© 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Chapter 4Slide 1 LESSON 4.2 Vision OBJECTIVES Identify and illustrate the structures of the eye that are responsible for vision. Describe the way the brain perceives color.

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Slide 2 Figure 4-1 The Electromagnetic Spectrum

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Slide 3 Structures of the Human Eye The pupil is an opening in the iris that allows light to enter the eye. The iris is a ring of muscles that range in color from light blue to dark brown. The lens is a clear, elastic, disc-shaped structure that refocuses light. The retina is the light-sensitive surface at the back of the eye. The optic nerve carries information from the retina to the brain. The blind spot is the area on the retina where the optic nerve leaves the eye and that contains no receptor cells.

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Slide 4 Figure 4-2 Major Structures of the Human Eye

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Receptor Sites The retina has two kinds of receptors that pick up light. They are Rods and Cones-both named because of their shape. There are 120 million rods per retina and 8 million cones per retina. Rods-respond to varying degrees of light and dark. They are responsible for night vision. Cones allow us to see colors as well as light and dark. Cones are less sensitive to light than rods are. Cones are found mainly in the fovea, where no rods are found. Slide 5

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Importance of Vision Vision is one of our most important senses. 70% of our bodies receptors are located in our eyes Slide 6

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Which person looks friendlier? Slide 7

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Adjusting to Light When it is dark your rods become more sensitive to light. This process is called dark adaptation. It takes about minutes for all of your rods to adjust. When going from dark to light it only takes a matter of a minute for you to adjust to the light and become less sensitive. This is called light adaptation. Slide 8

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Slide 9 Color Vision All the colors you see are red, blue, and green, or a mixture of these three. The color is in your visual system. An object appears as a particular color because it absorbs or reflects certain wavelengths of light. Colors are created by the cones in your eye responding to wavelengths and sending neural signals to your brain, which then creates the colors you see.

Chapter 4 © 2011 South-Western | Cengage Learning A Discovery Experience PSYCHOLOGY Slide 10 Color Blindness Color blindness is a deficiency in the ability to distinguish among colors.