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Page:Popular Science Monthly Volume 44.djvu/625

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THE ORIGIN OF RIGHT-HANDEDNESS.

no preference for either hand in reaching straight before her within easy reaching distance (ten inches); but she was right-handed to a marked degree during the same period as regards movements which required effort or strain, such as grasping for objects twelve to fifteen inches distant. The left hand was used in only five cases as against seventy-four cases of the use of the right hand; and further, all these five cases were twelve-inch distances, the left hand being used absolutely not at all in the forty-five cases at longer distances.

In order to test this point further, I varied the point of exposure of the stimulus to the right or left, aiming thus to attract the hand on one side or the other, and thus to determine whether the growth of such a preference was limited to experiences of convenience in reaching to adjacent local objects, etc. The result appears in Table IV:

Table IV.
12 inches. 13 inches. 14 inches. 15 inches. Hand used.
Deviations from median line— Right. Left.
2 to 6 inches to left 10 cases 15 cases 4 cases . . . . 35 . . . .
2 to 6 inches to right 2 " 3 " 1 " . . . .
Same conditions with color stimulus . . . . . . . . . . . . . . . . 15 2

This table shows that deviation to the left in front of the body only called out the right hand to greater exertion, while the left hand fell into still greater disuse. This seems to show that dextrality is not derived from the experience of the individual in using either hand predominantly for reaching within the readiest range of that hand.

Proceeding upon the clew thus obtained—i. e., that a stronger effort brought a preferential hand reaction—a clew which seems to suggest that the hand preference is a function of the relative strength of the influence of the eye stimulus, I introduced hand observations into a series of experiments on the same child's perception of the different colors which I was making at that time, thinking that the color stimulus which represented the strongest inducement to the child to reach, might have the same effect in determining the use of the right hand as the increased distance in the experiments already described. This inference is proved to be correct by the results given in Table V:

Table V.
Color stimulus,
10 to 15 inches
Hand Right. Left. Both. May 23d to June 19th.
Number of cases 86 2 ..

It should be added that in all cases in which both hands are said to have been used, each hand was called out with evident in-