Consider this...

"I can live with doubt, and uncertainty, and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Richard Feynman

At the end of the last exciting episode, we left off just as signals were racing up the optic nerves from the retina, en route for the brain!

The optic nerves arrive at a thingie (technical term…) called the thalamus, in the middle of the lower part of the brain, right at the top of the brain stem. The thalamus receives sense data from various organs and relays it out to different parts of the brain for handling, like a dispatcher. It sends optical data to a whole set of places at the back of the brain in a region called, logically enough, the visual cortex.

Lovers of detail will note that the image from the retina, like that from a camera lens, is upside down and flipped left-to-right. This is corrected by the visual system so that we “see” things in “the mind’s eye” as being right-side-up. Also, you probably have heard that the left side of the brain in some way “handles” the right side of the body and vice versa. So you might think that the left brain controls the right eye and the other way around, but that is not how it works at all. In fact, all the visual information, what we see, from the left side of each eye goes to the right brain, while date from the right side of each eye goes to the left brain. (The cortex, the big creepy-wormy-looking part of the brain, is in two parts connected by a bunch of nerve fibres called the corpus callosum, sort of a cable. Cut the CC and you get someone with a real split personality.) So if the optical part of, say, the left brain is damaged, we may see things only on the left side of our field of vision, but with both eyes. Strange, huh?

Meanwhile, back in the visual cortex, the nerve signals arrive at a whole slough of different regions. One region is specialized in handling color, another shape, another movement, and so on. Damage to one of these areas results, e.g., in someone who sees everything in black-and-white, or who sees a sequence of still images rather than movement. Finally, the results of all these analyses are merged together to create the complete (complete as possible) image.

So there we have it. Electromagnetic radiation (light) may be emitted by an object (for instance, if it is heated) or different frequencies (colors) may be reflected or scattered by an object, depending on the composition and surface of the object. The rays (particle-waves) from this process traverse the lenses of the eye and are focused on detectors deep in the retina. The detectors transform some of the light energy into electrical signals which are sent up the optic nerve to the thalamus, which relays them to the visual cortex at the back of the brain. Different parts of the cortex analyze the signals to search for color, shape, movement and so on. The results are then merged and form the “image” we see in our “mind’s eye”. Simple, n’est-ce pas?

We really do “see” in our brain. And what we see is not exactly what is out there, as it is filtered by our own sensors and reconstructed in specific ways by our brains.

The other senses, hearing, feeling, taste and smell, work in similar ways, being analyzed by other parts of the brain.

This explains perhaps not how, but at least where our image of the world in front of us is put together and shown to us — and how it is not necessarily what is.

Whew!