IVC Psyc 1 Fall 2010 Lecture 4 (Sensation Perception)

8/8/2019 IVC Psyc 1 Fall 2010 Lecture 4 (Sensation Perception)

1/94

On Todays Show

1. Introduction to sensation vs. perception

2. Absolute threshold

3. The Just-noticeable-difference

4. Signal Detection Theory

5. The Trichromatic Theory of Color Vision

6. The Opponent-Process Theory of Color Vision

7. Perception: Perceptual Constancies

8. The Gestalt approach to grouping


2/94

Makes sense?


3/94

Makes sense?


4/94

Makes sense?


5/94

Sensation vs. Perception

Whats the difference between sensation and

perception?

Sensation is simply the receiving ofinformation from our senses.

a process by which our sensory receptors and nervoussystem receive and represent stimulus energy (textbookdefinition)

Sensation requires that events in the worldbe converted to another form.


6/94


In the case of sensation, physical events are

converted toneural impulses.

Sensations must be converted toperceptions, the set of processes by whichwe recognize, organize, and make sense of thesensations we receive.

a process of organizing and interpreting sensoryinformation, enabling us to recognize meaningful objectsand events (textbook definition)

In other words:

Perception =sensation +interpretation


7/94


ILOVE

PARIS IN THETHE SPRINGTIME


8/94


Aoccdrnig to a rscheearch atCmabrigde Uinervtisy, it deosn't

mttaer in waht oredr the ltteers ina wrod are, the olny iprmoetnt

tihng is taht the frist and lsat ltteerbe at the rghit pclae. The rset canbe a toatl mses and you can sitll

raed it wouthit porbelm. Tihs isbcuseae the huamn mnid deos notraed ervey lteter by istlef, but the

wrod as a wlohe.


9/94



10/94

Movie Time!

Isense a film coming onIsense a film coming on


11/94

Sensation

Three questions arise:

1. Detection: how sensitive are our senses?

2. Discrimination: how do changes inphysicalstimulationaffectour sensations?

3. Scaling: whatisthe relationbetweenthe physicalworldandour psychologicalperception ofit?

These three questionsgave rise tothe studyofpsychophysics.

Psychophysics isthe studyofthe relationshipbetweenthephysicalcharacteristics ofstimuliandthe consciouspsychologicalexperiencesassociatedwiththem.


12/94

Absolute Threshold

Aquestion ofdetection: what is the smallest amount of

stimulation that a person can sense?The absolute threshold is the minimum amount of stimulationthat an individual can detect 50% of the time through a givensense.

Vision:

A candle flame at 30 miles on a clear, dark night


13/94

Absolute Threshold



Hearing:

The tick of a watch at 20 feet in a quiet room


14/94

Absolute Threshold



Smell:

One drop of perfume diffused in a 3-bedroomapartment


15/94

Absolute Threshold



Taste:

One teaspoon of sugar in 2 gallons of water


16/94

Absolute Threshold



Touch:

The wing of a fly falling on your cheek from adistance of 1 centimeter


17/94

Subliminal Stimulation

When stimuli are detectable less than 50%of the time, they are

subliminal.Subliminal literally means below threshold.

Can we perceive subliminalstimulation?

Yes.

Can we be persuaded by

subliminal messages?

Not really

Actress Kim Novak wants you to buy popcorn

when you watch "Picnic."


18/94

18

Subliminal Stimulation

Can we be persuaded by subliminal messages?

Not really

Can we at least create associations fromsubliminal stimuli? Yes!


19/94

Subliminal Film

Youll only see this film less than 50%of the time.


20/94

Difference Threshold

Aquestion ofdiscrimination: what is the smallest difference in a

stimulation that a person can sense?The difference thresholdor the Just Noticeable Difference(JND) is the minimum amountof change in a stimulation that anindividual can detect through a given sense.


21/94





22/94





23/94





24/94





25/94





26/94





27/94





28/94





29/94


ErnstWeber Gustav Fechner

The Weber-Fechner Law states thatthe intensitybywhichthe standardmust be increased to be noticedis proportional

to the intensityofthe standard.


30/94

SensoryAdaptation

Jump in the ocean

COLD!!!Stay in the water for a while, and what happens?

It doesnt feel so cold anymore

Why?

Sensory Adaptation - diminished sensitivity as

a consequence of constant stimulation

Touch, smells, tastes, sounds

Vision?


31/94

SensoryAdaptation

Vision so if we stare at an object without flinching, does itvanish from our sight?

No because our eyes are always moving


32/94

Vision

Whatdo we see? Light.

Humans only see the visible spectrum, a very small portion ofthe electromagneticspectrum, from ~ 400-700 nanometers.


33/94

Vision

Howdo we see light?

Wavelength causes us tosee lightas certaincolors.

Amplitude causes us to seelightatcertain levels ofbrightness.


34/94

The Eye

The cornea protects

the surface ofeye

The lens allowsforaccommodation:

Distantimageflattens

Close image thickens

The iris regulates

lightintothe eye

pupil= keyhole intodarkroom


35/94

The Eye

The retina transduces

electromagneticradiationintoneuralimpulses.

The image onthe retina isupside-down& backward.


36/94

The Eye

The Retina

Fovea The fovea isthe center oftheretina.

Whenwe look directly atanobjectitisfocused onthe fovea.

The fovea hasthe greatestreceptordensity.

Receptors

Cones Colorreceptors

Highest concentrationinthe fovea.

Rods Light (nocolor)receptors

None inthe fovea.

Highest concentrationinthe periphery.

(blind spot)


37/94

The Eye

The Retina

R

eceptors Cones Colorreceptors

Highest concentration in thefovea.

Rods Light (nocolor)receptors

None in the fovea.

Highest concentration in the

periphery.

-The Blind Spot Where theopticnerve leavesthe eye andthere are NOreceptors


38/94


39/94

The Eye

Receptors in the Human Eye

Cones Rods

Number

Location in

retina

Sensitivity in

dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million


40/94

The Eye

The majorityofourreceptors

are inourfovea,andare activewhenwe lookdirectlyatsomething.

Surroundingreceptorsaremore sparselydistributed.

Theygive youasomewhatfuzzy,inaccurate image.

Anactive receptorisanhonestreceptor,sotheblackdotsfade whenyou

focusrightonthem.

The blackdotsare proofthatyoucansee withperipheralreceptors, butyoushouldn'talwaystrust

them.

Try to count the black dots!


41/94

The Pathway to theVisual Cortex


42/94

Theories ofVision

The Young-Helmholtz Trichromatic Theory of ColorVision:

Eventhoughwe candiscriminate amongmanydifferentcolors,we onlyhave three typesofreceptors:

RED GREEN BLUE

Usingthese three receptors,ourbrainscanrecognize some10,000,000differentcolors.


43/94

Theories ofVision

The Young-Helmholtz Trichromatic Theory of Color Vision:

Eventhoughwe candiscriminate amongmanydifferentcolors,we onlyhave three typesofreceptors:

red bluegreen

How in the h#!! do we use only 3 colors by this, I mean red,

green and blue?We have to take a lookat color mixing.

C l Mi i


44/94

ColorMixing

Subtractive color mixing

e.g. paintor dye

mix of all pigment primaries= all light absorbed

mudd

y black produced

Additive color mixing

e.g. light (TV)

mix of all lightprimaries = all lightpresent

white produced

Red

Paint

Blue

PaintYellow

Paint

T i h i Th


45/94

Trichromatic Theory

Trichromatic Theory

our visual system producescolors like a television set

Red

Paint

Blue

PaintYellow

Paint

T i h ti Th


46/94

Trichromatic Theory

Color Blindness

Some people have damage toone of their cones: Dichromats have only two working cones

If theyre missing either redor green, they have red-green color blindness (75% missinggreen, 24% missing

red)

T i h ti Th


47/94

Trichromatic Theory

Color Blindness

Some people have damage toone of their cones:

Dichromats have only two working cones

If theyre missing blue, they see the world in shades ofonly red and green (1%of dichromats)

T i h ti Th


48/94

Trichromatic Theory

Color Blindness

Some people, monochromats, can only see in black and white:

Blue

PaintYellow

Paint

Trichromatic Theor


49/94

Trichromatic Theory

Color Blindness

Testing for color blindness (10%of males in the world):

Theories of Vision


50/94

Theories ofVision

The Hering Opponent-Process Theory of Color Vision:

Problem: nothingiseverreddish-greenoryellowish-blue.Answer: red-greenformanopponentpair,asdoyellow-blue.

We have three opponentpairs:red

Red

Yllo

Blu Blk

WhtGrn

Firingone halfof the pair repeatedly results in fatigue. This

explains the existence of complementary afterimages.

Opponent Process Theory


51/94

Opponent-Process Theory

Opponent-P

rocess Theory-

opposing retinalprocesses enable color vision

ON O FF

red green

green red

blue yellow

yellow blue

black whitewhite black



52/94


Complementary afterimages:





53/94


Complementary afterimages:



Gestalt Approaches to Perception


54/94

GestaltApproaches to Perception

Separation of Objects

Grouping isthe processoffiguring outwhatpiecesoftheimage belongtogether.

Gestalt (form orwhole) Psychologistswere interested inunderstandinghowthe people decided howthingsgotogetherin

groupsbased uponthe relationshipsthey see betweenperceptualelements.

The whole

may exceedthe sumofitsparts.



55/94


Separation of Figure & Ground

We see the figure in theforeground.

- Invision, thefigure seems more solid.

Inboth visionandaudition, the figure is

usually the object ofinterest.

We see the groundin the background.

Something cannot be seenas both figureandgroundsimultaneously.



56/94





57/94





58/94





59/94





60/94





61/94


Grouping by proximity.

When we perceive an assortmentofobjects, we tendto see objects that are close to each other as forming agroup.

We tend to see this as four pairs of circles, rather than eightcircles, or two pairs of four.

We see this as one group of 2and one group of3, ratherthan 5 items.



62/94


Grouping by similarity.

When we perceive an assortmentofobjects, we tendgroup like objects together.

We tend to see this as two rowsofdarkcircles and two rows oflight circles, rather than six rows

of four or six groups of four.

We tend to see this as two rowsof circles and two rows ofsquares, rather than six rows of

objects.

we tend to see the redstars as being partofone figure, and the blue squares asbeing partof another.



63/94


We tend to see this as a verticalline crossed by a horizontal line,

rather than four separate linesmeeting at a center point, or twocorners.

Perception of continuity.

We tend to perceive smoothlyflowingor continuousformsrather than disrupted or discontinuousones.



64/94


We tend to see this as a verticalline crossed by a horizontal line,

rather than four separate linesmeeting at a center point, or twocorners.

Perception of continuity.

We tend to perceive smoothlyflowingor continuousformsrather than disrupted or discontinuousones.



65/94


Perception of connectedness.

Because they are uniform and linked, we perceiveeach of the spots and lines as a single unit.



66/94


Perception of closure.

We tend toperceptuallyclose up,orcomplete,objectsthatare notin factcomplete.

We tend tosee thisasacircle,and two triangles,rather than abunchofbroken linesand some Pac-Men havingaget-together.



67/94


Grouping Principlesproximity--group nearby figures togethersimilarity--group figures that are similar

continuity--perceive continuous patterns

closure--fill in gaps

connectedness--spots, lines, and areas are seen asunit when connected

closure

Depth Perception


68/94

Depth Perception

Depth Perception

ability to see objects in three dimensions

allows us to judge distance

Depth Perception


69/94

Depth Perception

Depth cues are generally either binocular (utilizing both eyes) ormonocular (utilizingone eye).

Binocular Cues (requiring both eyes)

Binocular convergence iscuedby your two eyes turning

inwardas objects approachyou.

close objects result in strongmuscle commands andstrongneural signals, far objects

result in weak musclecommands andweak neuralsignals.

Depth Perception


70/94

Depth Perception


Binocular Cues (requiring both eyes)

Binocular convergence iscuedby your two eyes turning

inwardas objects approachyou.

Retinal disparity is cuedbythe differing images each eyesends to the brain.

The further away something is,the less disparity is noticed.

Depth Perception


71/94

Depth Perception

Binocular Cues allow us to see in 3-D.

Depth Perception


72/94

Depth Perception


Depth Perception


73/94

Depth Perception


Depth Perception


74/94

Depth Perception


Monocular cues (requiringone eye)

relative size: smaller objects must be further away.

interposition: the firstoverlappingobjectmust be closer.

relative height: objects closer to the horizon must be further away.

linear perspective: apparently parallel lines seemtoconverge in thedistance.

aerial perspective: clear images are closer,fuzzy images are furtheraway.

motion parallax: bigandmoving quickly =closer; small andmovingslowly =further away.

Light and shadow: dimmer objects seemfurther away,we assume thatlightcomes fromabove.

Depth Perception


75/94

Depth Perception

Relative size

Interposition

Relative height

Linearperspective

Aerial

perspective

Motion Parallax

Light/shadow

Perceptual Constancy


76/94


Perceptual Constancy isthe abilitytomaintainaperceptionofthe underlyingphysicalcharacteristicsofanobject(e. g.,size,shape, orcolor)despite drasticchangesinthe sensorymanifestationsofthe object.



77/94


Size Constancy refersto ourperceptionofunchangingsize with

distance. Perceivedsizedependsupon:

The size ofthe

retinal image.

The perceiveddistance betweentheobserverandthe

object.



78/94

e cep ua Co s a cy

Shape Constancy refersto ourperceptionthatanobjectsshape remainsthe same despite changesinorientation.



79/94

p y

Depth Perceptionrefersto ourabilityto

interpretvisualinformationinthree-dimensionalspace,providinginformation

aboutanobjectsdepth.

Contradictorydepthinformationindifferentsectionsofthe picturecause conflict.



80/94

p y

Depth Perceptionrefersto ourabilityto

interpretvisualinformationinthree-dimensionalspace,providinginformation

aboutanobjectsdepth.

Contradictorydepthinformationindifferentsectionsofthe picturecause conflict.

Perception


81/94

p

Sensations must be converted toperceptions, the setofprocesses bywhichwe recognize, organize, and make sense ofthe sensations we receive.

Perception typically requires the integration ofsensoryinformation withinformation based upon past experience withthe world.

Remember

Perception =sensation +interpretation

When ThingsGoWrong


82/94

g g

When ThingsGoWrong


83/94

When ThingsGoWrong


84/94

When ThingsGoWrong


85/94

When ThingsGoWrong


86/94

When ThingsGoWrong (artist Julian Beever)


87/94

When ThingsGoWrong


88/94

When ThingsGoWrong


89/94

When ThingsGoWrong


90/94

When ThingsGoWrong


91/94

When ThingsGoWrong


92/94

When ThingsGoWrong


93/94

Taste


94/94

Illhav

e justa

tast

eof

this

film!

Documents

IVC Psyc 1 Fall 2010 Lecture 4 (Sensation Perception)