THE MEASUREMENT OF PERSEVERATION AND ITS 

 VALUE AS AN INDEX OF MENTAL CHARACTER. 



By JOHN GKAV. 



No science makes much progress until its \'otaries 

 succeed in applying to its phenomena the methods 

 of exact measurement. The sciences of chemistry 

 and physics, after the introduction of exact methods 

 of weighing and of measuring space, temperature and 

 potential, advanced by leaps and bounds, ^^'e have 

 good reason, therefore, to believe that the application 

 of measurement would lead to a corresponding great 

 advance in that science, by no means the least import- 

 ant, which deals with the evolution of man himself. 



It will be convenient, in explaining the nature of 

 the exact science of man, or, as it is usually called, 

 anthropometry, to regard man as a machine, com- 

 prising a framework or structure and highh' complex 

 functions. 



To measure the framework of man is a compara- 

 tively easy matter. With the graduated rod and 

 the callipers u e can measure statures, head diameters. 

 and other dimensions of the body : and the weight 

 can be measureef with the weighing machine. 



The simpler physiological functions, such as 

 acuity of vision, colour vision, and other sensory 

 characters can also be readily measured. I'nit when 

 we come to deal with the more complex physiological 

 functions, those usuall\' known as psychological, the 

 difficulty greatly increases. 



The value of measurements of ps\'chological or 

 mental characters is, however, so great that strenuous 

 efforts have recently been made by anthropologists 

 to discover some more or less exact methods. 

 Intelligence, for example, pla^-s so important a part 

 in all the affairs of human life, that a fairly accurate 

 method of measuring it would be of the greatest 

 practical value to the educationist, to the military or 

 naval officer, and to the business man, not to speak of 

 the impulse which it would give to the science of man. 



Most of the methods of measuring intelligence at 

 present in vogue are personal estimates by teachers 

 or others who are acquainted by long experience 

 with the mental character of the person to be tested. 

 These methods have been found to be only very 

 rough approximations, as there is by no means good 

 agreement between the results obtained by different 

 observers. 



The examination test is recognised as a good test 

 of intelligence, but it involves other factors which 

 have little or nothing to do with intelligence, and its 

 correlation with success in after life is not very high. 



It appears to me that simple and exact methods 

 of measuring certain physiological properties of the 

 brain which have a great influence on our mental 

 growth, promise to give much more valuable results 

 in the measurement of mental character than either 

 the personal estimate or the examination test. 



As an example of this I take the measurement of 



the persistence of a nervous current or disturbance 

 in the brain after the external impulse has ceased. 



For this purpose I have devised a simple apparatus 

 b\- which flashes of coloured light can be thrown in 

 rapid succession into the e\e (see Figure 1). 



The apparatus consists of a revolving mirror, the 

 axis of which is horizontal, and which can be turned 

 at an\- required speed by a handle and belt gearing. 

 The speed at which the axis is rotating at any 

 instant is show n hv a speed indicator connected to 

 its free end. 



The mirror re\'ol\es in a dark box ha\ing windows 

 of coloured glass directh' above and below the 

 mirror. Outside each window is a screen of white 

 paper fixed at an angle of 45° to the plane of the 

 glass, and illuminated by an electric glow lamp, or 

 by other constant source of light. 



A beam of tliffuse light thus passes through the 

 coloured glass of the window and impinges on the 

 mirror. .\s the mirror revolves, the coloured reflected 

 beam passes over an aperture in the side of the box, 

 against which the eve of the person being tested is 

 placed. When the reflected beam has passed over 

 the aperture, the colour impulse on the retina ceases 

 until the mirror has reached the position in which 

 it reflects the next coloured beam of light into the eye. 



The experiments of Shelford Bidwell. and of 

 others, have shown that the sensation of a colour 

 persists for a short time after the external impulse 

 has ceased. If the duration of this persistence is 

 equal to the time interval between two successi\e 

 impulses from the revolving mirror, the colour will 

 appear to be continuous. But if the persistence is less 

 than the time interval, the colour will appear to flicker. 



In order to measure the duration of the persistence 

 in an\- given person all that is necessary is to 

 ascertain from the speed indicator on the axis of the 

 mirror, the exact number of revolutions which the 

 axis is making when the flicker disappears. It is best 

 to start very slowly, and gradually increase the 

 number of revolutions of the mirror until the flicker 

 disappears. The reading is taken from the speed 

 indicator at this critical speed. The persistence of 

 colour sensations in the person being tested is 

 inversely proportional to the critical speed. 



In order that observations made on difterent 

 persons, and at different times, may be comparable, 

 the illumination should be kept constant. Any 

 \-ariation in the luminosity of the coloured light will 

 change the critical speed. 



A different persistence will, as a rule, be found with 

 difterent colours. It is desirable that the persistence 

 should be measured with each of the three primary 

 colours separately. 



Experiments made by Nichols, Ferry, Abney, 



500 



