visual

• t was Albert Einstein who first proposed that light is actually tiny “packets” of waves. These “wave packets” are called photons and have specific wavelengths associated with them.
• There are three aspects to our perception of light: brightness, color, and saturation.
• Brightness is a determined by the amplitude of the wave – how high or how low the wave actually is. The higher the wave, the brighter the light appears to be. Low waves are dimmer.
• Color, or hue, is largely determined by the length of the wave. Long wavelengths are found at the red end of the visible spectrum. Shorter wavelengths are found at the blue end.
• Saturation refers to the purity of the color people perceive.
• Cornea bends light waves so the image can be focused on the retina.
• Aqueous humor clear liquid that nourishes the eye
• Iris its muscles control the size of the pupil
• Pupil iris opening that changes size depending on the amount of light in the environment
• Lens changes shape to bring objects into focus
• Retina contains photoreceptor cells
• Fovea central area of retina; greatest density of photoreceptors
• Optic nerve sends visual information to the brain
• Blind spot (optic disc) where the optic nerve leaves the eye; there are no photoreceptor cells here
• Vitreous humor jelly-like liquid that nourishes and gives shape to the eye
• Visual accommodation the change in the thickness of the lens as the eye focuses on objects that are far away or close.
• Retina the final stop for light within the eye, a light sensitive area at the back of the eye containing three layers: ganglion cells, bipolar cells, and the rods and cones, special cells that respond to the various light waves.
• The rods and cones are the business end of the retina – the part that actually receives the photons of light and turns them into neural signals to the brain, sending them first to the bipolar cells and then to the retinal ganglion cells whose axons form the optic nerve
• Rods visual sensory receptors found at the back of the retina, responsible for non-color sensitivity to low levels of light.
• Cones visual sensory receptors found at the back of the retina, responsible for color vision and sharpness of vision
• Blind spot area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve, insensitive to light.
• Dark adaptation the recovery of the eye’s sensitivity to visual stimuli in darkness after exposure to bright lights. It occurs as the eye recovers its ability to see when going from a brightly lit state to a dark state.
• Light adaptation the recovery of the eye’s sensitivity to visual stimuli in light after exposure to darkness
• Trichromatic theory (“three colors”) proposed three types of cones: red cones, blue cones, and green cones, one for each of the three primary colors of light.
• Opponent-process theory theory of color vision that process visual neurons 9or groups of neurons) are stimulated by light of one color and inhibited by light of another color.
• Color Blindness is caused by defective cones in the retina of the eye and as a more general term, color-deficient vision is more accurate.
• The Afterimage occurs when a visual sensation persists for a brief time even after the original stimulus is removed.
• Monochrome color blindness people either have no cones or have cones that are not working at all.
• Dichromatic Vision having one cone that does not work properly

  Protanopia (red-green color deficiency) due to the lack of functioning red cones.

  Deuteranopia (another type of red-green color deficiency) results from the lack of functioning green cones
• Tritanopia (blue-yellow color deficiency) these individuals see the world primarily in reds, greens, and shades of gray.
• sight threshold A candle flame at 30 miles on a clear, dark night
• optic nerve, obviously the visual nerve, sensory impulses for sight.
• oculomotor nerve, which moves the eyes, raises eyelids, rotate eyes, adjust amount of light.
• trochlear nerve, smallest cranial nerve – helps control eye movement.
• Light (photoreceptors) -The cells in the retina that respond to light stimuli are an example of a specialized receptor