Unless You Are an Octopus, You Have Blind Spots

Our eyes are amazing things, but it is our brains that are truly miraculous. The mind — our conscious experience — arises from our brains.^{1, 2} Thus understanding our brains is pretty important, because our conscious experience is everything. It is all we have. Yet in truth we do not have a conscious experience; we are our conscious experience. You are your mind, and your brain is not a reality receiver or interpreter; it is a reality generator.

Consider vision, our most dominant sense. Our conscious experience is flooded with visual stimuli. Yet contrary to our intuition, our sharp eyes do not deliver a seamless, high-definition, full-color world to our brains. Rather, our brains construct a seamless, high-definition, full-color visual experience from the weak electrochemical signals that result from photons of light striking the cells of our retinas. What we see is correlated to those signals, but our visual experience goes far beyond the raw sensory input.

Our retina is not like the image sensor in your phone’s camera, with identical pixels spread uniformly over its surface. Our retinas have densely packed, color-sensitive cells in just a small area called the fovea (6 o’clock in the diagram below). Only the fovea delivers a high-definition color signal to the brain. The rest is a blurry monochrome (although it is highlysensitive to motion). In one spot in each eye your optic nerve passes through your retina, where it spreads out and connects from the front side to the individual retinal neurons.³ In the region where the optic nerve passes through the retina there are no photosensitive cells at all. In that location in each eye, you are entirely blind.

Soerfm, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

The point at which the optic nerve passes through the retina is called the physiological blind spot or punctum caecum(literally “blind point” in Latin). If you are reading this, you have probably already found this simple experiment for finding your physiological blind spots.

Yet experience tells us that something is not quite right. Assuming you have healthy eyes, you are not blind at the punctum caecum or at any point in your visual field. If we are to be precise, what we should really say is that at the blind point, there is zero sensory input. You are not blind, but what you see in that location cannot possibly be coming from your eyes. And in fact it does not. Your vision at the blind point, and at every point comes from your brain. Your brain takes the limited, mostly monochrome, mostly blurry, partly missing visual signals from your eyes and uses it to generate our vivid, continuous visual world.

The fact that it is our brains and not our eyes that generate our visual experience explains how we have highly visual dreams at night with our eyes closed. It also explains how we handle visual saccades, French for “jerks” (as in rapid movement, not the obnoxious guy in the next cubicle). Saccades are the constant, very rapid, jerky eye movements we make all the time without knowing it. When you look at an object, your eyes do not remain fixed and motionless on that object. Instead they jump around, even as you keep your attention on one spot, yet you obviously do not experience this. Your brain filters out the movement meaning, again, that when your eye is actually in motion, mid-saccade, you cannot possibly be “seeing” the raw signal coming from your retina. Stare at yourself in a mirror. You will never catch your eyes moving. Your brain won’t let you.

Our visual systems are truly incredible, but make no mistake, your brain is generating your visual experience. Your brain is generating your experience, period, not just your vision. This has profound implications for how we understand ourselves, how we interact with the world, and with each other.

Executive coaching, assessments, and much of the work we do is about helping people find their blind spots. Our brains take care of the visual ones automatically, others require a little more work.

Nerdy notes (required to understand the title of this piece):

1. At least it appears that the mind arises from the brain. There are many good reasons to believe that it does, but technically we can’t prove it, and even assuming it does, we have no idea how or why. Although I do not believe it to be the case, you cannot prove that you are not in The Matrix.
2. Technically it is probably more accurate to say that our minds arise from our entire nervous system, not just our brains.
3. I’m an engineer and this is clearly a design flaw. Why on earth would you pass the optic nerve through a hole in the retina and connect to all those retinal cells from the front, creating a blind spot? Why not just connect them all from the back, leaving an uninterrupted retinal disc and no blind spot? Interestingly, that is exactly how it works for some animals. All vertebrates have a blind spot, but cephalopods do not. Octopi do not have blind spots. Unless you are an octopus (or other cephalopod), you have blind spots. So why are we stuck with what seems to be a clearly inferior arrangement? As Andrew Huberman likes to say, I don’t know; I wasn’t consulted in the design phase!

Caerbannog svg version, based on Jerry Crimson Mann png version., CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Note that in the octopus eye the nerve fibers lay behind the retinal neurons, meaning the optic nerve does not pass through the retinal disc, eliminating the vertebrate blind spot.

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