Page:Mind (Old Series) Volume 9.djvu/116

 104 G. STANLEY HALL AND E. M. HABTWELL. was generally most conspicuously the case if the movement was made mainly from the shoulder, but was usually also the law for movements made at the elbow, wrist, and knuckles. One per- son seemed, from these movements, right-sided at the shoulder and elbow, and left-handed at wrist and knuckles. The ratio of the excess-distance of the preferred hand to the whole excur- sion varied greatly with different persons, and somewhat, though much less, with the same person at different sittings. Between twenty and fifty centimetres from the central pin the asymmetry of movement was greatest, and was less for both greater or less excursions, as if the median plane and the position of fully extended arms were the bases from which intermediate positions were estimated. Weighting each hand alternately had no con- stant effect, but if, instead of slipping the finger-tips directly upon the ruler-edge, they rested upon and moved slides, and one of these was made to move with greater resistance than the other, the amplitude of movement was reduced. In one single series of observations, when the sitter was unusually fatigued at night, the non-preferred hand constantly made the greater excursions, and on another occasion of fatigue the same person made an extra- ordinary excess of movement with the preferred hand. Neither of these results, however, could be obtained again by strongly fatiguing one arm just before the sitting. In all these cases the movements were made with one sudden impulse of hmervation, as nearly equal right and left as possible. If the impulses be more slowly sustained, or corrected at their close, to give fuller play to afferent impressions, unilateral excess is slightly less. II. If these movements, instead of being simultaneous, be successive, with intervals of one and of four seconds between, there is a tendency to reduce the excess of the preferred hand, and, in some individuals, to make an equal or even greater error in favour of the non-preferred hand, i.e., for a left-handed person, whose left-hand goes farthest in simultaneous movements in- tended to be equal, to now make the greater excursion with the right hand, and vice versa for a right-handed person. The degree of right- or left-handedness seems, however, to be involved. The right and left hand preceded alternately in these observa- tions, but our figures show as yet no constant difference, due to the precedence of either hand. III. If, with both eyes open, the experimenter stick a pin into, or move one fixed to a slide upon the ruler to, a certain point, and then, with careful ocular measurement, attempt to place the other pin an equal distance on the other side of the middle point, there is still a pretty constant, though much smaller, excess on the side of the preferred hand. This indicates that, to binocular vision, a line at right angles to the median plane seems a little longer to the left than to the right of it, if the observer is right- handed an error in the same sense as that of the hand in simul- taneous movements. One case was found, however, in which the