208 E. B. TITCHENER— ETHNOLOGICAL TESTS OF SENSATION. 



that distance at which two points can be distinctly felt, but . . . that 

 distance at which they yield a sensation perceptibly different from 

 that yielded by a single point." It has long been known, however, 

 that between the limits "point" and "two points" there are a num- 

 ber of distinguishable perceptive forms. Gates, working recently 

 in my laboratory, distinguished " circle," " line " and " dumb-bell " ; 

 but there were slight differences within these categories ; and there 

 is no doubt that more such forms could be made out.*^ Suppose, 

 then, that an observer is set or disposed for " dumb-bell " ; his limen 

 will be relatively high. Suppose, on the other hand, that he is set 

 for " circle " ; his limen will be relatively low. In either event he 

 will be reporting " a sensation perceptibly different from that yielded 

 by a single point " and lying on the hither side of " two points dis- 

 tinctly felt"; but the limens wall be the limens of two different per- 

 ceptive forms, and therefore will not be comparable the one with the 

 other. Here, I take it, is the principal key to the wide range of 

 McDougall's results. Some of his observers judged "two" as soon 

 as the impression of the points differed in the slightest degree from 

 "one"; others judged "two" only when the points were on the 

 brink of falling apart or had actually done so. If this inference is 

 correct, the comparison of the Alurray Islanders with the English- 

 men is null and void. 



I made, to test it, a rather venturesome experiment. With IMc- 

 Dougall's instrument " it was not possible satisfactorily to apply the 

 two points at an interval less than 2 mm."' The aesthesiometers 

 regularly used in my laboratory have hard-rubber points (diameter 

 I mm.) which may be directly apposed. With our instruments, 

 therefore, it is possible to employ a dual stimulation with a separa- 

 tion of o mm. ; in other words it is possible to compare the impres- 

 sion of a single point with that of two apposed points. It occurred 

 to me that I might be able, under the suggestive influences of 

 McDougall's method, to discriminate these two impressions. I asked 



6 E. J. Gates, " The Determination of the Limens of Single and Dual Im- 

 pression by the Method of Constant Stimuli," Amer. Journ. Psych., XXVI., 

 1915, 152 ff. M. Foucault ("LTllusion paradoxale et le seuil de Weber," 

 1910, 124 f.) distinguishes six intermediate perceptive forms. 



7R, 191. 



