The Principles of Psychology, Volume 1 (of 2)James, William
Philosophy
The Principles of Psychology, Volume 1 (of 2)
James, William
Psychology
of my inward images of sight, but of my sight altogether.[28] Recent
pathological annals seem to offer a few such cases.[29] Meanwhile there
are a number of cases of mental blindness, especially for written
language, coupled with hemianopsia, usually of the rightward field of
view. These are all explicable by the breaking down, through disease,
of the _connecting tracts_ between the occipital lobes and other parts
of the brain, especially those which go to the centres for speech in
the frontal and temporal regions of the left hemisphere. They are to
be classed among disturbances of _conduction_ or of _association_;
and nowhere can I find any fact which should force us to believe that
optical images need[30] be lost in mental blindness, or that the
cerebral centres for such images are locally distinct from those for
direct sensations from the eyes.[31]
Where an object fails to be recognized by sight, it often happens
that the patient will recognize and name it as soon as he touches it
with his hand. This shows in an interesting way how numerous the
associative paths are which all end by running out of the brain through
the channel of speech. The hand-path is open, though the eye-path be
closed. When mental blindness is most complete, neither sight, touch,
nor sound avails to steer the patient, and a sort of dementia which
has been called _asymbolia_ or _apraxia_ is the result. The commonest
articles are not understood. The patient will put his breeches on one
shoulder and his hat upon the other, will bite into the soap and lay
his shoes on the table, or take his food into his hand and throw it
down again, not knowing what to do with it, etc. Such disorder can only
come from extensive brain-injury.[32]
The _method of degeneration_ corroborates the other evidence localizing
the tracts of vision. In young animals one gets secondary degeneration
of the occipital regions from destroying an eyeball, and, _vice versâ_,
degeneration of the optic nerves from destroying the occipital regions.
The corpora geniculata, thalami, and subcortical fibres leading to the
occipital lobes are also found atrophied in these cases. The phenomena
are not uniform, but are indisputable;[33] so that, taking all lines of
evidence together, the special connection of vision with the occipital
lobes is perfectly made out. It should be added, that the occipital
lobes have frequently been found shrunken in cases of inveterate
blindness in man.
_Hearing._
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