Sensation and Perception Module 18 Vision

Energy=Light We only see a small spectrum of light rays 2 characteristics determine our sensory experiences – Wavelength: the distance from 1 peak of a wave to another; determines color (hue) – Intensity: height of the wavelength; influences brightness

Parts of the Eye – Cornea

Cornea The clear bulge on the front of the eyeball Begins to focus the light by bending it toward a central focal point Protects the eye

Parts of the Eye - Iris

Iris A ring of muscle tissue that forms the colored portion of the eye; creates a hole in the center of the iris (pupil) Regulates the size of the pupil by changing its size--allowing more or less light to enter the eye

Parts of the Eye - Pupil

Pupil The adjustable opening in the center of the eye that controls the amount of light entering the eye (surrounded by the iris) In bright conditions the iris expands, making the pupil smaller. In dark conditions the iris contracts, making the pupil larger.

Parts of the Eye - Lens

Lens A transparent structure behind the pupil; focuses the image on the back of the eye (retina) Muscles that change the thickness of the lens change how the light is bent thereby focusing the image (Accommodation) Glasses or contacts correct problems in the lens’ ability to focus.

The Cosmic Flower Does this picture seem to pulsate? Because the lens of your eye is not perfectly round some parts of what you look at are blurry. Your eyes make micro movements to try to put this entire picture into focus and this creates the pulsation.

Astigmatism Presbyopia Nearsightedness Farsightedness

Parts of the Eye - Retina

Retina Light-sensitive surface with cells that convert light energy to nerve impulses At the back of the eyeball Made up of three layers of cells – Receptor cells (Rods & Cones) – Bipolar cells – Ganglion cells

Parts of the Eye - Fovea

Rods Visual receptor cells located in the retina Can only detect black and white Respond to less light than do cones

Cones Visual receptor cells located in the retina Can detect sharp images and color Need more light than the rods Many cones are clustered in the fovea at the center of the retina.

Rods Cones Watch Blue Man Group’s Rods & Cones Performance

Distribution of Rods and Cones Cones—concentrated in center of eye (fovea) – approx. 6 million Rods—concentrated in periphery – approx. 120 million Stare at a word and you’ll notice the others around it become blurred. (Clear word seen with cones, blurry area seen with Rods) Blind spot—region with no rods or cones

The Hermann Grid Are there gray dots between the squares? Rods in the periphery are responsible for this. When you look at an area directly there is no dot because you are using your cones but the periphery has dots because the rods are trying to do two things, show you there is a dark area and a light area.

Processing Visual Information Rods & Cones transduce light into neural signals. Bipolar cells—neurons that connect rods and cones to the ganglion cells Ganglion cells—neurons that connect to the bipolar cells, their axons form the optic nerve Optic chiasm—point in the brain where the optic nerves from each eye meet and partly crossover to opposite sides of the brain

Visual Processing in the Retina

Parts of the Eye – Optic Nerve

Optic Nerve The nerve that carries visual information from the eye to the thalamus then on to the occipital lobes of the brain

Parts of the Eye – Blind Spot

Blind Spot The point at which the optic nerve travels through the retina to exit the eye (Optic Disk) There are no rods and cones at this point, so there is a small blind spot in vision. We don’t notice our blind spot because each eye compensates for the other or your brain “fills in” the missing background info. (Top-down process) Cover your right eye and stare at the can as you move closer to the screen. Notice the spider disappear in your peripheral vision?

Visual Pathway From the eye to the brain Light travels through… Cornea – Pupil – Lens – Fovea (retina) – Rods/Cones – Bipolar Cells – Ganglion cells (movement & light /color & detail) – Optic Nerve (blind spot) – Optic Chiasm (crossover point) – Thalamus – Occipital Lobe (Primary Visual Cortex)

Feature Detection Nerve cells in the brain fire to a very particular stimulus…like shapes, angles, movement, patterns. – Pass along information to super cell clusters that process more complex patterns – Works with left temporal lobe – Believe super cells come from our ancestors and their survival—natural selection!

Parallel Processing Processing many stimuli at once (motion, color, depth, etc) – “Mrs. M” can’t perceive motion after stoke – Blindsight: illustrate two-track mind.

Color Vision Young-Helmholtz- 3 primary colors: red, green, blue – Trichromatic color theory: based on the stimulation of above 3 color receptors which are found on the retina Color blindness: lacking one or both of these cones Herring: afterimages see opponent color after staring at the one primary color – Opponent process theory: red-green, yellow-blue, black-white. Stimulate one color inhibits the opposite.