DISCRIMINATION AND COMPARISON C)27 



place of the touch or the sjDark. It did so infallibly, and 

 sensibly instantly ; whilst both place and movement seemed 

 to be perceived only a moment later, in memory. These ex- 

 periments were undertaken for the express purpose of ascer- 

 taining whether the movement at the sight of the spark was 

 discharged immediately by the visual perception, or whether 

 a ' motor-idea ' had to intervene between the perception of 

 the spark and the reaction.* The first thing that was mani- 

 fest to introspection was that no perception or idea of any 

 sort preceded the reaction. It jumped of itself, whenever 

 the signal came ; and perception was retrospective. We 

 must suppose, then, that the state of eager expectancy of a 

 certain definite range of possible discharges, innervates a 

 whole set of paths in advance, so that when a particular 

 sensation comes it is drafted into its appropriate motor 

 outlet too quickly for the perceptive j^rocess to be aroused. 

 In the experiments I describe, the conditions were most 

 favorable for rapidity, for the connection between the 

 signals and their movements might almost be called in- 

 nate. It is instinctive to move the hand towards a thing 

 seen or a skin-spot touched. But where the movement is 

 conventionally attached to the signal, there would be more 

 chance for delay, and the amount of practice would then 

 determine the speed. This is well shown in Tischer's re- 

 sults, quoted on p. 524, where the most practised observer, 

 Tischer himself, reacted in one eighth of the time needed 

 by one of the others. t But what all investigators have 

 aimed to determine in these experiments is the minimum 

 time. I trust I have said enough to convince the student 

 that this minimum time by no means measures what we 

 consciously know as discrimination. It only measures 

 something which, under the experimental conditions, leads 



* If so, the reactions upon the spark would have to be slower than 

 those upon the touch. The investigation was abandoned because it was 

 found impossible to narrow down the difference between the conditions of 

 the sight-series and those of the touch-series, to nothing more than the 

 possible presence in the latter of the intervening motor-idea. Other dis- 

 parities could not be excluded. 



f Tischer gives figures from quite unpractised individuals, which I have 

 not quoted. The discrimination-time of one of them is 23 times longer than 

 Tischer's own ! (Psychol. Studien, i 527.) 



