the facts prove is that the centers are at that time not conscious. It
would be at present an unwarrantable assumption to make, that these
centers are therefore disconnected from the retina, at the optic
thalami, the superior quadrigeminal bodies, or wheresoever. On broad
psychological grounds the action-theory of Münsterberg[25] has
proposed the hypothesis that cerebral centers fail to mediate
consciousness not merely when no stimulations are transmitted to them,
but rather when the stimulations transmitted are not able to pass
through and out. The stimulation arouses consciousness when it finds a
ready discharge. And indeed, in this particular case, while we have no
other grounds for supposing stimulations _to_ the visual centers to be
cut off, we do have other grounds for supposing that egress _from_
these cells would be impeded.

[25] Münsterberg, Hugo, 'Grundzüge der Psychologie,' Leipzig,
1900, S. 525-561.

The occipital centers which mediate sensations of color are of course
most closely associated with those other centers (probably the
parietal) which receive sensations from the eye-muscles and which,
therefore, mediate sensations which furnish space and position to the
sensations of mere color. Now it is these occipital centers, mediators
of light-sensations merely, which the experiments have shown most
specially to be anæsthetic. The discharge of such centers means
particularly the passage of excitations on to the parietal
localization-centers. There are doubtless other outlets, but these are
the chief group. The movements, for instance, which activity of these
cells produces, are first of all eye-movements, which have to be
_directly_ produced (according to our present psychophysical
conceptions) by discharges from the centers of eye-muscle sensation.