AP PSYCH Unit 4.2 Vision 1. How does the eye transform light energy into neural messages? 2. How does the brain process visual information? 3. What theories help us understand color vision? 4. Is your red the same as my red? 5. Are you color blind?
The Stimulus Input: Light Energy Transduction (transform) conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells into neural impulses our brains can interpret. We don t actually see color, but pulses of electromagnetic energy we perceive as color
Wavelength Physical characteristic of light that helps us determine our sensory experience of them The distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of comic rays to the long pulses of radio transmission.
Hue The dimension of color that is determined by the wavelength of light what we know as the color names blue, green, and so forth. Wavelength determines hue
Intensity The amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the wave s amplitude. Wave s amplitude (height) determines the intensity
Electromagnetic Energy Spectrum
The Structure of the Eye Cornea - Outer covering of the eye. Light enters through cornea. Protects the eye. Bends light to provide focus.
The Structure of the Eye Then light passes through the Pupil - the small adjustable opening in the center of the eye.
The Structure of the Eye -Iris is the color in your eye -The iris is so distinctive that it can confirm your identity! Iris - a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening. The iris dilates/constricts in response to changing light intensity or even emotions
Can pupils dilate just because of emotions (not just the light)? Let s test our Primary & Secondary Pupillary Response
Did it work?
The Structure of the Eye Lens - the transparent structure behind the pupil that changes shape to help focus images on the retina.
The Structure of the Eye Retina - the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
Accommodation The process by which the eye s lens changes shape to focus near or far objects on the retina. -the ways the muscles of the eye change the shape of the lens to focus light onto the retina (you will get a totally different definition of accommodation in unit 9 )
The Structure of the Eye Alternate View
The Retina Rods and Cones Cones Rods
Rods vs Cones Rods retinal receptors that detect black, white, & gray; necessary for peripheral and twilight vision, when cones don t respond Cones retinal receptor cells that are concentrated near the center of the retina and function in daylight or well-lit conditions. The cones detect fine detail & give rise to color sensations. Some animals have more rods than cones good night vision, poor color vision (think about animals you know )
Rods vs Cones Let s test our rods, cones, peripheral vision, and foveal vision with a few experiments
Bipolar Cells, Ganglion Cells, Optic Nerve, Blind Spot Bipolar cells are activated by neural signals from rods & cones Ganglion cells activated by bipolar cells Axons from Ganglion cells come together like strands of a rope to form the optic nerve and are carried to the brain, then to thalamus, then eventually to visual cortex Optic nerve has 1 million ganglion fibers, can send 1 million messages No receptor cells at the back of the eye creating a blind spot Brain fills in blind spot holes without you knowing it
The Retina s Reaction to Light
Blind spot cover your left eye and look at the black dot on the left. Move back and forth until the cross disappears. Did it work?!
The Structure of the Eye Optic Nerve - the nerve that carries neural impulses from the eye to the brain.
The Structure of the Eye Blind Spot - the point at which the optic nerve leaves the eye, creating a blind spot because no receptor cells are located there.
The Structure of the Eye Fovea - the central focal point in the retina, around which the eye s cones cluster. Objects in the center of your vision are more focused than peripheral objects
Pathways from the eyes to the visual cortex
Same sensitivity that enables retinal cells to fire messages can lead to misfire, too Turn your eyes to the left Close them Rub the right side of your eyelid See a patch of light to the left? Why?
Visual Information Processing Feature detectors - nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.
Feature Detectors fmri scans show certain brain areas lighting up depending on what they are looking at Scientists can tell if people are looking at a shoe, a face, etc by what part of brain lights up If region responsible for perceiving faces is damaged, you could recognize other objects, just not faces
Parallel Processing The processing of many aspects of a problem simultaneously; the brain s natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving. Damage to a certain part of brain responsible for a certain parallel processing task experience problems, for example, might see color, but can t detect motion, people just disappear and reappear to new spots
Parallel Processing This is more complex than taking apart a car, piece by piece, transporting it to a different location, then having different specialized workers put it back together. And this happens instantly & effortlessly
Color Vision Is a tomato red? It is everything but red, it reflects long wavelengths of red Red is our mental construction of red, the wavelengths don t have color, our brain constructs the color (how can we dream in color??) We can see 7 million different hues But 1 in 50 is color deficient, and that person is usually male
Color Vision Young-Helmholtz trichromatic (three color) theory - the theory that the retina contains three different color receptors one most sensitive to red, one to green, one to blue which, when stimulated in combination can produce the perception of any color. When we combine these, we get all the other colors Red Green - Blue Monochromatic vision, dichromatic vision deficiency in amount of cones, don t see all 3 colors, (true name for being colorblind )
Opponent-Process Theory Why doesn t mixing red and green paint make yellow? It seems like more of a pure color, unlike purple which seems like a mix of blue and red? There must be additional color processes at work OP Theory states that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green. Explains afterimage, let s try:
Afterimage