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 reënforcement as
an indication of fusion.

[1] Brückner, A.: 'Die Raumschwelle bei Simultanreizung,'
_Zeitschrift für 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_ appears never much
exceeds the threshold distance. Furthermore, there being no distinct
line of demarcation between one and two, there must be many sensations