CRIME DETECTION.

Hauraki Plains Gazette, Volume XXXVI, Issue 4824, 18 March 1925, Page 4

CRIME DETECTION.

.— USE OF INSTRUMENTS. i .. ' RECORDING THE EMOTIONS.

(By

F. Aveling,

Ph.D., D.Sc., in the

"Daily MAIL.”) There is perhaps nothing so difficult as to estimate and appraise emotions. We can tell, generally, from his behaviour when a man is enraged, or afraid, or dejected. Artists can catch the bodily expression of the soul where mere observers see only a mask. But how are we to tell from any examination of overt behaviour or play of feature, or even invisible bodily alteration, precisely what emotionally toned thoughts are passing* through a man’s mind ? Perhaps - we cannot always ; but sometimes we certainly can ; for there are devises for measuring bodily changes that undoubtedly betray mental tension. For example: One person of two

has stolen an important document. One only—by supposition—knows Its contents, and that knowledge will inevitably be betrayed if both are put through the ordeal of a psychological examination. The method is simple.. There is no “torture.” Each is merely required to reply with the first word of which he thinks to a word read from a prepared list by the investigator. Some -of the words read are irrelevant to the d ime ; others have a direct connection with it. The person who has no knowledge of the stolen document reacts with words normally associated with those read out; his measured reactiontimes (in fractions of a second) are approximately equal; he does not persist in replying again and again witii tlie same word ("perseverating”). The other reacts with words connected with the substance of the document. He "slows down” on relevant words, or those immediately following them in the list. He reacts with the same word over and over again, or he names things—being on his guard—that he sees around him. Tlie test is a good one. But there are better tests than this which can be used, either alone or in conjunction with it. No one, who has lived .through an emotional crisis, such as a crime or other goul-stirring event, is entirely unaffected by it. Recall the events to him in any fashion, direct or indirect, and apply a pneumograph (to record changes in his breathing) or a sphygmograph (to take tracings of his. pulse beats and blood pressure). Your recorded curves will betray the stare of his mind. If your “test” is irrelevant because the testee had. not lived through tlie experience suspected, it will mean nothing to him; and ho changes will be recorded in the tracings. But if an emotional complex in the subconscious is stirred they will mercilessly register the associated physiological disturbances. THE TELL-TALE LIGHT. < But there is a more sensitive bodily indication still of the occurrence of such mental states. Electrical changes that take place in the body are known to be connected with emotions (taking this term in its broad House as including desires, aversions, and the likes). Maae your tesfee’s body the fourta ressitance in a Wheatstone bridge, placing the electrodes upon .the palm and back of his hand ; and balance the bridge by altering a valuable re-

sistance so that no current flows , through the galvanometer in circuit ■ with il. In these conditions the gal- ; vanometer mirorr hangs isteady, and the spot of light deflected from it does not show notable deflections, j But now apply the test, suggesting I thoughts closely related to the susl pected .experience, and note the move- • mentis of the tell-tale light. ! When by such means the .emotions • are stirred there is a fall in the elec- • trical resistance of the hand, the balance of tlie bridge is upset, current J passe's through the galvanometer, 1 and tlie mirror swings its ray of light J along the scale, thus registering the - emotional disturbance involved. J It would, of course, be dangerous 1 to use such tests, and to draw eonclu--1 sions from their results, without making use of principles of interpreta- ’ tion which cannot be discustsed here. 1 But with caution the psychologist, bearing in mind the possible sources r . of error, chn draw his conclusions ’ rightly enough; for he looks upon ,j the data he obtains from his tests as diagnostic, in the same way as a B physician reads the symptoms of his a patient.