Bauhaus-Universität Weimar

A Comparison of Sight and Touch [From the Journal of Physiology, Vol. III, No. 3, Offprint]
Bowditch, H. P.
should be here remarked that the relative positions in the scale of accuracy 
assigned to the methods of indirect vision and of touch with the same' 
hand have been determined by averaging all the observations in all the 
series, and that if the comparison is made between the same series in 
different sets, very varying results will be obtained, according to the 
series selected. 
Moreover, the differences between these methods, as expressed in the 
column of general averages, are small in amount. 
It is therefore probable that an increased number of observations 
might lead to some modification of the conclusions above formulated. It 
seems, however, to be sufficiently well established, that of the methods 
here employed for determining the position of objects around us, that 
of direct vision gives the lest results, that of touch with the opposite hand 
the worst, and that the other methods occupy intermediate positions. 
It seems also evident that fixation of the head, as above described, 
diminishes the accuracy with which objects around us can be localized. 
Effects of Time.—A comparison of the results obtained in the 
different series of observations shows that in the 1st, 2nd, 3rd, and 4th 
sets the smallest errors were obtained in the 2", in the 5th and 6th sets 
in the 0", and in the 7th set in the 4" series. The average errors in 
all the observations of a given series, irrespective of the sets to which 
they belong, are given in the lowest line of Table VIII. 
From these figures it would seem that when an observer having 
determined the position of an object, either by sight or touch, waits two 
seconds with closed eyes before making a movement in its direction, the 
average error will be a little less than when he makes the movement as 
soon as he has determined the position of the object. In other words, it 
seems that when a mental image of position in space has been formed, its 
accuracy and definiteness increase for a brief interval, and then gradually 
In order to investigate this phenomenon a little more accurately, 
two other sets of experiments with direct vision were undertaken, each 
consisting of five series of 100 experiments each, in which the interval 
was 0,1, 2, 3,4 seconds respectively. These experiments differed from 
those heretofore described in the fact that the object used was a card on 
which concentric circles, 5 mm. apart, were drawn, as shown in the 
accompanying figure, PI. XVII. A black spot 5 mm. in diameter in 
the centre served as the point on which the eyes were fixed, and toward 
which the movement of the hand was directed. A needle set in a handle 
was used instead of a pencil, and the distance from the central point of


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