Learning Objectives
- Identify the key structures of the eye and the role they play in vision.
- Summarize how the eye and the visual cortex work together to sense and perceive the visual stimuli in the environment, including processing colors, shape, depth, and motion.
Whereas other animals rely primarily on hearing, smell, or touch to understand the world around them, human beings rely in large part on vision. A large part of our cerebral cortex is devoted to seeing, and we have substantial visual skills. Seeing begins when light falls on the eyes, initiating the process of transduction. Once this visual information reaches the visual cortex, it is processed by a variety of neurons that detect colors, shapes, and motion, and that create meaningful perceptions out of the incoming stimuli.
The air around us is filled with a sea of electromagnetic energy; pulses of energy waves that can carry information from place to place. As you can see in Figure 4.3, electromagnetic waves vary in their wavelength—the distance between one wave peak and the next wave peak, with the shortest gamma waves being only a fraction of a millimeter in length and the longest radio waves being hundreds of kilometers long. Humans are blind to almost all of this energy—our eyes detect only the range from about 400 to 700 billionths of a meter, the part of the electromagnetic spectrum known as the visible spectrum.
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