Page:Popular Science Monthly Volume 11.djvu/590

572 the signal was to be given with the right hand, for a white light with the left hand. In this case the mental action of deciding these alternatives and coördinating the corresponding act of volition required no less than .154, or nearly one-seventh of a second.

Other experiments have been made with the sense of sight, where the patient was instructed to give the signal by pronouncing the name of a vowel which was shown to him. If he had to distinguish between two vowels, the psychical time was prolonged .166 of a second beyond what it would have been for one vowel. If he was required to name one out of five, the prolongation was increased to .170 of a second.

Similar experiments with the sense of hearing, where the vowel was spoken to the patient and repeated by him, gave similar results. Where two vowels were selected from the mind occupied .056, and where five were used .086 of a second longer than if only one expected vowel were spoken.

Where two colors were shown, and the signal was given by a movement of the hand, or by the voice, the physiological time for the movement of the hand was found to be always greater than for the voice.

When the signal was the pronouncing of a vowel, as "i," the time required was less than when the patient was obliged to speak the vowel with a consonant before it, as "pi," or "ki," or "ti." The letter "p" was found to retard the patient .011 of a second, "t" twice as long, or .022 of a second, and "k" .021 of a second. A further result of these curious investigations was that the patient required three times as long to distinguish between two letters which were shown upon a screen as to distinguish between the two corresponding vowels when spoken.

In all these investigations the psychical time is made up of two periods: the first required by the mind to perceive the sensation or to distinguish the alternative, the second required for the mental act of willing the signal. An attempt has been made to measure each of these. The experiment for this purpose was so arranged that the patient was to hear several vowels, but was directed to give the signal only upon hearing a certain one of them. Under this arrangement the patient concentrated his attention upon the perception of the vowel at hearing which he was to act. He prepared himself, as far as could be, to pronounce it the moment he heard it. Before he heard it he willed to speak it on the instant that he should perceive it. There remained only the act of recognizing the vowel when it should be spoken, of distinguishing it among the other vowels. The act of volition was in this way eliminated from the physiological time, and the simplest mental act of distinguishing was calculated from the result. This result, based upon this and similar experiments, was that the mental act of distinguishing required about one twenty-third of a second of time. The whole psychical time being about one-twelfth