Page:American Journal of Psychology Volume 21.djvu/242

 with the three above mentioned nurses. As examinations of this kind can be rendered into a foreign tongue only with the greatest difficulty, I will content myself with presenting the general results, and with giving some examples. I first undertook the experiment with the friend of the head nurse, and judging by the circumstances she appeared only slightly moved. The head nurse was next examined; she showed marked excitement, her pulse being 120 per minute immediately after the experiment. The last to be examined was the nurse who attended to the cleaning of the room in which the theft occurred. She was the most tranquil of the three; she displayed but little embarrassment, and only in the course of the experiment did it occur to her that she was suspected of stealing, a fact which manifestly disturbed her towards the end of the experiment.

The general impression from the examination spoke strongly against the head nurse. It seemed to me that she evinced a very “suspicious,” or I might almost say, “impudent” countenance. With the definite idea of finding in her the guilty one I set about adding up the results.

One can make use of many special methods of computing, but they are not all equally good and equally exact. (One must always resort to calculation, as appearances are enormously deceptive.) The method which is most to be recommended is that of the probable average of the reaction time. It shows at a glance the difficulties which the person in the experiment had to overcome in the reaction.

The technique of this calculation is very simple. The probable average is the middle number of the various reaction times arranged in a series. The reaction times are, for example, placed in the following manner: 5,5,5,7,7,7,7, 8,9,9,9, 12, 13, 14. The number found in the middle (8) is the probable average of this series. Following the order of the experiment, I shall denote the friend of the head nurse by the letter A, the head nurse by B, and the third nurse by C.

The probable averages of the reaction are:

No conclusions can be drawn from this result. But the average reaction times calculated separately for the indifferent reactions, for the critical, and for those immediately following the critical (post-critical) are more interesting.

From this example we see that whereas A has the shortest reaction time for the indifferent reactions, she shows in