Psychology 210Psychology 210

Lecture 4Lecture 4

Kevin R SmithKevin R Smith

VisionVision

Sensory SystemSensory System– The eyeThe eye– Exactly what we sense from our environmentExactly what we sense from our environment

Perceptual SystemPerceptual System– The brainThe brain– How we put together what we sense into a How we put together what we sense into a

visual picturevisual picture

The brain constructs our The brain constructs our environmentenvironment

Multiple experiences of an item Multiple experiences of an item lead to different interpretationslead to different interpretations

The Visual Sensory SystemThe Visual Sensory SystemLight is made of wavesLight is made of waves

WavelengthWavelength– Different colors have different wavelengthsDifferent colors have different wavelengths

AmplitudeAmplitude– Different amplitudes lead to differences in brightnessDifferent amplitudes lead to differences in brightness

Visible spectrumVisible spectrum– 400nm to 750nm400nm to 750nm– ROY G BIVROY G BIV– Short wavelengths are near blue and violetShort wavelengths are near blue and violet– Long wavelengths are near red and orangeLong wavelengths are near red and orange

Properties of Light and WavesProperties of Light and WavesThe color of an object is The color of an object is determined by its abilities determined by its abilities across two dimensionsacross two dimensions– AbsorptionAbsorption– ReflectionReflection

Colors that are reflected Colors that are reflected are the colors that we seeare the colors that we see– A red sweater is red A red sweater is red

because it reflects because it reflects wavelengths that we wavelengths that we perceive as redperceive as red

Other wavelengths would Other wavelengths would be absorbed and NOT be absorbed and NOT visible as a color for this visible as a color for this sweatersweater

Properties of Light and WavesProperties of Light and Waves

Black is a color that Black is a color that absorbs all other absorbs all other colorscolors– ie. It is the absence of ie. It is the absence of

reflected colorreflected color

White is a color that White is a color that reflects all other colorsreflects all other colors– ie. It is the presence of ie. It is the presence of

all colorsall colorsprismsprisms

White object

Properties of Light and WavesProperties of Light and Waves

RefractionRefraction– The change of The change of

direction of the wavesdirection of the wavesOccurs in waterOccurs in water

Different substances Different substances refract light refract light differentlydifferently

The eyeThe eyeScleraSclera– Outer covering that Outer covering that

protects the eye and protects the eye and gives it shapegives it shape

CorneaCornea– Protective covering for the Protective covering for the

eyeeye– Begins to bend the light Begins to bend the light

waves and focus themwaves and focus them

Aqueous humorAqueous humor– Fluid filled area behind the Fluid filled area behind the

corneacornea– Provides nutrients to the Provides nutrients to the

cornea and lenscornea and lens

Parts of the eyeParts of the eyePupilPupil– Area in the center of the eyeArea in the center of the eye– Controls the amount of light that entersControls the amount of light that enters– IrisIris

The muscle that controls the widening or narrowing of the pupilThe muscle that controls the widening or narrowing of the pupil

LensLens– Bend to focus light onto the retinaBend to focus light onto the retina– AccommodationAccommodation

The process of the bending of the lens to properly focus the image on our The process of the bending of the lens to properly focus the image on our retinaretina

Vitreous humorVitreous humor– Gives the eye its shapeGives the eye its shape– Does not regenerateDoes not regenerate

The vitreous humor your born with is what you still haveThe vitreous humor your born with is what you still have– FloatersFloaters

Debris that gathers in the vitreous humor and casts shadows onto the retinaDebris that gathers in the vitreous humor and casts shadows onto the retina

RetinaRetina

Translates light waves into an electrical signal our brain Translates light waves into an electrical signal our brain can processcan processConcaveConcave– Object on retina is translated upside-downObject on retina is translated upside-down

PhotoreceptorsPhotoreceptors– Rods and conesRods and cones

Optic Disk/ Optic NerveOptic Disk/ Optic Nerve– Area in the retina where nerves and blood vessels exit the eyeArea in the retina where nerves and blood vessels exit the eye– Forms a blind spotForms a blind spot

FoveaFovea– Area in center of retinaArea in center of retina

Layers of the RetinaLayers of the RetinaFour main types of Four main types of visual processing visual processing neuronsneurons– Ganglion cell layerGanglion cell layer– Amacrine and Amacrine and

bipolar cell layerbipolar cell layer– Horizontal cellsHorizontal cells

Visual Sensory Visual Sensory NeuronsNeurons– PhotoreceptorsPhotoreceptors

RodsRodsConesCones

Rods and ConesRods and Cones

Where a sensory signal Where a sensory signal (light waves) gets (light waves) gets changed into electrical changed into electrical energyenergy– Process called Process called

transductiontransduction

RodsRods– Sensitive to black and Sensitive to black and

whitewhite– Most of them in peripheryMost of them in periphery

ConesCones– Sensitive to colorSensitive to color– Most of them in foveaMost of them in fovea

RodsRods

Contain rhodopsinContain rhodopsin

120 million in a 120 million in a human eyehuman eye

Responsible for Responsible for night vision night vision

Very sensitive to Very sensitive to lightlight

Very poor clarityVery poor clarity

ConesCones

6 million in the 6 million in the human eyehuman eye

Responsible for Responsible for vision in bright vision in bright lightlight

Excellent clarityExcellent clarity

3 different types 3 different types with different with different pigmentspigments

ConesCones

Three different typesThree different types– Blue, shortBlue, short– Green, mediumGreen, medium– Red, longRed, long

Horizontal CellsHorizontal CellsIntegrate Integrate information from information from the the photoreceptorsphotoreceptors

Transfer that Transfer that information to information to bipolar cellsbipolar cells

Bipolar cellsBipolar cells

Receive input from Receive input from horizontal cells and horizontal cells and photoreceptorsphotoreceptors

Transmit information Transmit information to amacrine cellsto amacrine cells

Contain receptive Contain receptive fieldsfields– Antagonistic center-Antagonistic center-

surround organizationsurround organizationphotoreceptors

Horizontal cellsBipolar cells

Amacrine Cells

Amacrine CellsAmacrine Cells

Respond to changes Respond to changes in the visual in the visual environmentenvironment

Connect bipolar cells, Connect bipolar cells, ganglion cells, and ganglion cells, and other amacrine cellsother amacrine cells

Ganglion cellsGanglion cells

Receive input from bipolar and amacrine Receive input from bipolar and amacrine cellscells

Same center-surround receptive fields Same center-surround receptive fields found in bipolar cellsfound in bipolar cells

On-center bipolar fields connect to on-On-center bipolar fields connect to on-center ganglion cellscenter ganglion cells

Off-center bipolar fields connect to off-Off-center bipolar fields connect to off-center ganglion cellscenter ganglion cells

What do receptive fields do?What do receptive fields do?

On-center and off-center fields provide for On-center and off-center fields provide for greater acuitygreater acuity

Large unchanged surfaces don’t activate Large unchanged surfaces don’t activate the neurons as well as changing surfaces the neurons as well as changing surfaces with lines, cracks, and endswith lines, cracks, and ends