There have been various experimental studies made to determine how much divergences in the mental activity of different races are determined by differences in racial inheritance. Such experiments have been conducted chiefly upon very simple traits and capacities. The accuracy of sensory response among different races has, for example, been examined. There have proved to be, in regard to these, slight differences in the effectiveness and accuracy of response. There are racial differences in hearing, as tested by the ticking of a watch or clock artificially made. In this test, Papuans, to take an instance, were inferior to Europeans. The sense of touch has been similarly tested, and comparatively negligible differences have been found. In regard to the five senses, their efficiency seems to be about equal in all the races of mankind. The proverbial keenness of vision of the Indian, for example, is found to be due to a superior training in its use, a training made imperative by the conditions of Indian life. In reaction time tests--that is, tests in the speed of simple mental and motor performances--the time consumed in response has been found to be about the same for all races tested. The results have been similar with regard to certain simple processes of judgment or inference: There are a number of illusions and constant errors of judgment which are well known in the psychological laboratory, and which seem to depend, not on peculiarities of the sense organs, but on quirks and twists in the process of judgment. A few of these have been made the matter of comparative tests, with the result that peoples of widely different cultures are subject to the same errors, and in about the same degree. There is an illusion which occurs when an object, which looks heavier than it is, is lifted by the hand; it then feels, not only lighter than it looks, but even lighter than it really is. The contrast between the look and the feel of the thing plays havoc with the judgment. Women are, on the average, more subject to this illusion than men. The amount of this illusion has been measured in several peoples, and found to be, with one or two exceptions, about the same in all. Certain visual illusions, in which the apparent length or direction of a line is greatly altered by the neighborhood of other lines, have similarly been found present in all races tested, and to about the same degree. As far as they go, these results tend to show that simple sorts of judgment, being subject to the same disturbances, proceed in the same manner among various peoples; so that the similarity of the races in mental processes extends at least one step beyond sensation.[1] [Footnote 1: Woodworth: "Racial Differences in Mental Traits," _Science_, New Series, vol. 31, pp. 179-81.] Professor Woodworth also points out that these simple tests are not adequate to measure general intelligence.