Bauhaus-Universität Weimar

Measurements of Illusions and Hallucinations in Normal Life
Seashore, C. E.
G. JE. Seashore, 
3. Visual memory of size causes a less intense illusion of weight 
than that which is produced by looking at the blocks while lifting* 
4. Size has no influence on the perception of weight when the 
observer has no knowledge of it. 
fourth series of experiments : Dependence of the illusion of weight 
upon the senses by which knowledge of size is acquired. 
In all the foregoing experiments the perception of difference in 
size was purely visual. The next problem was to settle the question : 
Does the illusion of weight vary with the different senses by which 
the image of size is produced ? 
It is impossible to draw a strict line of demarcation between the 
different sensory elements which, besides sight, unite in building up 
a percept of size, because they generally cooperate, and their effects 
fuse. For the purpose of comparison, I aimed to get a measure of 
the illusion of weight due to size when knowledge of size was 
acquired through each of the following channels predominatingly : 
(1) muscle sense, (2) touch, (3) sight, (4) muscle sense, touch and 
These conditions were approximately attained by the following 
respective methods of procedure. 
1. Without having seen the blocks, the observer seated himself on 
a high stool behind a screen, in such a position as was occupied when 
he stood by the tray and looked at the apparatus, so that his arm and 
hand would be comfortably adjusted over, the tray, on the other side 
of the screen. The blocks were then handed him in the same order 
as before, but placed on end on the tray, so that by dropping his 
thumb and fingers around a block the observer included it in his 
grasp, holding it by the circumference ; he thus acquired a knowl¬ 
edge of its size mainly by the muscle sense in the fingers. 
2. Seated in the same position, after a brief rest, the observer held 
out his hand, not resting it on anything, and the blocks were placed 
on his flat palm, one at a time. An image of the height (length) of 
the block was inevitably transmitted from the experience in the first 
set, but the proportional size was here estimated chiefly by the 
area of touch or pressure. 
3. The method of estimating comparative size by direct sight, as 
pursued in the previous experiments, eliminates all other sensory 
elements than sight.


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