Pebkuary 19, 1904.] 



SCIENCE. 



301 



sence of preliminary explanation or its exact 

 •nature when given has a decisive influence on 

 the character of the replies. The threshold for 

 the back of the hand lies between 1 and 2 cm., 

 and this is the same as the threshold for the 

 difference between sensations B and Cj for 

 persons who deliberately seek to make this dis- 

 tinction. Continued practise tends to intro- 

 duce Vexirfehler — to make interpreters out of 

 the simplists; and the difference between the 

 more and the less intelligent subjects, at first 

 very marked — the intelligent having a lower 

 threshold and being more subject to the Vexir- 

 fehler — tends to diminish. It is interpreta- 

 tion of the sensations, especially those of class 

 B, and not improvement in attention or a real 

 lowering of the threshold, that explains these 

 effects of practise. 



(c) The Besults of Distraction of Attention. 

 — ^Distraction may occur when attention is 

 strongly directed elsewhere, or when there is 

 difficulty in fixing the attention at all. The 

 usual method of producing it consists in 

 having the subject execute two tasks at once. 

 Wlien this is tried, the resulting mental states 

 may vary enormously in different persons: 

 there may be an easy and rapid alternation 

 of attention between the two tasks, and thus 

 no distraction; or an irregular alternation, 

 with many errors and confusions; or a fixa- 

 tion in one direction, in which case the second 

 task is suspended or becomes automatic. The 

 author had his subjects carry out long addi- 

 tions aloud, and made contacts when the effort 

 of attention to the figures, as clearly indicated 

 by the voice, was greatest. Cases where at- 

 tention alternated, going actually to the con- 

 tacts when they were made, without distrac- 

 tion, could be easily distinguished from those 

 where true distraction occurred, and presented 

 no differences from the normal results. In- 

 vestigations were made also of cases where 

 distraction occurred as a result of mental 

 revery, and on account of congenital defect in 

 backward children. The effect of distraction 

 is to produce a systematization of the replies, 

 showing itself in an automatic repetition of 

 the same reply, either ' one ' or ' two ' ; or to 

 produce replies that are due wholly to chance. 

 The former effect, systematization, probably 



characterizes distraction with fixed attention; 

 the latter is produced during distraction with 

 mobile attention, due either to exterior causes 

 or to congenital weakness. 



(d) The Interpreters. — The author had his 

 own tactile sensitivity tested, adopting two 

 mental attitudes: in the one he answered 

 ' two ' only when he was certain that he felt 

 two distinct contacts, ' one ' in all doubtful 

 cases; in the other he sought to make an in- 

 terpretation for the doubtful cases, to deter- 

 mine whether the sensations of class B were 

 occasioned by one point or two. In the latter 

 case he obtained a lower threshold and more 

 numerous errors for the single contact. One 

 of his subjects exhibited in early trials a thresh- 

 old of 1.5 cm.; a year later, one of 0.5 cm., 

 but had meanwhile become fully acquainted 

 with the processes and results of sesthesiom- 

 etry, and this fact alone accounted for the 

 difference. In general, the interpreters, who 

 form the majority of intelligent adults, and 

 thus of the subjects who have been employed 

 in researches in assthesiometry, are character- 

 ized (1) by a lower threshold for the ' double 

 sensation,' which signifies not a greater de- 

 gree of tactile acuteness, but merely a differ- 

 ence of judgment, of mental attitude; and (2) 

 by a larger nimiber of errors for the single 

 contact. There are very many types of inter- 

 preters — sceptical, deliberate, unconscious, etc. 

 — of which the author describes several. True 

 hypersBsthesia may exist, and a probable case is 

 described. It reveals itself not merely by the 

 ambiguous apparent lowering of the threshold, 

 which is usually only apparent, but also by an 

 increase in the delicacy with which the dis- 

 tance separating the two points can be esti- 

 mated for distances lying ordinarily below the 

 threshold. 



(e) Influence of Practise and Suggestion on 

 the Position of the Threshold. — Transform a 

 simplist into an interpreter, and you have an 

 apparent lowering of the threshold. The trans- 

 formation may take place spontaneously, or 

 it may be due to a suggestion, to seeing or 

 touching the apparatus, to a knowledge that 

 all the points are of equal thickness, to ob- 

 serving that two points very near together 

 give a sensation of thickness, to an expecta- 



