208 



SCIENCE. 



[N. S. Vol. V. No. 110. 



zero — the vanishing point — while a purely 

 qualitative change leads neither to or from 

 the zero point of sensations. Theories of 

 intensity of sensations may be classed in 

 general under two heads : (a) that the 

 stronger sensation is the weaker sensation 

 plus more of the same sensation — following 

 an analogy from the physical world which 

 may prove dangerous, and exposing psy- 

 chology to the troublesome presupposition 

 that our psychic elements (sensations) are 

 compounds; (6) that the intensity series is 

 merely a qualitative series, but ordered in a 

 series towards or from zero by the presence 

 of a second series of sensations, e.g., bright- 

 ness sensations or muscular sensations. It 

 would seem much more satisfactory to dis- 

 cover in the nature of the psycho-physical 

 process itself that which shall give to sensa- 

 tions the characteristic of an intensity 

 series. Accordingly this hypothesis is of- 

 fered : Any sensation of a given quality 

 and intensity that may arise depends upon 

 a certain physiological condition which is 

 reached only after passing successively 

 through a series of other physiological con- 

 ditions, each of which is but differing in 

 degree from zero to the given sensation. 

 That is, any sensation depends upon the 

 physiological basis which contains, in a 

 temporal series, the bases of all the weaker 

 sensations of this particular quality. The 

 final neural condition, after passing through 

 all the intermediate steps, may be called the 

 ' maximum effect ' of the stimulus. By a 

 study of the intensity of sensations pro- 

 duced by a stimulus of a known intensity 

 acting for a time less than that necessary 

 to produce its maximum effect, it is found 

 that this intensity is exactly proportional 

 to the duration of the stimulation. Con- 

 cerning the nature of the psycho-physical 

 process, nothing is postulated save that the 

 basis of the stronger sensation contains that 

 of the weaker in the time series as stated 

 above. 



3. Report of Experiments on the Reduction of 

 the Tactual Double-Point Threshold by Prac- 

 tice and on the ' Vexirfehler .' By G. A. 

 Tawney, of Beloit University. 

 The first object of the experiments was 

 to examine the view of Volkmann and Fech- 

 ner that, by daily practicing some one spot 

 of skin in the perception of two points, the 

 threshold for this perception is reduced, 

 not only for the spot actually practiced, but 

 also for the symmetrically opposite spot on 

 the other side of the body. A number of 

 threshold determinations were made on dif- 

 ferent parts of the body varying in number 

 from six to thirty-two for each subject. 

 One of these spots was chosen for special 

 practice, which continued for a period vary- 

 ing from two weeks to a month. At the 

 end of this time the threshold determina- 

 tions on the six to thirty-two different parts 

 of the body were repeated in order to com- 

 pare them with those made at the begin- 

 ning of the practice series. The instrujnent 

 used was a simple pair of compasses. The 

 results show unmistakably that where any 

 reduction of the threshold occurs as a re- 

 sult of practice it occurs over the entire 

 surface of the body; it demands, therefore, 

 a central explanation. The paper further 

 discussed the nature of the ' Vexirfehler ' 

 (double-point illusion). It was assumed 

 that the double-point illusion is the result 

 of suggestion and it was sought to free a 

 subject whose threshold formerly could not 

 be determined from the suggestion involved. 

 The experiments seemed to show that the 

 reduction of the threshold by practice is, 

 to a great extent at least, a result of sug- 

 gestion. Several series were carried out 

 for the purpose of studying the psychosis 

 underlying the 'Vexirfehler.' The results 

 seem to show that this illusion is mainly 

 due to auto-suggestion, although physio- 

 logical factors may play a subordinate part. 



4. Comparison of the Times of Simple Reactions 



