Vision: How Do We See?

The ability to see and perceive light and color is a remarkable aspect of human vision, governed by the complex workings of our eyes and brain. This phenomenon involves the interaction of light waves with our visual system.

Light is composed of electromagnetic waves, and it behaves both as particles and waves. The visible spectrum, the range of wavelengths perceivable by the human eye, spans from approximately 380 to 750 nanometers. Different colors correspond to different wavelengths, with red having longer wavelengths and violet having shorter ones.

So, how do we perceive these waves?

The human eye plays a crucial role in the process of seeing and perceiving light and color. The eye’s complex structure involves several key components, including the cornea, lens, and retina. When light enters the eye, it passes through the cornea and lens, which focus the light onto the retina at the back of the eye.

Inside the retina exists specialized cells called photoreceptors, responsible for detecting light and transmitting signals to the brain. There are two types of photoreceptors: rods and cones. Rods are sensitive to low light levels and contribute to night vision, while cones are responsible for color vision and function best in well-lit conditions. Regarding the cone cells, there are three types: those sensitive to short (blue), medium (green), and long (red) wavelengths. Through a process called color mixing, the brain combines the signals from these cones to create the vast array of colors that we perceive.

This is in relation to the trichromatic theory. The trichromatic theory, proposed by Thomas Young and refined by Hermann von Helmholtz, asserts that the human eye’s ability to see color results from the combination of signals from the three types of cone cells. This theory laid the foundation for understanding color vision and is supported by extensive experimental evidence.

However, other theories exist as well. Ewald Hering’s opponent-process theory complements the trichromatic theory by proposing that the perception of color is controlled by three opposing systems: red-green, blue-yellow, and black-white. According to this theory, our visual system processes color in a way that opposing colors cannot be perceived simultaneously.

While color is perceived at the retina, the journey of visual information doesn’t end there; it continues through the optic nerve to the brain’s visual processing centers. The brain interprets the signals received and constructs the rich experiences we encounter daily. Areas such as the primary visual cortex and the visual association areas play crucial roles in this process.
The science behind seeing and perceiving light and color is arguably one of the most complex systems in our body. Our eyes, equipped with intricate structures and specialized cells, work in tandem with our brain to construct the vivid and diverse spectrum of colors we experience. The trichromatic and opponent-process theories provide a solid foundation for understanding color vision, showcasing the complexity and beauty of the human visual system.

Sources:
1. https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
2. https://www.optometrists.org/general-practice-optometry/guide-to-eye-health/how-does-the-eye-work/
3. https://www.stanfordchildrens.org/en/topic/default?id=normal-vision-90-P02094
4. https://www.health.harvard.edu/staying-healthy/5-truths-about-protecting-your-eyes (Image Source)

Sean Choi

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