Our eyes have a natural scotoma or “blind spot” where we can’t actually take in visual information because of a lack of photoreceptive cells in the area where your optic nerve connects to your retina, the tissue that collects the information that gets processed by your brain after being transferred through the optic nerve.
The interesting thing is that this blind spot is actually a necessary feature of our vision because the condition of its possibility (the thing that makes it possible) is also the same condition that makes the whole visual experience possible. So this lack or void is a necessary feature of our vision rather than a contingency. However because our visual apparatus is binocular, each eye can fill in the blind spot of the other eye. So we don’t normally experience the blind spot but it is nonetheless there, discovered through scientific investigation.
This seems to have an interesting parallel to Kant’s dual notion of the noumenon or “thing in itself” which is said to be a condition for experience but is also necessarily excluded from it, and this noumenon is said to have both an objective-external and subjective-internal character (just like how there’s a blind spot in the visual field and a lack of photoreception in the visual eye-apparatus). But rather than supporting Kant’s attempt to ground all of phenomenal existence to such a transcendental account universally applying to every possible form of experience, this parallel seems to “provincialize” this universal to the particular biological configuration of the human organism, which is itself a historically contingent species in the continuum of biotic and abiotic evolution. Kant’s transcendental account of experience may have some truth to it, but only when re-circumscribed to the confines of a contingent, particular occasion rather than a necessary and universal one — turning it from an ultimate truth to a conventional one.
Interesting how thorough investigation and analysis of features of our biological organism actually compels us to “de-anthropocenterize” our metaphysics, helping us undo centuries of philosophical hubris that considered the human condition to be the axis mundi of all experience.