If the only fact we had to explain was that two points are often thought to be one when they are near together, ‘fusion’ might be a good hypothesis, but we have other facts to consider.  If this one is explained by fusion, then the mistaking of one point for two must be due to diffusion of sensations.  Even that might be admissible if the Vexirfehler were the only phenomenon of this class which we met.  But it is also true that several contacts are often judged to be more than they actually are, and that hypothesis will not explain why certain arrangements of the stimulating objects are more likely to bring about that result than others.  Still more conclusive evidence against fusion, it seems to me, is found in the fact that two points, one on each hand, may be perceived as one when the hands are brought together.  Another argument against fusion is the fact that two points pressed lightly may be perceived as one, and when the pressure is increased they are perceived as two.  Strong pressures should fuse better than weak ones, and therefore fusion would imply the opposite results.  Brueckner[1] has found that two sensations, each too weak to be perceived by itself, may be perceived when the two are given simultaneously and sufficiently near together.  This reenforcement of sensations he attributes to fusion.  But we have a similar phenomenon in vision when a group of small dots is perceived, though each dot by itself is imperceptible.  No one, I think, would say this is due to fusion.  It does not seem to me that we need to regard reenforcement as an indication of fusion.

   [1] Brueckner, A.:  ‘Die Raumschwelle bei Simultanreizung,’
   Zeitschrift fuer Psychologie, 1901, Bd. 26, S. 33.

My contention is that the effects sometimes attributed to fusion and diffusion of sensations are not two different kinds of phenomena, but are identical in character and are to be explained in the same way.

Turning now to the explanation of the special experiments, we may begin with the Vexirfehler.[2] It seems to me that the Vexirfehler is a very simple phenomenon.  When a person is stimulated with two objects near together he attends first to one and then to the other and calls it two; then when he is stimulated with one object he attends to it, and expecting another one near by he hunts for it and hits upon the same one he felt before but fails to remember that it is the same one, and hence thinks it is another and says he has felt two objects.  Observers agree that the expectation of two tends to bring out the Vexirfehler.  This is quite natural.  A person who expects two and receives one immediately looks about for the other without waiting to fixate the first, and therefore when he finds it again he is less likely to recognize it and more likely to think it another point and to call it two.  Some observers[3] have found that the apparent distance of the two points when the Vexirfehler