Bauhaus-Universität Weimar

Fluctuations of Attention and After-images. 
235 
which has momentarily disappeared from the visual field, will bring 
it back immediately. We cannot suppose that the physiological 
rhythms are, in this case, suspended or suddenly changed. Nor have 
we any proof that quick voluntary closing of the eyes, which, as 
Münsterberg has shown, prevents fluctuation, must have this effect 
by interfering with the rhythmic reinforcement of the nerve cells 
rather than by affecting the peripheral conditions. 
In other words, the most convincing argument for the central 
origin of these fluctuations leaves, so far as further explanation is 
concerned, two possibilities. First, we may say that the conditions 
in the peripheral organ and in the afferent paths remain, duiing the 
entire series of fluctuations, unchanged, or so slightly changed that 
their respective functions continue. The stimulus is then transmitted 
steadily to the centre, e. g. to the cortical cells. Here, for a given 
interval, it produces its effect and appears in consciousness, hut, in 
the next interval, owing to the reduced activity of the centre, the 
incoming stimulus is blocked or its effect is so minimized that it is 
not perceived. Second, we may say that changes take place simul¬ 
taneously in the peripheral organ and in the brain, in such a way 
that the fluctuations are at once central and peripheral. This much 
was stated in my former article on the subject. ' The statement was 
vague; but, at the time, the evidence did not justify a more definite 
statement. It was, however, in accord with a view which has gained 
favor among physiologists, namely, that the distinction between peri¬ 
pheral functions and central functions should not be carried to extremes. 
If, instead of speaking of retinal changes as opposed to central 
changes, we should speak of changes in the cerebro-retinal mechanism, 
and employ a corresponding terminology for the other centro-sensory 
connections, we should probably be led to make greater allowance 
for the structural and functional differences in the several organs of 
sense. In the experiments which have so far been published, sufficient 
consideration has not been shown for the differences that present 
themselves as soon as we look into details. What this neglect implies 
will appear from a comparison between experiments on visual sensations 
and experiments on auditory sensations. For the most part, and 
even in the latest investigations, Masson’s disk and the ticking 
watch have been used by all observers. How far they differ is easily
        

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