right half of the brain, causes in man
impairment in the upper right-hand quadrant of both retinae: destruction
of the lower lip of the fissure causes impairment in the lower
right-hand quadrants. Destruction of the calcarine region of one
hemisphere produces therefore "crossed hemianopia," that is, loss of the
opposite half of the field of vision. But in this hemianopia the region
of central vision is always spared. That is, the piece of visual field
which corresponds with the yellow spot of the retina is not affected in
either eye, unless the calcarine regions of both hemispheres are
destroyed. This central point of vision is connected therefore not with
one side of the brain only but with both.

The impairment of sight is more severe in men than in lower animals.
Where the destruction of the visuo-sensory cortex in one calcarine
region is complete, a candle-flame offered in the hemianopic field
cannot even be perceived. It may hardly excite a reflex contraction of
the pupil. In such cases the visual defect amounts to blindness. But
this is a greater defect than is found in the dog even after entire
removal of both occipital lobes. The dog still avoids obstacles as it
walks. Its defect is rather, as said above, a complete loss of interest
in the visual images of things. But a dog or monkey after loss of the
visual cortex hesitates more and avoids obstacles less well in a
familiar place than it does when entirely blind from loss of the
peripheral organ of vision. In man extensive destruction of the visual
cortex has as one of its symptoms loss of memory of localities, thus, of
the paths of a garden, of the position of furniture, and of accustomed
objects in the patient's own room. This loss of memory of position does
not extend to spatial relations ordinarily appreciated by touch, such as
parts of the patient's own person or clothing. There is nothing like
this in the symptoms following blindness by loss of the eye itself.
Those who lose their sight by disease of the retina retain good memorial
pictures of positions and directions appreciated primarily by vision.

Cases of disease are on record in which loss of visual memory has
occurred without hemianopia. Visual hallucinations referred to the
hemianopic side have been observed. This suggests that the function of
visual memory in regard to certain kinds of percepts must belong to
localities of cortex different from those pertaining to other visual
percepts. The area