On Constructing a Reality - Understanding Understanding: Essays on Cybernetics and Cognition - page 212

let them know they are not alone. Again, the discovery we all have to make
for ourselves is the following postulate.
The Environment as We Perceive It Is Our Invention
The burden is now upon me to support this outrageous claim. I shall
proceed by first inviting you to participate in an experiment; then I shall
report a clinical case and the results of two other experiments. After this I
will give an interpretation, and thereafter a highly compressed version of
the neurophysiological basis of these experiments and my postulate of
before. Finally, I shall attempt to suggest the significance of all that to
aesthetical and ethical considerations.
Experiments
The Blind Spot
Hold topic with right hand, close left eye, and fixate star of Figure 1 with
right eye. Move topic slowly back and forth along line of vision until at an
appropriate distance (from about 12 to 14 inches) round black spot disap-
pears. With star well focused, spot should remain invisible even if topic is
slowly moved parallel to itself in any direction.
This localized blindness is a direct consequence of the absence of photo
receptors (rods or cones) at that point of the retina, the “disk,” where all
fibers leading from the eye's light-sensitive surface converge to form the
optic nerve. Clearly, when the black spot is projected onto the disk, it cannot
be seen. Note that this localized blindness is not perceived as a dark blotch
in our visual field (seeing a dark blotch would imply “seeing”), but this
blindness is not perceived at all, that is, neither as something present, nor
as something absent: Whatever is perceived is perceived “blotchless.”
Scotoma
Well-localized occipital lesions in the brain (e.g., injuries from high-
velocity projectiles) heal relatively fast without the patient's awareness of
any perceptible loss in his vision. However, after several weeks motor dys-
function in the patient becomes apparent, for example, loss of control of
arm or leg movements of one side or the other. Clinical tests, however, show
that there is nothing wrong with the motor system, but that in some cases
FIGURE 1.