VISIONVISION

From Light to SightFrom Light to Sight

ObjectiveObjective

To describe how the receptor cells for To describe how the receptor cells for vision respond to the physical energy of vision respond to the physical energy of light waves and are located in the retina of light waves and are located in the retina of the eye.the eye.

Focus QuestionsFocus Questions

What is the visible spectrum?What is the visible spectrum?

What are the key structures of the eye and What are the key structures of the eye and their functions?their functions?

What are rods and cones, and how do What are rods and cones, and how do their functions differ?their functions differ?

What We SeeWhat We See

Light is only one kind of Light is only one kind of electromagnetic energy. electromagnetic energy. Electromagnetic energy Electromagnetic energy sources differ in sources differ in wavelength.wavelength.Humans are only Humans are only capable of seeing only a capable of seeing only a miniscule portion of miniscule portion of electromagnetic energy.electromagnetic energy.

How We SeeHow We SeeLight waves reflected from an object pass Light waves reflected from an object pass through the cornea, pupil and lens.through the cornea, pupil and lens.

What happens when you What happens when you look at an object?look at an object?

Scattered Scattered lightlight from the object enters through from the object enters through the cornea. the cornea.

The light is projected onto the retina. The light is projected onto the retina.

The retina sends messages to the brain The retina sends messages to the brain through the optic through the optic nervenerve. .

The The brainbrain interprets the object. interprets the object.

CorneaCornea

A clear membrane covering the visible part A clear membrane covering the visible part of the eye that helps gather and direct of the eye that helps gather and direct incoming light. incoming light.

PupilPupil

The opening In The opening In the middle of the the middle of the iris that changes iris that changes size to let in size to let in different amount different amount of light.of light.

LensLens

A transparent structure located behind the A transparent structure located behind the pupil that actively focuses, or bends, light pupil that actively focuses, or bends, light as it enters the eye.as it enters the eye.

Some Of Us See Life Through This Some Of Us See Life Through This Lens.Lens.

IrisIris

The colored part of the eye, which is the The colored part of the eye, which is the muscle that controls the size of the pupil.muscle that controls the size of the pupil.

What happens when you What happens when you look at an object again?look at an object again?

Scattered Scattered lightlight from the object enters through from the object enters through the cornea. the cornea.

The light is projected onto the retina. The light is projected onto the retina.

The retina sends messages to the brain The retina sends messages to the brain through the optic through the optic nervenerve. .

The The brainbrain interprets the object. interprets the object.

Receptor CellsReceptor Cells

These cells are present in every sensory These cells are present in every sensory system to change (transduce) some other system to change (transduce) some other form of energy into neural impulses.form of energy into neural impulses.

In sight they change light into neural In sight they change light into neural impulses the brain can understand.impulses the brain can understand.

Visual system has two types of receptor Visual system has two types of receptor cells – rods and cones.cells – rods and cones.

RetinaRetina

A thin light-sensitive membrane A thin light-sensitive membrane located at the back of the eye that located at the back of the eye that contains the sensory receptors for contains the sensory receptors for vision.vision.

Retina – back of the eye.Retina – back of the eye.

Rods and ConesRods and Cones

Sensory Sensory receptors receptors for light for light that are that are contained contained within the within the retina. retina.

Visual receptor Visual receptor cells located in cells located in the retinathe retina

Can detect Can detect sharp images sharp images and colorand color

Need more Need more light than the light than the rodsrods

ConesCones

Visual Visual receptor receptor cells located cells located in the retinain the retina

Can only Can only detect black detect black and whiteand white

Highly Highly sensitive to sensitive to lightlight

RodsRods

FoveaFovea

The central focal point of the retina.The central focal point of the retina.

The spot where vision is best (most The spot where vision is best (most detailed).detailed).

Fovea – composed entirely of Fovea – composed entirely of conescones

Fovea - ExampleFovea - Example

There are no rods in the fovea. Images that do There are no rods in the fovea. Images that do not fall on the fovea tend to be perceived as not fall on the fovea tend to be perceived as blurry or indistinct. For example, focus your blurry or indistinct. For example, focus your eyes of the word eyes of the word For For at the beginning of this at the beginning of this sentence. In contrast to the sharpness of the sentence. In contrast to the sharpness of the letters in letters in ForFor, the words to the left and right will , the words to the left and right will become comparatively blurry. The image of the become comparatively blurry. The image of the outlying words is striking the peripheral areas of outlying words is striking the peripheral areas of the retina, where rods are more prevalent and the retina, where rods are more prevalent and there are very few cones.there are very few cones.(handout)(handout)

The Blind The Blind SpotSpot

The Other Blind SpotThe Other Blind Spot

The Blind Spot - DefinitionThe Blind Spot - Definition

An area of the retina without rods and An area of the retina without rods and cones, where the optic nerve leaves the cones, where the optic nerve leaves the eye (known as the optic disc), producing a eye (known as the optic disc), producing a small gap in the field of vision. small gap in the field of vision.

If you don’t believe me just ask the spider If you don’t believe me just ask the spider (handout).(handout).

Processing Visual InformationProcessing Visual Information

Key ThemesKey Themes

Signals from the rods and cones undergo Signals from the rods and cones undergo preliminary processing in the retina before preliminary processing in the retina before they are transmitted to the brain.they are transmitted to the brain.

Key QuestionsKey Questions

What are the bipolar and ganglion cells What are the bipolar and ganglion cells and how do their functions differ?and how do their functions differ?

How is visual information transmitted from How is visual information transmitted from the retina to the brain?the retina to the brain?

What properties of light correspond to What properties of light correspond to color perceptions, and how is color vision color perceptions, and how is color vision explained?explained?

Ganglion CellsGanglion Cells

Where preliminary processing occurs.Where preliminary processing occurs.

Found in the retina where specialized Found in the retina where specialized neurons connect to bipolar cells. neurons connect to bipolar cells.

Made possible by a bit of brain tissue that Made possible by a bit of brain tissue that migrates to the eye during fetal migrates to the eye during fetal development.development.

Ganglion cells = purple bulbsGanglion cells = purple bulbs

Bipolar CellsBipolar Cells

In the retina, they are the specialized In the retina, they are the specialized neurons that connect the rods and cones neurons that connect the rods and cones with the ganglion cells.with the ganglion cells.

Bipolar Cells = Gold bulbsBipolar Cells = Gold bulbs

From Eye to BrainFrom Eye to BrainRods and cones receive Rods and cones receive light.light.They signal the bipolar They signal the bipolar cells.cells.Then the bipolar cells Then the bipolar cells funnel to the ganglion funnel to the ganglion cells.cells.Finally the ganglion cells Finally the ganglion cells (all bundled together (all bundled together make up the optical nerve) make up the optical nerve) process the information process the information and send it to the brain.and send it to the brain.

The Optic ChiasmThe Optic Chiasm

The point in the The point in the brain where the brain where the optic nerve fibers optic nerve fibers from each eye from each eye meet and partly meet and partly cross over to the cross over to the opposite side of opposite side of the brain.the brain.

The Optic ChiasmThe Optic Chiasm

Where the left and right optic nerves meet.Where the left and right optic nerves meet.

Most of the optic nerve axons project Most of the optic nerve axons project straight to the thalamus. straight to the thalamus.

From the thalamus, the impulses are then From the thalamus, the impulses are then sent straight to the visual cortex where sent straight to the visual cortex where they are decoded and interpreted. they are decoded and interpreted.

Color VisionColor Vision

Our experience of color involves three Our experience of color involves three properties of the light wave.properties of the light wave.

HueHue

SaturationSaturation

BrightnessBrightness

My Favorite ColorsMy Favorite Colors

HueHue

The property of wavelength of light known as The property of wavelength of light known as color. color.

Different wavelengths correspond to our Different wavelengths correspond to our subjective experiences of different colors.subjective experiences of different colors.

700 nanometers is considered to be pure red.700 nanometers is considered to be pure red.

400 nanometers is pure violet.400 nanometers is pure violet.

SaturationSaturationThe property of color that corresponds to The property of color that corresponds to the purity of the lightwave. the purity of the lightwave.

Pure red, produced by a single Pure red, produced by a single wavelength, is more saturated than pink wavelength, is more saturated than pink (red plus white).(red plus white).

BrightnessBrightnessThe perceived intensity of a color which The perceived intensity of a color which corresponds to the amplitude of the light corresponds to the amplitude of the light wave.wave.

The higher the amplitude the greater the The higher the amplitude the greater the brightness.brightness.

Trichromatic Theory of Color VisionTrichromatic Theory of Color Vision

Sensation of color results because cones Sensation of color results because cones in the retina are especially sensitive to red in the retina are especially sensitive to red light, green light or blue light.light, green light or blue light.

Color BlindnessColor Blindness

One of several inherited forms of color One of several inherited forms of color deficiencies in which an individual cannot deficiencies in which an individual cannot distinguish between certain colors. distinguish between certain colors.

Want to take the test?Want to take the test?

Test PlateTest Plate

What Number Do You See?What Number Do You See?

Trace a line from one “x” to the other. Trace a line from one “x” to the other.

Opponent-Process TheoryOpponent-Process Theory

Color vision is the product of opposing Color vision is the product of opposing pairs of color receptors, red/green, pairs of color receptors, red/green, blue/yellow, and black/white.blue/yellow, and black/white.

When one member of the pair is When one member of the pair is stimulated, the other is inhibited. stimulated, the other is inhibited.

AfterimageAfterimage

A visual experience that occurs after the A visual experience that occurs after the original source of stimulation is no longer original source of stimulation is no longer present.present.

Afterimage – Page 95Afterimage – Page 95

The EndThe End

Afterimage handout

Pillow Fight

Too cool for eye

protection

Not Injured

From a sparkler on the 4th

of July

PLEASE protect

your eyes.