right-sided traumatic brachial plexitis, ankylosing arthritis, etc. Forced left-handedness is also encountered in cases of paralysis of the right hand that has developed after suffering acute poliomyelitis, after complete or partial amputation of the right hand, etc. Congenital left-handedness among students of labor schools in the city of Moscow (based on material of 6,192 children), according to Kapustin, occurs in 1% of cases; according to Griesbach, among the German population, left-handedness is observed in 1.15% of cases. The study of the physical development of left-handers shows that various structural anomalies, for example, cranial deformities, strabismus, etc., are found in 34% of children versus 14.8% of right-handed children (Kapustin); according to Stier, various degenerative signs in left-handers occur twice as often as in right-handers. It has also been noted that severe speech disorders are observed significantly more often in left-handers than in right-handers; according to Schafer, severe speech disorders occur in 2.3% of left-handers versus 0.7% in right-handers; among stutterers, left-handers are found, according to Kapustin, in 3% of cases; it has been established that left-handed children often learn to speak very late and with difficulty. It is known that left-handers are found in large numbers among the mentally deficient; thus, Ganter found 45.8% left-handers among 155 mentally deficient individuals; a large percentage of left-handers is observed among epileptics: according to Steiner—in 19.3% of cases, according to Ganter—45.9%. Some researchers (Gordon, Ziehen, and others) find a close connection between left-handedness and not only stuttering but also congenital strabismus, seeing their common cause in a congenital innervational anomaly of the nervous system, similar to congenital asymmetry of facial innervation, etc. In one-third of cases, left-handedness occurs as a familial trait; however, the recessive heredity of left-handedness has not yet been fully studied. The greatest difficulty is the certain challenge of distinguishing genotypically determined left-handedness from paratypical left-handedness, as well as the fact that the degree of left-handedness varies greatly in individual cases. Many researchers, for example, Griesbach, Luddeckens, and others, attribute the origin of left-handedness to the congenital functional superiority of the right hemisphere of the brain, caused by its better blood supply; according to Weigandt, left-handedness can be a consequence of an inversion of the central nervous system (situs viscerum inversus). The motor center of speech and the center of writing in left-handers are located in the right hemisphere; motor aphasia in left-handers is usually combined with left-sided hemiplegia. In addition to questioning and dynamometry, the 'mirror writing' test, which, according to Schafer, occurs in 42% of left-handers, can help in identifying left-handedness. Left-handers, while using their left hand for performing ordinary daily needs, often use their right hand for writing. Regarding ambidexterity, there is a unanimous opinion in the medical literature that the practical implementation of such training is not advisable, because by developing both centers simultaneously, one can cause inhibition of the more powerful center located in the left hemisphere; this point of view is held by Schafer, Griesbach, Stier, Luddeckens, Kapustin, and others. The experience of forced training of the left hand in right-handers in German and Belgian schools was not crowned with success. According to observations by Gordon, Froeschels, and others, the attempt to accustom left-handers to constantly use their right hand often entails the appearance of stuttering or strabismus, which, however, ceases upon abandoning the attempt to force the training of the right hand in left-handers.