It is part of the astronomer's "personal equation." Proceeding with this "simple-reaction" experiment as a basis, the psychologists have varied the instructions to the subject so as to secure from him the different times which he takes for more complicated mental processes, such as distinguishing between two or more impressions, counting, multiplying, dividing, etc., before reacting; or they have him wait for an associated idea to come up before giving his response, with many other variations.

By comparing these different times among themselves, interesting results are reached concerning the mental processes involved and also about the differences of different individuals in the simpler operations of their daily lives.

The following research carried out by Mr.B.[4] serves to illustrate both of these assertions.
[Footnote 4: The writer.] Mr.B.wished to inquire further into a fact found out by several persons by this method: the fact that there is an important difference in the length of a person's reaction time according to the direction of his attention during the experiment.

If, for example, Mr.X.be tested, it is possible that he may prefer to attend strictly to the signal, letting his finger push the key without direct care and supervision.

If this be true, and we then interfere with his way of proceeding, by telling him that he must attend to his finger, and allow the signal to take care of itself, we find that he has great difficulty in doing so, grows embarrassed, and his reaction time becomes very irregular and much longer.