which are just about as much like one as they are like two, and hence
they must be lumped off with one or the other group. To the
mathematician one and two are far apart in the series because he has
fractions in between, but we perceive only in terms of whole numbers;
hence all sensations which might more accurately be represented by
fractions must be classed with the nearest whole number. A sensation
is due to a combination of factors. In case of the _Vexirfehler_ one
of these factors, viz., the stimulating object, is such as to suggest
one, but some of the other conditions--expectation, preceding
sensation, perhaps blood pressure, etc.--suggest two, so that the
sensation as a whole suggests _one-plus_, if we may describe it that
way, and hence the inference that the sensation was produced by two
objects.

[2] Tawney, Guy A.: 'Ueber die Wahrnehmung zweier Punkte
mittelst des Tastsinnes mit Rücksicht auf die Frage der Uebung
und die Entstehung der Vexirfehler,' _Philos. Stud._, 1897, Bd.
XIII., S. 163.

[3] See Nichols: 'Number and Space,' p. 161. Henri, V., and
Tawney, G.: _Philos. Stud._, Bd. XI., S. 400.

This, it seems to me, may account for the appearance of the
_Vexirfehler_, but why should not the subject discover his error by
studying the sensation more carefully? He cannot attend to two things
at once, nor can he attend to one thing continuously, even for a few
seconds. What we may call continuous attention is only a succession of
attentive impulses. If he could attend to the one object continuously
and at the same time hunt for the other, I see no reason why he should
not discover that there is only one. But if he can have only one