VViissiioonn

Our most Our most dominating dominating

sense.sense.

TransductionTransductionTransduction: Transduction: Conversion of one form of Conversion of one form of energy to another.energy to another.

How is this important when studying sensation?

• Stimulus energies are converted to neural impulses.

Light EnergyLight Energy

What strikes our eyes is What strikes our eyes is not colornot color but but pulses of electromagnetic energypulses of electromagnetic energy that our that our visual system perceives as colorvisual system perceives as color

We only use light energy to see.We only use light energy to see.

The visible spectrum for humans is only a slim portion of the total range of wavelengths. Other animals have different capabilities. For example, many insects can see shorter wavelengths than humans can see. These wavelengths are in the ultraviolet spectrum.

Many fish and reptiles can see longer wavelengths than humans can see. These wavelengths are in the infrared spectrum.

Wavelength = Hue (color)Wavelength = Hue (color)Wavelength: Wavelength: The distance from the peak The distance from the peak of one light wave to the peak of the next.of one light wave to the peak of the next.

•The distance determines the hue (color) of the light we perceive (ex: red vs. blue).

Phase One: Gathering LightPhase One: Gathering Light

The length of the wave gives us its hue (color).The length of the wave gives us its hue (color).ROY G BIVROY G BIVThe longer the wavelength, the more red the hue.The longer the wavelength, the more red the hue.The shorter the wavelength, the more violet the hue.The shorter the wavelength, the more violet the hue.

Amplitude = Intensity (Brightness)Amplitude = Intensity (Brightness)

• Intensity: amount of energy in a light wave

• Determined by the height (amplitude) of the wave.

The higher the wave, the more intense the light is.

Structure of the EyeStructure of the Eye

ScleraScleraThe white part of the The white part of the eyeball is called the eyeball is called the sclerasclera (say: (say: sklairsklair-uh).-uh).– The sclera is made of a The sclera is made of a

tough material and has the tough material and has the important job of covering important job of covering most of the eyeballmost of the eyeball. .

– Look very closely at the Look very closely at the white of the eye, and you'll white of the eye, and you'll see lines that look like tiny see lines that look like tiny pink threads. These are pink threads. These are blood vessels, the tiny blood vessels, the tiny tubes that deliver blood, to tubes that deliver blood, to the sclera.the sclera.

CorneaCorneaThe The corneacornea, , a a transparent dome, sits in transparent dome, sits in front of the colored part of front of the colored part of the eye.the eye.– The cornea The cornea helps the eye helps the eye

focusfocus as light makes its as light makes its way through. way through.

– It is a very important part of It is a very important part of the eye, but you can hardly the eye, but you can hardly see it because it's see it because it's made of made of clear tissueclear tissue. .

Like clear glass, the Like clear glass, the cornea gives your eye a cornea gives your eye a clear window to view the clear window to view the world through.world through.

Iris and PupilIris and PupilBehind the cornea are Behind the cornea are the iris and the pupil.the iris and the pupil.

IrisIris: : is the colorful is the colorful part of the eye. part of the eye. – Iris has muscles Iris has muscles

attached to it that attached to it that change its shape.change its shape.

– This allows the iris to This allows the iris to control how much control how much light goes through light goes through the the pupil.pupil.

– LINK

Iris and PupilIris and PupilPupil:Pupil:is the black circle is the black circle in the center of the irisin the center of the iris--Which is really an --Which is really an opening in the iris, and opening in the iris, and it lets light enter the it lets light enter the eye. eye. – What happens when What happens when

someone flashes a someone flashes a bright light in your bright light in your eyes?eyes?

Lens & RetinaLens & RetinaAfter light enters the pupil, After light enters the pupil, it hits the lens. it hits the lens. LensLens: sits behind the iris : sits behind the iris and is clear and colorless. and is clear and colorless. The lens' job is to The lens' job is to focus focus light rays on the back of light rays on the back of the eyeball the eyeball — a part — a part called the called the retinaretina. . – The lens works much like the The lens works much like the

lens of a movie projector at the lens of a movie projector at the movies. movies.

– Next time you sit in the dark Next time you sit in the dark theater, look behind you at the theater, look behind you at the stream of light coming from the stream of light coming from the projection booth. projection booth.

– This light goes through a This light goes through a powerful lens, which is powerful lens, which is focusing the images onto the focusing the images onto the screen, so you can see the screen, so you can see the movie clearly. In the eye's movie clearly. In the eye's case, however, the film screen case, however, the film screen is your retina.is your retina.

Lens & RetinaLens & RetinaRetinaRetina: : is in the very back is in the very back of the eye. It holds of the eye. It holds millions of cells that are millions of cells that are sensitive to light. sensitive to light. The retina takes the light The retina takes the light the eye receives and the eye receives and changes it into nerve changes it into nerve signalssignals so the brain can so the brain can understand what the eye understand what the eye is seeingis seeing

Ciliary MuscleCiliary MuscleThe lens is suspended in the The lens is suspended in the eye by a bunch of fibers. eye by a bunch of fibers. These fibers are attached to a These fibers are attached to a muscle called the muscle called the ciliaryciliary musclemuscle. . Ciliary muscleCiliary muscle: : has the has the amazing job of amazing job of changing the changing the shape of the lensshape of the lensTry looking away from your Try looking away from your computer and focusing on computer and focusing on something way across the something way across the room. Even though you didn't room. Even though you didn't feel a thing, the shape of your feel a thing, the shape of your lenses changed. lenses changed. When you look at things up When you look at things up close, the lens becomes close, the lens becomes thicker to focus the correct thicker to focus the correct image onto the retina. When image onto the retina. When you look at things far away, you look at things far away, the lens becomes thinner.the lens becomes thinner.

FoveaFovea

The tiny area of The tiny area of sharpest vision sharpest vision in the retinain the retina

ConesCones cluster cluster in and around in and around the foveathe fovea

What happens in the retinaWhat happens in the retina

The The retinaretina is a piece of neural tissue that lines the is a piece of neural tissue that lines the back of the eye…it back of the eye…it absorbs light, processes absorbs light, processes images, images, andand sends information to the brain sends information to the brain..The The visual receptor cellsvisual receptor cells are the are the rodsrods (for black (for black and white and low light vision) and the and white and low light vision) and the conescones (for (for color and daylight vision).color and daylight vision).

• Adaptation, or Adaptation, or becoming more or becoming more or less sensitive to less sensitive to light as needed, light as needed, occurs in part due to occurs in part due to chemical changes in chemical changes in the rods and cones.the rods and cones.

More on Rods and ConesMore on Rods and Cones The retina uses special cells The retina uses special cells called called rodsrods and and conescones to to process light. process light. How many rods and cones How many rods and cones does your retina have?does your retina have?About About 120 million rods120 million rods and and 7 7 million conesmillion cones — in each eye! — in each eye!Rods:Rods: see in black, white, see in black, white, and shades of gray and tell and shades of gray and tell us the form or shape that us the form or shape that something has. something has. – Rods can't tell the difference Rods can't tell the difference

between colors, but they are between colors, but they are super-sensitivesuper-sensitive, allowing us to , allowing us to see when it's very dark.see when it's very dark.

More on Rods and ConesMore on Rods and Cones Cones:Cones: sense color and sense color and they need more light they need more light than rods to work well. than rods to work well. Cones are most helpful Cones are most helpful in normal or bright light. in normal or bright light. – The retina has three types The retina has three types

of cones. of cones. – Each cone type is Each cone type is

sensitive to one of three sensitive to one of three different colors —different colors — red, red, green, or blue green, or blue — to help — to help you see different ranges you see different ranges of color.of color.

– Together, these cones Together, these cones can sense combinations can sense combinations of light waves that enable of light waves that enable our eyes to see millions of our eyes to see millions of colors.colors.

Colored scanning electron micrograph (SEM) of rods (yellow) and cones (green) in the retina of the eye. The outer nuclear layer is purple. Magnification x1800 when printed at 10 centimeters wide.

Rods and Cones - DemoRods and Cones - Demo

Remember that cones cluster in and Remember that cones cluster in and around the fovea (the retina’s area of around the fovea (the retina’s area of central focus). central focus). Because there are low concentrations of Because there are low concentrations of cones (color and fine detail) and higher cones (color and fine detail) and higher concentrations of rods (black, white, gray, concentrations of rods (black, white, gray, and twilight vision) in the periphery of the and twilight vision) in the periphery of the retina, color vision and visual acuity are retina, color vision and visual acuity are poorpoor in the periphery of the visual field in the periphery of the visual field– For example -experiment –128)For example -experiment –128)

Transduction of Light in the RetinaTransduction of Light in the Retina– Optic nerve Optic nerve – –

transports visual transports visual information from the information from the eye to the braineye to the brain

– http://www.youtube.com/watch?v=RE1MvRmWg7I -- X -- X

– http://www.youtube.com/watch?v=gvozcv8pS3c -- X -- X

Conversion Light ImpulsesConversion Light Impulses

Instructor’s Notes

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The Blind SpotThe Blind SpotAxons from the retina to Axons from the retina to the brain converge at the the brain converge at the optic diskoptic disk, a , a hole in the hole in the retina where the optic retina where the optic nerve leaves the eyenerve leaves the eye. . If an image falls on this If an image falls on this hole, it can’t be seen…hole, it can’t be seen…the blind spot.the blind spot.Why don’t we notice this Why don’t we notice this blind spot all the time?blind spot all the time?– The brain makes an The brain makes an

educated guess based educated guess based on what it knows of the on what it knows of the surrounding area – it surrounding area – it fills it in for you.fills it in for you.

Where is your blind spot?Where is your blind spot?

Close your right eye. With your left eye, Close your right eye. With your left eye, look at the +. You should see the red dot look at the +. You should see the red dot in your peripheral vision. Keep looking at in your peripheral vision. Keep looking at the + with your left eye. The red dot will the + with your left eye. The red dot will move from the left to the right and move from the left to the right and disappear and reappear as the dot moves disappear and reappear as the dot moves into and out of your blind spot.into and out of your blind spot.

Transduction ContinuedTransduction ContinuedOnce Once information information reaches the reaches the optic nerve, optic nerve, the optic the optic nerve sends nerve sends the the information on information on to the to the thalamusthalamusThen sent to Then sent to primary visual primary visual cortex.cortex.

In the BrainIn the BrainThe Visual Cortex is located The Visual Cortex is located in the Occipital Lobe of the in the Occipital Lobe of the Cerebral Cortex.Cerebral Cortex.

Feature Detectors Feature Detectors - - specific nerve cells in the brain specific nerve cells in the brain that respond to specific features that respond to specific features of the stimulus, such as shape, of the stimulus, such as shape, angle, or movement.angle, or movement.

Parallel Processing Parallel Processing – the – the processing of many aspects processing of many aspects of a problem simultaneously; of a problem simultaneously; the brain’s natural mode of the brain’s natural mode of information processing for information processing for many functions.many functions.

We have specific cells that respond to specific features of this turkey – to particular edges, lines, angles, and movements. These cells are called feature detectors.

ColorDepth

FormMotion

Trichromatic Theory – Trichromatic Theory – Young and HelmholtzYoung and Helmholtz

Young and Helmholtz, in the mid 1800’s, came up with the first theory of Young and Helmholtz, in the mid 1800’s, came up with the first theory of color vision… color vision… Trichromatic Theory. Trichromatic Theory.

They realized that any color can be created by combining the light waves They realized that any color can be created by combining the light waves of three primary colors:of three primary colors:

So they guessed that we have 3 different types of receptor cells (cones) in So they guessed that we have 3 different types of receptor cells (cones) in our eyes. These 3 types of cones have differing sensitivities to different our eyes. These 3 types of cones have differing sensitivities to different light wavelengths…one for light wavelengths…one for RedRed, one for , one for GreenGreen, and one for , and one for BlueBlue. .

All colors can be seen, according to this theory, All colors can be seen, according to this theory, because of color mixingbecause of color mixing..

http://www.youtube.com/watch?v=Jzl9VPnA3OY

Problems with the Thrichromatic Problems with the Thrichromatic TheoryTheory

Most color-deficient people are not Most color-deficient people are not actually “colorblind” - they simply actually “colorblind” - they simply lack lack cone receptor cells for one or more of cone receptor cells for one or more of these primary colorsthese primary colors. . – Their vision is monochromatic (one color) or Their vision is monochromatic (one color) or

dichromatic (two color) instead of dichromatic (two color) instead of trichromatic.trichromatic.

http://colorvisiontesting.com/ishihara.htm#platecolorvisiontesting.com/ishihara.htm#plate%20with%2057%20answer %20with%2057%20answer

So how is it that those blind to red So how is it that those blind to red and green can often still see yellow? and green can often still see yellow? – This is where the trichromatic theory This is where the trichromatic theory

might become problematic.might become problematic.

Opponent-Process TheoryOpponent-Process TheoryEdward Hering, in 1878, proposed Edward Hering, in 1878, proposed Opponent Process Theory, Opponent Process Theory, which says which says that sensory receptors come in pairs of that sensory receptors come in pairs of colors:colors:– RedRed//GreenGreen– YellowYellow//BlueBlue– BlackBlack/White/White

If one color is stimulated, the other is If one color is stimulated, the other is inhibited.inhibited.

When receptors for a color become When receptors for a color become fatigued, a sort of rebound in the fatigued, a sort of rebound in the receptors produces the opponent color.receptors produces the opponent color.– This explains the concept of This explains the concept of

afterimagesafterimages..

Opponent-Process Theory: Flag 2Opponent-Process Theory: Flag 2

Instructor’s Notes

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Castle Afterimage IllusionCastle Afterimage Illusion

Castle Optical Afterimage Illusion

http://www.youtube.com/watch?v=w6ccBwnc5KU

AfterimagesAfterimages

So which theory of color vision is So which theory of color vision is right?right?

While researchers argued about which was right While researchers argued about which was right for almost a century, most psychologists now for almost a century, most psychologists now agree that it takes agree that it takes both theories both theories to explain color to explain color vision. vision.

Taken together, the two theories explain color Taken together, the two theories explain color vision: the trichromatic theory explains color vision: the trichromatic theory explains color processing in the cones, while the opponent-processing in the cones, while the opponent-process theory explains what happens in cells process theory explains what happens in cells and beyond.and beyond.