Size-weight illusion among the blind.
35
succession the objects to be judged, and dropping them, if small, from
one hand to the other, or by weighing them upon the tips of the fingers,
as in the case of coins. In the methods of these experiments he had no
previous experience.
O was also fully aware of the illusion. He, like M, considered the
third series of judgments the least satisfactory, and expressed the same
preference for grasping rather than mere lifting upon the palm. O
thought that size was less diverting in the first series than in the second.
Experiments.
(1) The first series of tests was that in which the knowledge of size
was gained through the muscle sense, corresponding to Seashore’s
“ fourth series, H, muscle sense.” An A and a B block, resting on end
upon a soft pad, were lifted in succession, being grasped around the
circumference by the thumb and middle finger of the right hand. If the
weights were judged unequal, the B was replaced by another of the same
set. Because the observer did not have to make any choice of B’s, but
to consider only two blocks at a time (selected by the one conducting
the experiment), he could fix his attention upon the question of equality
of weight undistracted by the knowledge of the number of blocks that
might possibly be compared.
( 2 ) In another set of experiments the block was laid on the palm of