How Vision Works
The science of how our eyes gather visual information is well documented and generally agreed upon by those studying human anatomy. As light is reflected from an object in our field of view it passes through the cornea, then through the lens, and is projected upside down (a result of light rays crossing while passing through the lens) onto the retina. At the back of the retina is a thin layer of cells comprised of photoreceptors called rods (responsible for detecting changes in light) and cones (capable of determining color) which gather the light and color information, turn it into electrical signals, and pass those signals through the optic nerve to the visual cortex at the back of the brain. (fig. 7)
fig. 7. simplified diagram of the human eye showing that light passes through the cornea, focused by the lens, and projected onto the retina.
This part of the process can be compared to that of a package delivery service. Let’s say that you’ve ordered a set of glass shelves from a company far away from your location and are having them delivered to your home. This particular set of shelves includes hardware from one supplier, special fittings from another, a brushed metal frame from another, and the actual glass shelves from yet another supplier. Each component is packaged at its respective location (the outside world in our analogy) and shipped to a delivery hub. It is there at the hub (our retina) that the packages are sorted and organized (by our rods and cones), and gathered together for shipment to your address. The delivery truck takes the place of our optic nerve; it is responsible solely for getting the packages to the final destination. Once delivered, it is your job to unpackage each box and assemble the shelves correctly; you are left with the task of making sense of what you’ve received. (see fig. 8)
The brain doesn’t see the world as it is, but instead creates mental models through a collection of “aha!” moments.
- Tom Wujec
Once this visual package has been opened, each bit of information is then sent by the occipital lobe to other parts of the brain (up to 30 different areas). For example, information about the identity of an object (what the object is) activates the ventral stream of the temporal lobe, while an object’s location in space (where an object is) activates the dorsal stream, found in the parietal lobe (just above the visual cortex). Other information, such as emotional response to visual stimuli, excites the limbic system which is buried deep in our inner brain |Wujec, 2009|. Tom Wujec, an information designer and Fellow at Autodesk, explains how this mechanical acquisition of visual information begins to be interpreted by our brain, allowing us to recognize and understand what exactly we are looking at: “The brain doesn’t actually see the world as it is, but instead creates a series of mental models through a collection of ‘aha!’ moments, or moments of discovery through various processes” |Wujec, 2009|. He proposes that our eyes visually interrogate our surroundings, constantly acquiring individual aspects which the brain compiles into a unified mental model that represents what we see. In short, the way we make meaning is by covertly “knowing” what we are seeing rather than by overtly identifying everything in sight.
fig. 8. comparison of visual pathway to package delivery service: individual pieces of visual information [shelving components] are picked up by the lens and passed to the retina [hub]. The optic nerve [delivery truck] then carries the information to the visual cortex [package reception] where it is reassembled by the occipital lobe so that we can know [use] what we have seen.