B58 W. LeConte Stevens—Physiological Optics. 
one retina has its mate in the other, and when such a pair are 
estimated. ‘There are strong reasons however for doubting the 
validity of this theory of corresponding retinal points. 
we can affirm is that experience, acquired individually and 
probably with exceeding rapidity in consequence of inherited 
tendencies, has taught us to interpret retinal sensations that are 
slightly different in the two eyes, as the signs of an external 
object possessing three dimensions in space, when the images 
are made upon parts of the concave surfaces that bear to each 
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