MODULE #13: VISION

Vision•Transduction: transformation of stimulus energy (light, sound, smells, etc.) to neural impulses our brains can interpret.•Our senses receive the information and then, through transduction, our brains interpret them.

Spectrum of Electromagnetic EnergyThe rest of

these sources of energy are invisible to

us.VisibleSpectru

m

VISION•Wavelength: the distance from one wave peak to the next. It determines the hue.•Amplitude: height of the wave.

VISION•Hue: the color we see.

400 nm 700 nmLong wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

VISIONIntensity: (brightness) Amount of energy in a wave determined by the amplitude.

Different intensities of blue.

The Eye

The Eye•Cornea: where light enters the eye.•Pupil: regulates the amount of light.• Iris: colored ring of muscle, constricts or dilates depending on the amount of light.•Lens: focuses the light rays on the retina.•Acuity: The sharpness of vision.

The Retina •Retina: absorbs light, processes images. Contains rods and cones.•The image formed on your retina is upside down and incomplete.•Your brain fills in information and straightens out the upside down image almost immediately.

The Retina •Rods: detects black & white & allows you to see in low light. Used for night vision.•Cones: detects color & allows you to see in bright light. Most concentrated at the fovea.

The Eye•Normal Vision: Rays of light converge on the retina for both nearby and distant images.

The Eye•Nearsighted: nearby objects are seen more clearly than distant objects.

The light rays from distant objects focus in front of the retina. When it actually reaches the retina, the image is blurry.

I could see

near!

•Farsighted: distant objects are seen more clearly than nearby objects.

The Eye

The light rays from nearby objects focus behind the retina resulting in a blurry

image.

I could see far!

Optic Nerve, Blind Spot & FoveaOptic nerve: Carries neural impulses from the eye to the brain. Fovea: Central point in the retina where cones (no rods) cluster. Point where images focus.Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there.

Let’s find your blind spot!!!!

Optic Nerve, Blind Spot & Fovea

Visual Pathway•Feature detectors: individual neurons in the primary visual cortex/occipital lobes that respond to specific features of a visual stimulus.•Neurons only respond to vertical, horizontal, or diagonal lines. They detect edges, angles, and movement.

Visual Pathway•Parallel Processing: simultaneously analyzing different elements of sensory information, such as color, brightness, shape, etc.•Different parts of the brain are responsible for different functions.

 Color Vision•Young-Helmholtz Trichromatic theory: retina has 3 types of color receptors for red, blue, and green. •Stimulating a combination of these 3 colors results in other colors.•Ex. Stimulating red and green cones produces a yellow image.•People who are color blind have color cones that aren’t functioning.

 Color Vision•Opponent-Process Theory: opposing retinal processes enable color vision. Red & Green, Yellow & Blue, White & Black.•Afterimages: images continue to briefly appear even after the actual image is removed.•Staring at a color will tire that color’s cones and its opponent color appears.

After Images•For the following images, stare at the center of the image until I tell you to stop.•Next, blink and quickly look at the blank white paper and you will see an after image.•You will see the Opponent-Process Theory in action!

Color Constancy•Color depends on context. The three blue disks are identical in color!