In the quiet of the vision therapy room, we often treat the eye as a simple lens, focusing on clarity and muscle movement. The last few days I have been reflecting on the late Richard Masland’s seminal work, We Know It When We See It, I am reminded that the eye is less like a camera and more like a high-end laboratory.
To understand the neurobiology of vision is to understand the very architecture of human thought. As Masland points out, the line between “seeing” and “thinking” is much thinner than we ever dared to imagine.
For decades, the retina was dismissed as a “simple” neural system. Textbooks taught us it had just a few major cell types. Then came the revelation: neurobiologists discovered 29 distinct types of amacrine cells and 13 types of bipolar cells.
Why such immense complexity at the very first stage of sight? Masland provides the answer: “The world that you think you see is not the world that actually exists. It has been altered by your retina, fragmented into dozens of different signals for transmission to the brain.”
Essentially, your retina is a microprocessor, similar to the one in your smartphone but far more sophisticated. It doesn’t just pass light along; it parses the visual image into separate components. One stream of signals reports on edges, another on movement, another on color intensity. By the time information hits the optic nerve, it has been “pre-processed” into a million different data points by retinal ganglion cells—some sustained, some transient—operating through a complex dance of lateral inhibition.
One of the most profound insights Masland shares is the connection between sight and touch. He points out that the signals sent by the retinal ganglion cells function remarkably like the touch signals sent by skin sensory neurons. This provides biological weight to Maurice Merleau-Ponty’s famous philosophical claim that vision is the brain’s way of touching.
This isn’t just a metaphor. Evolutionarily and embryologically, the retina is a piece of the brain that has pushed forward to meet the world. Masland writes: “Non-scientists rarely recognize that the central nervous system includes not only the brain itself but also the spinal cord and the retina… Most of the neurons of the retina and the spinal cord are bona fide brain cells.”
These cells live behind the blood-brain barrier, they exist in a “privileged chemical environment.” This isolation is what allows for the incredible stability and high-speed processing required to keep us from walking into walls or missing a fast-moving ball.
Perhaps the most vital concept for those of us in the therapy room is Plasticity. We often think of vision as a “fixed response”—the light hits the eye, and the brain reacts. Masland flips this on its head: “Plasticity is a general rule in the brain – not just in sensory systems… In vision, the nerve nets of the brain can learn to anticipate the identity of an object in the world – to supplement the raw information coming from the retina with its knowledge of what it has seen before.”
This means that much of what we call “perception” is actually learned. Our brains are constantly guessing what comes next. Our nerve nets recognize combinations of features because they have seen them ten thousand times before.
This is why vision therapy works. We aren’t just strengthening muscles; we are leveraging this inherent plasticity. We are teaching the “nerve nets” to re-allocate resources, to better anticipate the world, and to recover from injuries that have disrupted the flow of those “separate streams” of signals.
Masland’s conjectures extend into the philosophical. He touches on the “motion after-effect” illusion (that strange sensation where the world seems to drift after you have stared at a waterfall) and the classic question of whether your perception of the color “red” matches mine.
If our retinas are microprocessors that fragment the world, and if our perception is a learned response based on our unique history, then no two people truly “see” the same world. Our visual reality is a creative act, a synthesis of raw signals and personal history.
We are not passive observers of our lives.
We are active creators of our visual reality.
Every time you focus on a page or track a bird in flight, your “bona fide brain cells” in the retina are performing a miracle of micro-computation.
As we continue to explore the “roots and ruins” of how we process our world, let’s remember that vision is a skill—a learned, plastic, and deeply personal dialogue between our inner biology and the outer world.
The next time you see something beautiful, remember: you aren’t just seeing it. You are knowing it.