The Eye contains visual sensory receptors focuses light on the retina contains most of the eye’s cones hole that allows light to enter eye muscle that controls (pupil) how much light enters eye OBJECTIVE 13-2| Describe the major structure of the eye, and explain how they guide the incoming ray of light toward the eye’s receptor cells. transparent outer covering of eye Where optic nerve leaves eye…no receptors here

Hue (color): dimension of color determined by wavelength of light. Wavelength (Hue) Hue (color): dimension of color determined by wavelength of light. Wavelength the distance from the peak of one wave to the peak of the next.

Different wavelengths of light result Wavelength (Hue) Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Long wavelengths Short wavelengths Different wavelengths of light result in different colors.

Intensity (Brightness) Intensity Amount of energy in a wave determined by amplitude; related to perceived brightness.

Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”

The Lens Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects b/c eye elongated & image focus before it hits the retina Farsightedness: A condition in which faraway objects are seen more clearly than near objects b/c eye shortened & image would focus after it hit the retina

Retina The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of other neurons (bipolar, ganglion cells) that process visual information. OBJECTIVE 13-3| Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light.

Fovea Central point in the retina, around which the eye’s cones cluster…because of this there is little color vision in the farthest periphery of our vision http://www.bergen.org Let’s test this fact…

Shares one with other rods Photoreceptors CONES RODS RODS CONES Number 6 million 120 million Location Center (fovea) Periphery Color sensitive? Yes No Sensitivity in dim light? Low High Ability to detect detail? High Low Number of bipolar cells? Each has own Shares one with other rods E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which form the optic nerve (axons). Remember… Cones each have their own bipolar cell. Multiple rods share one bipolar cell.

Test your Blind Spot Blind spot – no visual receptors here because of all the information leaving the eye To find your blind spot, close your right eye and look at the cookie monster at eye level. Maintain your focus on the cookie monster and slowly move your paper from your eyes until the cookie disappears. Under normal circumstances, you are unaware of your blind spot because one eye sees what the other does not. WHY DO YOU SEE WHITE WHERE THE COOKIE SHOULD BE? Even with one eye closed, you're not aware of the gap because your brain "fills in" the missing information by making an assumption about what belongs in the void.

Feature Detection Nerve cells in the visual cortex that respond to specific features, like edges, angle, length and movement. There are even some feature detectors that are specifically sensitive to the human face!

Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. OBJECTIVE 13-5| Discuss parallel processing and discuss its role in visual processing. Movement Aftereffects: *To show you that we have detectors for movement we are going to isolate that detector (and show you how our senses adapt).

from visual cortex to assoc. areas from assoc. areas to memory info sent to visual cortex Tim Bieber/ The Image Bank

Theories of Color Vision Trichromatic theory: Based on behavioral experiments, Helmholtz suggested that retina contains three receptors sensitive to red, blue and green colors. Standard stimulus OBJECTIVE 13-6| Explain how the Young-Helmholtz and opponent-process theories help us understand color vision. Comparison stimulus Max Medium Low Blue Green Red

Photoreceptors Blue Cones Green Cones Red Cones MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans. Short wave Medium wave Long wave

Color Deficiency(blindness) Genetic disorder which prevents individuals from discriminating between certain colors due to a weakness in or lack of one of the cones Most common form of color “blindness” is difficulty distinguishing between red and green Complete color deficiency does exist but is very rare…it would be like watching a black and white movie.

Ishihara (color blindness)Test 25 6 42 5 56 8

Normal vision red/green deficiency Photos from: http://critiquewall.com

Above represent the art in “normal vision”…below what it would look like to a person with red/green deficiency http://www.vischeck.com/examples/

Opponent Process Theory Hering, proposed that we process four primary colors opposed in pairs of red-green, blue-yellow, and black-white. Cones Retinal Ganglion Cells

Afterimages… Gaze at the middle of the flag for about 30 seconds, when it disappears, stare at the dot and report if you see America’s flag.

Gaze at the middle of the light bulb for about 30 Afterimages… Gaze at the middle of the light bulb for about 30 seconds, when it disappears, stare at the white space and report what you see.

Spanish castle afterimage…. Afterimages… Spanish castle afterimage….

Color Constancy the color of an object will remain roughly constant even if the lighting and wavelengths change OBJECTIVE 13-7| Explain the importance of color constancy.