PLAN OF THE INVESTIGATION. 17 



centers commonly follows enormously complex patterns. Granting all 

 the difficulties, we still believe that the principle of simplicity is an im- 

 portant practical guide in the selection of measurable phenomena, even 

 though it must remain for the present a principle of relative simplicity. 



A third principle that guided us in the selection of our techniques is 

 the principle of customary reaction. Wherever the practice curve is 

 not intentionally an object of investigation, we believed that our ex- 

 periments should be so arranged that the motor response of the subject 

 will be a thoroughly natural and familiar act. The theoretical advan- 

 tage of customary reaction is that, in view of the large number of pre- 

 experimental responses of a similar character, the relatively few ex- 

 perimental instances would not operate to introduce a practice curve in 

 the results. 1 It was on this principle that we chose adequate eye- 

 reactions instead of any arbitrary opening or closing of special reaction 

 keys. The adaptive movement of the eyes, by which a suddenly 

 appearing peripheral object is fixated, has been practiced since birth. 

 It does not have to be taught the subject for experimental purposes. 

 It consequently seemed unlikely to us that any practice effects of our 

 relatively short experimental series would materially affect the results. 

 The sequel will show that our technique did not entirely eliminate 

 unusual limitation in the variety of possible positions and consequent 

 practice. But that does not affect the value of the principle. It was on 

 similar grounds that we chose the familiar speech-reactions to visual 

 word-stimuli in place of the more unfamiliar controlled association tests. 



It should be emphasized that neither the principles of selection nor 

 the techniques for measuring the selected processes were elaborated 

 solely for the study of the effects of the ingestion of alcohol. With the 

 exception of the Martin's Faradic threshold measurements and the 

 association experiments, for which Dr. F. L. Wells was responsible, 

 both the theory and the techniques of all our measurements have been 

 elaborated by Dodge 2 through a number of years with special reference 

 to their bearing on mental work and mental fatigue. Not only were 

 the technique and apparatus in general thoroughly tried out, but the 

 particular equipment of the psychological laboratory had been installed 

 and tested in the previous acidosis experiments. Furthermore, assis- 

 tants had been thoroughly trained to this investigation before the alco- 

 hol problem was begun. 



*Bryan and Harter, Psychol. Review, 1S97, 4, p. 27; also 1899, 6, p. 346; Book, The Psychology 

 of Skill, 1908; Swift, Mind in the Making, New York, 1908. 



"Detailed references to the original papers are given in the bibliography of the various processes. 



