The eye

Living in the dark How do you think you would go being blind? What do you think you would miss the most? Do you think it would be harder being born blind or losing your sight during your life? Why?

Major Structures Of The Human Eye

Structures of the Human Eye The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface and providing 2/3 of the eye's focusing power. The rest is provided by the lens. 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.

How Light Travels through the Eye

Sensation & Perception Don’t “Just Happen” 1. Light bounces off Dilbert 2. Light forms image on retina 3. Image generates electrical signals in receptors 4. Signals travel along nerve fibers to the brain... Perception Signals are processed and you “perceive” Dilbert

Establishing a meaningful distinction between sensation and perception (i.e., sensation and perception are distinct processes. Sensation – the process of gathering information from the environment. Perception – the process of interpreting that information gathered from the environment. The opposing viewpoint is that there is no distinction to be made between sensation and perception. Naïve realism – we can directly know (perceive) the world via the sensory systems.

Where does all of this leave us? The eye is NOT a camera. Correction for inversion is highly-complex and highly-interactive. Perhaps perception is best thought of as a hypothesis test. We make our best guess as to what the retinal image represents.

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.

Light is the Stimulus for Vision Electromagnetic spectrum Energy is described by wavelength Spectrum ranges from short wavelength gamma rays to long wavelength radio waves Visible spectrum for humans ranges from 400 to 700 nanometers Most perceived light is reflected light Thompson Wadsworth

Figure 2.9 The electromagnetic spectrum, showing the wide range of energy in the environment and the small range within this spectrum, called visible light, that we can see. Thompson Wadsworth

Color Blindness Color blindness is a deficiency in the ability to distinguish among colors.

Test for Color Blindness