As our eyes move from near objects to distant objects, a process known as visual accommodation occurs. Complete adaptation to the dark may take up to 20 minutes.īehind the pupil is the lens, a structure that focuses the incoming light on the retina, the layer of tissue at the back of the eye that contains photoreceptor cells. When we enter a dark movie theater on a sunny day, for instance, muscles in the iris open the pupil and allow more light to enter. The pupil is surrounded by the iris, the colored part of the eye that controls the size of the pupil by constricting or dilating in response to light intensity. The light then passes through the pupil, a small opening in the center of the eye. The Sensing Eye and the Perceiving Visual CortexĪs you can see in Figure 4.7 “Anatomy of the Human Eye”, light enters the eye through the cornea, a clear covering that protects the eye and begins to focus the incoming light. ![]() 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. As you can see in Figure 4.6 “The Electromagnetic Spectrum”, 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. The air around us is filled with a sea of electromagnetic energy pulses of energy waves that can carry information from place to place. 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. Seeing begins when light falls on the eyes, initiating the process of transduction. A large part of our cerebral cortex is devoted to seeing, and we have substantial visual skills. ![]() Whereas other animals rely primarily on hearing, smell, or touch to understand the world around them, human beings rely in large part on 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.Identify the key structures of the eye and the role they play in vision.
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