How We Process Light
Perceiving visual media like text and images requires us to process light. Like sound, light is an invention of sorts, a perception our nervous system creates from traveling energy waves. Specialized cells in the retinas of our eyes absorb electromagnetic energy waves and convert them into a neural signal that our brains interpret as light. Using light, we are able to identify shape, color, depth, and motion—all critical for recognizing the world visually.
Although both sound and light are linked to traveling energy waves, the two kinds of waves are fundamentally distinct. Whereas sound is inherently mechanical, the product of energy created and propagated by movements and vibrations, light measures the electromagnetic energy reflected by an object—something less physical, more passive (Bregman, 1990). This might seem like a rather arcane point, but these differences factor in perception. For example, if we witness a rockslide, both sound and light contribute to our impression, but the sound has a tremendous affect, conveying a physical sense of moving masses hitting the ground. Compared to sound, light affects most of us less palpably, physically, and emotionally. Think about how silent movies seem less gripping than films with sound effects and music.
At the same time, light provides a more durable record than sound. The sound of a rockslide is created by the physical impact of rocks hitting each other and the ground, sending up vibrations that last only a few seconds. However, we can see the fallen rocks on the ground long after the noise has faded away. Whether you look at an object now or five hours from now, it will still be visible.
The visual cortex of the brain is specialized to process light. Cells in the visual cortex are selectively wired to cells in lower-order structures that conduct visual signals, newly converted from electromagnetic energy. Various parts of the visual cortex receive different patterns of input, reflecting their specialized roles in discerning features such as object motion, shape, and color. In addition, certain kinds of visual stimuli, such as letters and faces, are processed in separate regions. For example, processing modules important for reading text are specialized to recognize types of lines—diagonal lines, vertical lines, and curved lines. Modules important for decoding images are specialized to recognize color, texture, and form. Features of different sorts are extracted in parallel, endowing our visual systems with remarkable speed and efficiency.
We now have a basic idea of how light, and therefore the visual input, is processed by the nervous system. To read text and interpret images, we grapple with the strengths and limitations of the visual medium-and we bring our own unique brain networks to the task.
