of devoting
himself to one complex function, has to carry out secondary movements
which appear to be quite easily performed and not to hinder him in his
chief task. Often his own feeling may endorse this impression. Of
course the individual differences in this direction are very great.
The faculty of carrying on at the same time various independent
functions is unequally distributed and the experiment can show this
clearly. It is also well known from practical life that some men can
easily go on dictating to a stenographer while they are affixing their
signature to several hundred circular letters, or can continue their
fluent lecture while they are performing experimental demonstrations.
With others such a side activity continually interrupts the chief
function. Then some succeed better than others in securing a certain
automatism of the accessory function to such a point that its special
acts do not come to consciousness at all. For example, I watched a
laborer who was constantly engaged in a complicated technical
performance, and he seemed to give to it his full attention.
Nevertheless he succeeded in moving a lever on an automatic machine
which stood near by whenever a certain wheel had made fifty
revolutions. During all his work he kept counting the revolutions
without being conscious of any idea of number. A system of motor
reactions had become organized which remained below the threshold of
consciousness and which produced only at the fiftieth recurrence the
conscious psychical impulse to perform the lever movement. Yet whether
the talent for such simultaneous mastery of independent functions be
greater or smaller and the demand more or less complex, in every case
the principal action must be hampered by the side issue. To be sure,
it may sometimes be economically more profitable to allow the
hindrance to the chief work in order to save the expense of an extra
man to do the side work. In most cases, however, such a consideration
is not involved; it is simply an ignoring of the psychological
situation. As the accessory work seems easy, its hindering influence
on other functions is practically overlooked. Psychological laboratory
experiments have shown in many different directions that simultaneous
independent activities always disturb and inhibit one another.

We must not forget that even the conversations of the laborers belong
in this psychophysical class. Where a continuous strain of attention
has produced a s