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 state of fatigue, a short conversation will bring a certain relief and relaxation, and the words which the speaker hears in reply will produce a general stimulation of psychical energy for the moment.  Moreover, the mere existence of the social conversational intercourse will raise the general emotional mood, and this feeling of social pleasure may be the source from which may spring new psychophysical powers.  Nevertheless the fundamental fact, after all, is that any talking during the labor, so far as it is not necessary for the work itself, surely involves a distraction of attention.  Here, too, the individual is not conscious of the effect.  He feels certain that he can perform his task just as well, and even the piece-worker, who is anxious to earn as much as possible, is convinced that he does not retard himself by conversation.