Dkckmbku 4, 11103.] 



SCIENCE. 



T2r> 



the areas nru concorned, but results of eliuioal 

 observations made it appear probable that the 

 «-enter for nuisele sense is there localized. 



7'/if Appliculion of the Concept of Variability 



in Jieact ion-Time Work: Dr. Robert 



Yerkes, Harvard University. 



InasnuK'h as tlie degree of constancy of re- 

 nction-tinu's differs for different species, in- 

 dividuals, conditions of the individual, modes 

 and intensities of stimulation, it is clear that 

 variability is an important quantity in the 

 analysis of reactions, which should make pos- 

 sible the qiuintitative estimation of the in- 

 fluence of the various factors which play a 

 part in determining the time of reaction. 



The mean or average variability is generally 

 determined in recent studies of reaction-time, 

 but of far more importance for comparative 

 work is what may be known as the relative 

 variability. This quantity is an index of 

 variability, which gives not the absolute vari- 

 ableness of the reaction-time, but the ratio of 

 the variability to the time of reaction. For 

 reaction-times, which are symmetrically dis- 

 tributed about a mode, the relative variability 

 may be gotten from the formula 



mean variability X 100 

 mean 



In case of asymmetrical distribution Pearson's 

 formula for obtaining the coefficient of vari- 

 ability should be used. 



Examination of reaction-time statistics in 

 which the variability is given indicates that 

 the relative variability, as well as the time of 

 reaction and the mean variability, decreases 

 with increase in the strength of the stimulus. 

 For electric stimulation this appears to be 

 true from the threshold intensity to that which 

 causes a reflex reaction, but in case of other 

 modes of stimulation it is possible that beyond 

 a certain point increase in intensity of the 

 stimulus causes slower and more variable re- 

 actions. 



Since the time of reaction varies with the 

 intensity of the stimulus it is useless to com- 

 )iare reaction-times for different modes of 

 •^tinnilation, or those of different species or 

 individuals, unless the relative variability is 

 known. Tt is not iin|irobable that careful in- 



vestigation of the relation of rt'lative variabil- 

 ity to reaction-time will furnish a satisfactory 

 basis for the accurate comparison of different 

 results. To say that one person reacts more 

 (luickly than another to a given stimulus with- 

 out taking into account the variability of the 

 reaction-time is meaningless. 



Tlie 'Specious Present' anil the Ileal Present: 



Dr. W. P. Montague, Columbia University. 



A psychosis, like all systems, possesses in its 

 totality a form or structure which is distin- 

 guishable, as the perceiving subject, from its 

 individual contents, as perceived objects. 

 Changes in the individual contents produce 

 concomitant, though generally lesser, changes 

 in the totality. The segment of duration or 

 change perceived at any one moment is not 

 itself a real change, but simply the ratio of 

 tJie change-rate of the individual contents to 

 the change-rate of the totality, at that moment; 

 and this ratio, though finite and variable, does 

 not itself require a finite time for its realiza- 

 tion. Each \inextended moment of ' real ' 

 time is thu.s adequate for the appreciation of 

 an extended period of perceptual or ' specious ' 

 time. 

 The Effects of Practice on Ihe Poggendorff 



Illusion : Mr. E. II. Cameron and Mr. W. M. 



Steele, Yale University. 



This paper reported the results of a series 

 of experiments dealing with the effect of prac- 

 tice on the Poggendorff illusion. (1) Quantita- 

 tive determinations were made with a number 

 of illusions ; (2) practice with one illusion was 

 carried on for an extended period ; (3) deter- 

 minations were again made with all of the 

 illusions which were used before the practice 

 series. 



The apparatus used was demonstrated. The 

 results show that the illusion tends to disap- 

 pear after a period of seven weeks' practice. 

 The effects of such practice were found to hold 

 good for figures other than that with which the 

 practice was made. 

 The Zollner Figure: Dr. Ciiari.es H. Jidd, 



Yale l^^niversity. 



This i)aper reported a series of (luautitative 

 determinations of the amount of illusion in 

 the Zullner figure when the figure was rotated 



