Bauhaus-Universität Weimar

In fact, the colour-sensation does persist after the paper 
is replaced by the black. The apparatus therefore 
records a time too short by the amount of lag after the 
I stimulus has been removed. The record in this case 
? gives the minimum time during which a stimulus needs 
to work in order to be noticed. We will call it the 
|)-shortest noticeable stimulus. 
The shortest noticeable stimulus depends upon the 
intensity. With lamplight of relative intensities varying 
I from i to 256 there has been found to be a regular 
relation of time to the intensity.1 For example, the 
times for blue paper thus illuminated were on one 
! occasion as follows (Fig. 16) : 
Intensity... 1 4 16 64 
Time ... 15* 100 8* 6* 
With the apparatus of Fig. 8 experiments were made 
on the shortest possible exposure of various compli¬ 
cated objects, namely, letters and words. The letters 
were placed behind the grey spot, just as the colours 
had been. The slide fell, and the observer declared he 
had not distinguished the letter or else he told what it 
was. He attempted to name the letter even when he 
had seen only a part of it. Hereby he often named it 
correctly when he had seen only a little of it, and, on 
the other hand, he often thought he had recognised a 
letter clearly which was not present at all. 
The time of exposure required for recognising letters 
depends on the size. With letters from Snellen’s opto¬ 
types the results ran as in the following table : 
1.25 0.8 
0.8? 1.4


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