Psyc230 lecture slides_firsthalfofcourse

We behave effectively with respect to the world. What makes that possible?

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23

4

Problem: the world is at some remove. How do we achieve action at a distance?

We behave effectively with respect to the world. What makes that possible?

What are the mechanisms that allow perceptual agents to achieve action at a

distance?

PhenomenaWhat kinds of properties of the world are perceived?

PhilosophyWhat kinds of properties and theoretical assumptions should

anchor our theory of perception?

PhysicsWhat kinds of properties are present or “recorded” in the

energy media of the world?

PhysiologyWhat kinds of properties can sense organs and nerve cells

“record” and how doe these sense organs influence the perception?

What do we have to understand to understand the mechanisms of perception?

PhenomenaWhat kinds of properties

are perceived?

Problem: the world is at some remove. How do we achieve action at a distance?

Themes from the Overview

We behave effectively with respect to the world. What makes that possible?

PhilosophyWhat kinds of

properties/assumptions should anchor our theory?

PhysicsWhat kinds of properties

are present or “recorded” in the energy media?

PhysiologyWhat kinds of properties

can sense organs and nerve cells “record”?

Ancient notions… (500 B.C. to 1000 A.D.)•eyes receive facsimiles of objects

Indirect RealismWe know the world through

intermediaries

eye is a chamber that captures images

…persist in modern view•copies stand between us and the worldeye as camera•disconnected sensations get connected higher up

•light rays hit eye as pointillistic mosaic

The image is ambiguous, impoverished. (1) It doesn’t match the world.(2) It doesn’t match our experience.

Environment Organism link is bad therefore…

Perception requires processes to elaborate input, constructing a series of representations of the world that increasingly come to resemble it.

Examine the E O link

A B C DA B C D

How good are the images?

Molyneux’s Premise (1692): distance is not perceivable by eye

What gets linked?

What do you need to fix the bad link? Experience Knowledge:Empiricism

An object in the world at some distance from me that goads me or stimulates me to act:

distal stimulus or SD

The pattern at a sense organ caused by an energy pattern in the world:

proximal stimulus or SP

3 Old Guys who set the conceptual agenda

1. Berkeley (1700s)

Eventually, visual image memories of motions idea of distance.

touch is the rationalizer•direct contact with the world•not susceptible to the loss of structure•can help out those senses that are susceptiblemuscular feelings can help fix defects in visual image once I learn which images co-occur with which feelings.

extended arm grasps bottlecontract arm— image expands

45˚90˚

worries about physiology & its psychological counterpart

2. Müller (1826)

Sensory receptors•Are stimulated by energy (light, sound, pressure)•But not mere conductors of those properties

Emphasizes the contribution of anatomy & physiology

ELECTRIC PULSE

PRESSURE CHEMICALS

Visual sensation

OPTIC

NERVE

LIGHT

Eye designed to capture

light

SOUND

AUDITORY

NERVES

Auditory sensation

Ear designed to capture

sound

Müller’s Theory of Specific Nerve Energies impose their own characteristics— “specific nerve energies”—on the mind. This, not the physical properties themselves, is why the qualities for the different senses are different.

SP must be interpreted re: what is normal

•What would normally have produced these features?•What goes with what?

3. Helmholtz (1821-1894): THE MAJOR FIGURE

SD SP

object patchwork of sensations

Helmholtz’s Theory of Unconscious Inference

SP is converted to sensations—a mental response to energy (direct)

Sensations that habitually occur together become linked through memory—associations.

Normalcy is embodied in internal algorithms or rules.

cues + rules = Unconscious Inference

The input is a disjointed, inadequate copy of the world.Perception works by improving the copy via rules.

Perception of the world is indirect.

Attended Stimulus

Environmental Stimulus

Action

Stimulus on the receptors

Transduction

Processing

Perception

Recognition

The Perceptual Process:

Stimulus

Perception

Stimulus Energy

Sensation

Physiological sensation

Perception

Three key relationships

Knowledge cues & rules

Unconscious Inference

Berkeley: coupling of percepts uses meaningfulness of one to explain another

Müller: the sensory apparatus itself contributes its character to the input

Helmholtz: mental computations reflect internalized knowledge of the world and how it affects us.

The nature of E S influences the nature of S P

World Energy Sensations Perception

All share the theory of inadequate input

ignored link

historically important links

currency is converted into currency: How does physical energy map onto psychological

experience? Measurement is the key to making perceptual psychology a science

The nature of E S influences the nature of S P

World Energy Sensations Perception

ignored link

historically important links

currency is converted into currency: How does physical energy map onto psychological

experience? Measurement is the key to making perceptual psychology a science

Energy Sensation Experience

Energy SensationE S

Physical Psychological

Perceive event (cat rubbing leg)

Event in world

Pressure (energy)

Sense properties of pressure () e.g. amount, location.

Pressure sensitive nerves

Energy SensationPsychophysics

Anticipated by Weber (mid-late 1800s)If the amount of energy is too small, it’s not

noticeable.

Psychophysics looks at the E S link

Say “now” when you see the gray square.

Absolute threshold

minimum energy that can just be detected

Trial 1 Trial 2

No

No

No

No

No

No

Yes

Trial 5

No

No

No

No

Yes

Trial 3

No

No

No

No

No

Yes

Trial 4

No

YesYesYes

Trial 6

YesYesYesYesYesYes

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

Intensity (I)

3

4

5

6

7

8

9

10

2

1

11

12

0

654

1

32

Trial

Smallest Intensity Detected

657

6

75

Absolute threshold

Mean 6

6

Determining the Absolute threshold: Method of Limits

Anticipated by Weber (mid-late 1800s)If change in amount of energy is too small, it’s not

noticeable.

Psychophysics looks at the E S link

Weber’s focus was on discriminating two detectable stimuli: How similar could they be and still be sensed as

different?

Not absolute change but relative change

Just Noticeable Difference

I / I = K

A change in intensity

relative to the initial intensity equals a constant.

– =

Just Noticeable Difference (JND)

Different

I2 I1

102 g 100 g

I2 - I1 = I

I: physical intensity

Different

I2 I1

101 g 100 g

Same

I sensed is not absolute!!

Rather, the JND is a constant threshold.

Difference Thresholds: How similar can objects be and still be sensed as different?

Consider what happens when we use different values of intensity (I)

100 + 2 = 102 2/100 = 1/50 (.02)

200 + 4 = 204 4/200 = 1/50 (.02)

400 + 8 = 408 8/400 = 1/50 (.02)

The greater the value of I the greater must be the value of I for a difference to be sensed.

WEBER’S LAW: = K (a constant)II

Intensity I

JND I + I

II

Change in II K

JND’s for all senses: - Vision (e.g. change in brightness) - Hearing (e.g. change in loudness)

I

I

I

I

I = 20

The correspondence between a physical stimulus and our perception of it is systematic

but it is not always 1:1.

I = 500I = 500

.2

.5

smaller K more sensitive lower threshold

K = 1 I = 20

I = 1000I = 500 K

= .5

I = 20I = 10

1Slope

I / I = K 1st truly quantitative law of psychology

Fechner (mid-late 1800s)

Weber’s goal was to study jnds; Fechner’s insight was that such a quantification allows you to probe mental states.

Fechner (mid-late 1800s)

Demonstrated how mental activity could be measured quantitatively!!

… also started to examine whether we can assume a

equivalence of changes in intensity of stimulation?

Steven’s attempted to understand the relationships between and intensity in his examination of Magnitude estimation.

0 1000 2000 3000

Stimulus Intensity

300

200

100

10

Standard = 100

Response = 160

Response = 130

Response = 200

Response = 25

Response = 50

T1

T2

T3

T4

T5

300

200

100

100 1000 2000

3000Stimulus Intensity

Response = 150

Response = 225

Response = 350

Response = 90

Response = 95

T1

T2

T3

T4

T5

Standard = 100

Subjective intensity of magnitide () is some constant multiplied by the intensity (I) to some

power (n).

Stimulus Intensity

Mag

nit

ud

e

Esti

mate

Log Stimulus Intensity

Log

M

ag

nit

ud

e

Esti

mate

= kIn

n = the slope of the line in the log-log plot

Perceptual Sense reflects Power Law Functions

Implicit Metatheory: To say there is a absolute or noticeable threshold is to say

that there are un-noticeable things.

To say there is a just noticeable difference is to say that there are also un-noticeable differences.

To say the perception is power law like is to say that the…

Connection between mind & body is in the quantitative relation between mental sensation & material stimulus

I/I = k and = kIn highlight slippage between & (not 1:1).

How do you measure the change in stimulation?

You need methods…

…that yield quantities that can be put into law form

Fechner formally developed Psychophysics as the methodology,

a methodology that endorses a metatheory

Assumes the some currency has some currency

May not be 1:1, but we must therefore understand:

Understanding these things might help in understanding the processes of

perception.

Lets start with vision…

Psychophysics looks at the E S link

1. The physics of different energy medium,2. How the physiology is designed to transduce this energy

and… 3. How his transduction maps onto sensory and psychological

experience?

currency is converted into currency: How does physical energy map onto psychological

experience?

World Energy Sensations Perception

Understanding these things might help in understanding the processes of

perception.

Lets start with vision…

Assumes the some currency has some currencyMay not be 1:1, but we must therefore understand:

Psychophysics looks at the E S link

1. The physics of different energy medium,2. How the physiology is designed to transduce this energy

and… 3. How this transduction maps onto sensory and psychological

experience?

Light: The stimulus for vision

Electromagnetic radiation structured in waves* over space

distance

en

erg

y amplitude = Intensity

Wavelength

same amplitudedifferent

wavelengths

multiple wavelength

s(vs. pure)

same wavelengthdifferent amplitude

Complexity or Purity

Different wavelength

shue

multiple of wavelength

saturationbrightness

Differentintensities

Amplitude ≈ Intensity

Wavelength

Wavelength: most relevant for color vision…

How is light structured?

Light travels far•we can know about far

objects

surfaces, substances

source

Some light gets to eye

Light travels fast•we can know them

immediately

reflected scattered absorbed

Light travels straight•good for image-

production

Why light? Vision as a distance sense

The eye captures light reflected from objects and forms an image on the back of

the eye.

How “should” the image be formed?

box with a pinhole as the

eye

Solution #1:

Allow one ray from each part of the object into the eye.

Camera Obscura (Alhazen)

Limitation: Doesn’t let in much light—blurry image

Problem: Spatial ordering of rays reflected from the object have to be recovered from the divergent light.

Allows larger holemore lightsharper image

Limitation: Clear focus depends on the power of the lens and angle of divergence of light rays.

Problem: Spatial ordering of rays reflected from the object have to be recovered from the divergent light.

…while letting in enough light for a clear image.

Solution #2: Use a lens that refracts light so that rays

from the same point on the object converge.

Limitation: Clear focus depends on the power of the lens and angle of divergence of light rays.

Problem: Spatial ordering of rays reflected from the object have to be recovered from the divergent light

…while letting in enough light for a clear image.

Solution #2:Use a lens that refracts light so that rays

from the same point on the object converge.

Different distance of object from eye changes angle of light rays Out of focus for

that lens.

…of objects at varying distances.

Solution #3:

Lens with variable optical power changes shape to accom- modate the distance of the object to the size of the eye.

Problem: Spatial ordering of rays reflected from the object have to be recovered from the divergent light

…while letting in enough light for a clear image

The eye as a chamber for capturing light

Optical parts

Structures for gathering and focusing light

cornea

iris

lens

pupil optic nerve

What properties should the eye have?

Translating parts

Structures for copying light and sending

signals

fovea

Light is focused on light-sensitive photoreceptors of retina that convert or transduce physical energy into neural activity

•Lens shape can be changed to accommodate to the distance of an object for focusing on the back of the eye—the retina—centering on the fovea•Fluid in eye keeps its shape from changing so that focusing properties are reliable

Focusing-relevant features highlight the importance of the retinal image

LVF RVF

Retinal Image is Starting Point for Vision…and we have two

Visual Fields defined relative to fixation x:

Right Visual Cortex

LVF projects to right side of each eye and on to the Right Hemisphere

LVF RVF

Retinal Image is Starting Point for Vision…and we have two

Visual Fields defined relative to fixation x:

RVF projects to left side of each eye and on to the Left Hemisphere

Right Visual Cortex

Left Visual CortexRegions of left eye correspond to regions of right eye

At some point we have to (re)connect visual fields.

LVF projects to right side of each eye and on to the Right Hemisphere

•Philosophy: Begin with objective physical properties•Physics: Intensity, wavelength of reflected light•Physiology: Brightness, color but not 1:1•Phenomena: Product of mental computation

Physics Psycho- Anatomy & Algorithms physics Physiology

Goals: Get copy of world inside headDifficulty: Pointillisitic nature of light (and

sensations)

Solution & Problem: Eyes capture images

world energy sensations pattern perception

Pervasive Themes

Before we had techniques to see cells, we had behavioral data:

Go from bright light into dark room—can’t see at first

Improves for 5 min., levels off… improves again for 15–20 min.

thre

shold

minutes in dark•1st acts fast, adapts less.Kink in function is clue 2 functions•2nd adapts slowly but more.

2 functions 2 types of photoreceptors 2 job descriptions:

Transducing the image

•work in dim and bright light•provide sensitivity and clarity•work in B&W and Color

Location, number, connections differ.

Rods •across periphery

•fovea only has cones

no. of receptors per square mm

Blindspot: no receptors because the optic nerve leaves the eye.

•many:1 connections •1:1 connections

•more plentiful120,000,000

•fewer in number8,000,000

What are consequences?

What are consequences?

So does shape: rods

and cones

Cones

•many:1 with later cells

•1:1 with later cells

Ø!Ø

ØØ

minutes in dark

Threshold(minimal

visible light intensity)

Return to dark adaptation curves for hints

very little light required

more light required

Differ in Sensitivity

2 weak signals that are separate remain below threshold of next cell

less sensitive

2 weak signals that are connected can exceed threshold of next cell

more sensitive

Ø

Ø

ganglia ganglia

How a pattern is experienced depends on where it projects on the retina

Is there a cost to pooling signals?Is there a benefit to keeping signals

separate?

detail is missed: less acuity

detail is noticed: greater acuity

•mosaic of receptors breaks up continuity of world

Array of ≈ 130,000,000 photoreceptors converts the retinal image into a neural image to be transmitted to the brain.

But…

How good is mapping between world and experience?

Which of these problems get fixed higher up? How are they fixed?

•image is upside down

•different parts of retina have different sensitivities

•mosaic of receptors breaks up continuity of world

Array of ≈ 130,000,000 photoreceptors converts the retinal image into a neural image to be transmitted to the brain.

But…

Receptors outnumber cells in the next layer pooling of information, editing, altering before signals are passed along

How good is mapping between world and experience?

Which of these problems get fixed higher up? How are they fixed?

mechanismsrules

•image is upside down

•different parts of retina have different sensitivities

Ganglia respond to receptors, not to light (register differences in light)

Examine the language of ganglia: action

potentials

All or None

Cells beyond receptors condense and reorganize data130,000,000 receptors 1,000,000 ganglia

• many, many rods : 1 ganglion; 1 (or a few) cones : 1 ganglion a lot of editing What kind?

What kind of stimulus does a ganglion prefer?

Use single cell recording with electrodes

oscilloscope

amplifier

•a still eye to keep stimulus where you want it.•stimulate various areas of the retina see effect on a particular ganglion.

microelectrode

time (sec)

volt

ag

e

reveals editing

Without stimulus there is a base level of spontaneous activity.

Task: Find the region on the retina whose stimulation will change the resting level (higher or lower) of Ganglion “A”.

How: Scan retina with stimulus to see where ganglion’s activity is affected (where matters)

Homogeneous gray spontaneous activity.

Spot of light greater than spontaneous activity

Dark spot in area less than spontaneous activity

Within area greater than spontaneous activityOutside area less than spontaneous activity

Spontaneous firing rate is affected up or down

concentric ON/OFF regions Ganglion cell’s receptive

field(a collection of retinal cells)

“ON” response “OFF” response

Distribution of concentric ON/OFF regions arises from connections among preganglion collectors

What happens with light outside the ON/OFF region?

spontaneous rate

excited rate

inhibited rate

spontaneous rate

What is experienced depends on where it hits retinaAssessing various ganglia yields a receptive field map

overlap, producing a mosaic covering the whole retina

(also OFF center/ON surround cells)

How does Center/Surround organization work?

patch of light over entire field

patch of dark over entire

field

Uniform illumination on region modest activity

•ON center “prefers” light; surrounding OFF circle “prefers” dark

Increased activation from ON center countered by decreased activation from OFF surround.

antagonistic responses from center and surround

lateral inhibition

Decreased activation from ON center countered by increased activation from OFF

surround.

Dark edges over OFF surround with light on ON centervigorous response: whole receptive field is getting its preferred stimulusdetects and accents light/dark boundary

Edges are preferred by this kind of cell.

illuminate only the center

dark bar on the surround

What pattern on the retina would be preferred by a Center/Surround cell?

Consequences of antagonistic relationship between center and surround

Intensity of Center

Response

Intensity of Center

Response

Intensity of Center

Response

same response to dif. intensities

dif. responses to the same intensity

Constancy Illusions

Good mapping in a limited range?

From what we know about acuity, how should size vary in different areas of the

retina?large in periphery; small near fovea

Many:1 vs. 1:1—Receptive fields vary in size

Physiological mechanisms are recovering edge and size information building blocks of meaning.

Small receptive fields respond best to small objects; large to large beginning of object size extraction.

From what we know about preferences of receptive fields, how should they respond to objects of different sizes?

Acuity: smallest high contrast detail perceived at a given distance

Receptive fields have consequences for the kinds of patterns that go into Unconscious

Inferences.

What letter is this? F E A H O D P R Identification Acuity

Can you see this? Detection Acuity

1 or 2? Pattern or gray?

Resolution Acuity

K

Note disparities between and

made possible by lateral inhibition — mechanism that highlights edges through sideways connections

among cells.

Illusory consequences illustrate how it works.

dependence on “irrelevant” conditions (e.g., distance)

The “private line” from foveal cones to the brain provides fine detail……but it’s neurologically expensive receptive field organization is important

Mach bands—regions of heightened and reduced brightnesses.

Intensity changes in stepwise fashionLight

Intensity

1 2 3 4 5 6Position

high

low

Light Intensity

100

40

a b c d e f g h

activity w/NO neighbor: 40 40 40 40 100 100 100 100Inhibition from Left: -2 -4 -4 -4 -4 -10 -10 -10Inhibition from Right: -4 -4 -4 -10 -10 -10 -10 -18Total Output: 34 32 32 26 86 80 80 72

Perceived

Lightness

lightness does not.

Receptors

(activity - inhibition)

Mach bands do not exist physicallywouldn’t be picked up by a photometerPhysiology imposes its character on the input•A physical contrast—a border—that does exist is accentuated•Machinery can be inferred from experience

stimuli ≠ perception of those stimuli

Lightness Contrast

Implies interaction in connections between neighboring cells:some signals boosted, some signals reduced

: Central squares reflect same amount of light.: The darker the surround, the lighter they look.: Central squares reflect same amount of light.

B

A

B

AALEFT looks darker than ARIGHT

Initial “strength” of signals (registered by rods)

ALEFT = ARIGHTBLEFT > BRIGHT•excitatory or inhibitory

Signal from BLEFT inhibits signal from ALEFT lateral inhibition

If signal from B exceeds threshold of laterally connecting cells, signal from A will be reduced

Signal from BRIGHT does not affect ARIGHT Consequently, ALEFT < ARIGHT

•sideways

Subsequent connections•end-to-end

•ganglia pool information, change from what is given copies (which are inadequate)

Evidence for assumptions of Indirect Realism

•separate receptors, connected into receptive fields disconnected sensations, mosaic•eye as camera, receptors as film image language

Same mechanism is destructive and constructive

•It distorts relative to Illusions•It enhances the detection of an important feature of the world edges

sends excitatory signal when stimulated

sends inhibitory signal when stimulated

front view

•many:1 with later cellsgreater sensitivity

•1:1 or few:1 with later cellsgreater acuity

side view

Receptive fields care about size & shape…

…but not orientation.

”

reduced rate:stimulus hits both excitatory and inhibitory cells

Orientation influences what objects mean

Pool some more.

To overcome mosaic, connect receptive fields.

Receptive fields overlap

Across a collection of receptive fields, orientation matters

Collection reports to cells in the cortex.

They have receptive fields too

Record from 3 cortical cells

Cortical cells do edge detection but more cleverly

Cortical receptive field shapes are not uniform Hubel & Wiesel (1959, 1962; Nobel Prize 1981)

stimuli must be positioned appropriately

maximal response to stimuli of a particular orientation ±15°.

response

rate

response

rate

Simple cellsreceptive fields look like their preferred orientations

Complex and

Hypercomplex cells

Some cells prefer movement of those features in a particular direction

•don’t care about precise placement•larger receptive fields•no clear ON-OFF regions•prefer moving stimulus•combinations of features

Measure activity in cell that prefers downward moving horizontal 3 cm line

Provide some information about where, what, and what’s it doing.

Are Cortical Cells Feature Detectors?

Rate of firing is the only vocabulary—how is ambiguity resolved?

Reduced response if orientation or size or motion is not exactwhich is it?

More complex response is still ambiguous

directi

o

n

orientation

response rate

Response is ambiguous•Respond maximally, not exclusively, to their feature

responserate ambiguity at level of single cell

• Multiple representations (> 100,000,000 cortical cells) of the retina and visual field

• Each cortical area performs different processing tasks, extracting specific feature

• Integrated with other properties • Hierarchical organization of visual system geared for building up

ever-better representations of world: simple to complex

Activity of cell ensemble reduces ambiguity in coding

•What kinds of images does the eye produce? which qualitative properties are preserved, lost, distorted

Physical Psychologicallight or an object detection thresholdsdifferences in intensity, etc. jnds, acuityIntensity, reflectance constancy, contrastdifferent wavelengths not distinguished in dim lightX-ray, infrared visible spectrum

gives us variables builds from elements

meaningless adds meaning

Strategies of Indirect Realism

•Psychophysics Characterize match to the world quantitatively

Reality question is emphasized in color perception.•Objects have no color. Reflected light is no more colored than are radio waves! •To appear colored, reflected light must be picked up by the right kind of eye and nervous system.

Color is a psychological thing.

Visual stimuli are built hierarchically from simple to complex

Which level is real, the simple end of the hierarchy or the complex end? The variables or the experiences?

The first representation—levels of contrast—is meaningless and must be reconstituted to get more specific and more meaningful.

Is an edge real?

surfacepigmentshadow

wavelengths, not colors

produce; reflect, absorb; transmit

Color is totally subjective

•Light rays, paints, filters, etc. merely use radiant energy selectively.

•Color is a product of the visual system, not the visible spectrum.

how our retinal physiology responds

White light decomposed into spectral components refracted by a prism and split into rays of different wavelengths. amount of refraction determined by wavelength

Newton (with some refinements)

Nonetheless, color sensations are related in consistent and measurable ways to physical

features of light

infrared (not visible)redorangeyellowgreenbluevioletultraviolet (not visible)

Complexity or Purity

Different wavelengt

hshue

multiple of wavelength

saturationbrightnes

s

Differentintensities

Amplitude ≈ Intensity

Wavelength

How do we respond to different kinds of light?

Pure #1 + Pure #2 = Composite

equivalence is due to nervous system •Different things with identical neural effects: metamers

pure vs. composite light

If Pure #1 + Pure #2 + … = White then 1 & 2 are complementary

Components “cancel” or “blend” psychologically but not physically spectral components would still be detectable

to instruments.

Both are white

: wavelength : hue

You can add pure colors and get one that’s not a spectral color no characteristic wavelength

530

650

600O

Metamers tell us how to organize the optics: Complementary colors are opposites in some

sense

580580

R

G

B

YY

460

???P

490 B-G

GG--YY490490

A color circle, but…

Other experiences suggest organizations more elaborate than a circle

: intensity : brightness

What happens when there is more or less light?

blue . . . heather blue . . . graygreen . . . heather green . . .grayred . . . pink . . . gray

What does the color look like?

The higher the %white the less saturated a color will look.The higher the % other wavelengths, the less saturated a color will

look.: spectral purity :

saturation Maximal at moderate intensities only

bri

ghtn

ess

white

black

Colors on opposite sides gray

Broadest portion appears at medium lightness.

Any cross-section color wheel for a particular lightness

Wavelength + Intensity + Purity Color experience

all colors can be obtained from a few primaries

tells us about the physiology of color perception

The Color Solid

Phenomenological observations: •the color solid, metamers, complementary

colors allow inferences about physiology

A single wavelength is matched by different amounts of 3 primaries

indicate limits of the information senses pick up indicate how the brain uses that information

Metameric Matching:

Present a target color and have observer match it with a mix of others.

Would 1 cone type work? Or 1 cone per color?

3 primaries

ComparisonxR + yG + zB

1 wavelength

Test FieldC =

Young: 3 specialized cones each acts as a channel responsive to specific spectral composition.

Retina as mosaic of independent triads of cones

Light at each retinal point analyzed into 3 components

Return to experience: •Why is there no reddish-green?•Why is color blindness a matter of confusions? most common is red with green•color afterimages show same combinations

S M L100

0

400 500 600

Wavelength

% of Max. Absorptio

n

Young-Helmholtz (and Newton and Maxwell) Tri-chromatic Theory

Helmholtz: 3 types of cones, each with a graded sensitivity function

What is the origin of the pairings?

Color blindness comes in pairs

Trichromatic theory not the whole story

Color afterimages

complementary colors:

R-G & B-Y

Color blindness comes in pairs

Trichromatic theory not the whole story

Color afterimages

Opponent Process Theory: Perhaps outputs of cones are re-coded somewhere into pairs whose members are antagonists (Hurvich & Jameson, 20th Century)

YYB R

G YYB R G

Opponent Organization

•Hue determined by relative activity of R-G and B-Y;

• lightness determined by activity of B-W cells; •saturation by which kinds of cells are most

active:

violet

• Complementary colors cannot coexist because a pair cannot respond actively to both

• Color deficiencies are characterized by pairs

light

optic nerve

fovea

retina

DESIGN OF RETINA

TO OPTIC NERVE

To Brai

n

RODS

CONES

BIPOLARS

GANGLIONS

LIGHTLIGHT

A NEURAL SYSTEM OF OPPONENT PROCESSES

+

––

CONES

GANGLION

IF + > –, THEN “BLUE”IF – > +, THEN “YELLOW”

IF + > –, THEN “RED”IF – > +, THEN “GREEN”

CONES

GANGLION

–

+ +

FOR BOTH OPPONENT PROCESS SYSTEMS:

IF + = –, THEN “GRAY”

(ACHROMATIC)

Wavelength info at retinal level; feed into opponencyFits into the overall theme of the perceptual system missing physical detail, restoring lost structure, making things up as it goes along. But it is also an example of the visual system getting what it needs: There is a biological advantage to seeing color.

Note: We’ve really been limited to sensations. Perception is still to

come.

Color coding is a two-stage process.

Puzzle:

All this happens inside eyes and brain. How do we experience the world as outside?

101

Bananas?3 pointy cone shapes?

Edges are a specialty of the visual system.Specialty implicates a mechanism for perceiving separable objects.

•Neurophysiology: primitives hierarchical combos

Old theories illustrate persistent issues

analytic introspection: specialized technique for observation stimulus error: mistaking the object for experience

Sensations vs. Perceptions

Structuralism was a kind of mental chemistry. Elemental structures combine to build perception

What does the visual system start with? What are the elements?What do you really see, without interpretation?

No, reallyNo, reallyNo, reallyangled planes, ellipse?black lines, yellow patches

Important historically because of •its strategy atomistic & anatomistic•reaction against it

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How do I know that this pattern is a hand?

•“geons” •and their relationships•applied to SP & to stored representationStructural Description

Examples of types of representations and types of computations

Analysis must provide components abstract enough to match stored representation.

More candidate primitives

Or this? Or this?

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corner of front surface Keep track of vertex-connected surfaces eliminate those that are inconsistent

not always

3-D corner of one objectnot always

For complicated—natural—scenes, occlusion is a problem

Even if these are identified as cylinders, how do we know they are part of the same object?

We need rules about what’s likely.

…with what you know about objects

Given experience, assign to SP the SD that is most likely to have caused it.

Overcomes problem caused by occlusion

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=

Different neural activity = different forms… HOWEVER… Form (object) recognition still presupposes a solution…an internal representation.

Still doesn’t answer the how question. How (where) does perception occur?

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A cross … But why? Perception is not simple addition of elements •“Crossness” not derived from adding circles•Defects (e.g., gaps) in RI would be preserved in brain

Structuralism ignored interactions in nervous system play organizing role

The Gestaltists

Why do things appear as they do?

What do you see?

Gestalt is German for whole form“The whole is different from the sum of its parts.”

Principles of Organization encourage grouping, segregation form emerges

Yes! But what are they?

i. They are what they are?

iii. The brain processes are what they are?

ii. SP are what they are?

is 9 circles

1 SP 2 experiences

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Grouping or organization is not in the stimulus.

Seen as 3 pairs of lines•SP does not dictate that over

Seen as intersecting shapes•SP does not favor

The Law of Proximity does

or

Seen as alternating columns•SP does not dictate that over

The Law of Similarity does

or

The Law of Good Continuation does

over

Seen as triangle in front of 3 circles•SP does not dictate that over

The Law of Closure does

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What counts as a form or grouping distinct from a background?

3-D or 2-D?

In general, Simplicity

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What is the figure can be complicated

Ambiguous Figures: For same SD and same SP, two percepts are possible

How can you have 2 simultaneous, incompatible representations of the same thing?

•Figure-ground is reversible•Can be shifted by attention

Figure vs. Ground: What does the edge belong to?

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Of the alternatives allowed by the proximal stimulus… infer the more likely.

Figure vs. Ground: What does the edge belong to?

The Helmholtzian Solution:

Use knowledge of which configurations are likely: Principle of maximum likelihood.Make Unconscious Inferences about the world.

Contrast detection is not enough identify which form the edge belongs to(Pattern recognition presupposes a solution)

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Structuralists emphasized identifying primitives as adding or associating sensations…theirs were too subjective, too qualitative

Gestaltists emphasized emergent properties or organizing through grouping lawstheirs were descriptive, not predictable.

But, how it looks ≠ what it is.Form requires further processing.

Teacher through your glasses?

Teacher in your locket?

far

near

For example, distance matters

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Pattern recognition = ƒ(distance, size, shape)

Is there reasonably reliable structure that might be used to solve Molyneux’s problem? A B C

D

How do we know both relative distance and absolute distance?

Back to Helmholtz and Unconscious Inference

How does SP come to indicate a particular SD given that SP is2-dimensional and, therefore, ambiguous?

Reasonably reliable in a Helmholtzian what-is-normal sense is provided by cues

RI for large, far objects = RI for small, near objects

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•texture gradient

•interposition

•SP was probably caused by a particular SD

•Become associated with properties of SD through experience.

II. Attempts to simulate depth: pictorial cues

•relative size

Aspect of SP

I. Berkeley “on-line”: oculomotor cues

X

X

convergence

accommodation

X

X

Distance Perception

•linear perspective

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III. 2 eyes that receive slightly different views: binocular disparity

Left thumb behind,Right thumb in front;Both far away

Thumbs close together

R

Amount of disparity indicates relative distance, separation

RL

Thumbs far apart

LL

Both up close

RL R

Motion Based Cue for Depth:

Ever look out the window while riding in a car?

Direction of Travel

Objects in the foreground move by faster than objects in the background - Very distant objects appear to remain stationary

Motion Parallax

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Size Perception

But there’s ambiguity…

RIpumpkin = RIapple Which is bigger?

RIpumpkin > RIapple pumpkin is larger than apple

I. Retinal Image Size: Larger objects project larger RI

II. Familiar Size pumpkins are larger than apples…

•except for small pumpkins compare to similar objects in the scene: III. Relative Size

Unconscious Inference uses knowledge about what’s normal

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Knowledge is needed to make sense of ambiguous cues to attribute the proper cause to your SP.

Helmholtz’s Unconscious Inference

In natural scenes cues co-occur strengthen the impression of depth & size.

In experiments, cues are manipulated alter the impression of depth & size.

Strategy: isolate cues or put them in conflict to assess

•cues’ relative potency•illusions gain insight into normal processes, algorithms

We perceive constant object properties despite variability in the SP that is our contact with them. Perceptual Constancies

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SizePerceived = ƒ(RI Size, DistancePerceived)

Tested by Holway & Boring (1941)

2 hallways:•target disk on L

Indicate size by method of adjustment

Targets chosen to project same RI @ every distance

Percept-Percept Coupling

•response on R

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Manipulate available cues to distance and assess effect on perceived size:

•fewer cues to distancemore reliance on RI

Breakdown of Size Constancy

F

M

S

P

Actual Size

Perceived Size

constancy

slope = 1

retinal size

slope = 0

Full Cue

Monocular

Static

Peephole

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Helmholtz

•SP is bad ( shows it)•Perception good (experience shows it)•fixed by rules (experiments show it) Perception is indirect

SP1 ≠ SP2

Percept @ d1 = Percept @ d2

Size Constancy

d1

d2

Ex. I. Perceived Size is unaffected by distance

Perceptual Constancies

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Rule: RI size decreases with D. So…•If A & B project same size SP•And if A is farther than BA must be bigger than B

percept-percept coupling

A looks bigger than B

A

B A = B

Cue: SP:A = SP:BCue: linear perspective

says “A is farther than B”

Perc’d size is derived from perc’d distance

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SP1 ≠ SP2

Percept @ p1 = Percept @ p2

Shape Constancy

p1

p2

Ex. II. Perceived Shape is unaffected by perspective

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Appearance is affected by interpretation!

Parallelograms look similar in size and shape(one is rotation of other)

ShapePerc’d is derived from distancePerc’d

Adding distance cues changes inferred shape.percept-percept coupling

Manipulate depth cues & assess consequences for ShapePerc’d.

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Fixing SP is logically prior to pattern recognition. What form is it?

Fundamental problem is normalization of image for memory.

Compare to stored representations•How abstract can the representations be? •How tolerant are matching processes?

How would a representational account handle movement?

Objects in the world often move…they are not not static!!

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125

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Motion Perception

t2

t3

t1

Physical Event

Perception

Apparent (Stroboscopic) Movement

Do we see things as they are because of the proximal stimulus? No

Do we see things as they are because of brain states? Yes

Or…

A temporal property (change over time) is derived from a succession of static retinal images.

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Interpret with respect to likelihoods.

Apparent motion of the disk induced by assumption that enclosures don’t move.

The same assumption would underlie our experience of non-illusory motion, too.

Again, illustrated by an illusion: “induced motion”

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1

23

4 1 4

23

BUT…

Helmholtzian account: compare RI with commands to muscles Did I tell myself to move?•ambiguity if I’m being moved

passively•ambiguity if we’re both moving

Stimulation of successive retinal locations motion

1

23

4

Same pattern for car moving to left and me moving to right.

1

23

4

Puzzle: How is leftward movement of something distinguished from rightward movement of me (or my eyes)?

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t1

Form Perception Motion Perception

Sequence of static RI infer motion•xyz at t1 vs xyz at t2 vs xyz at t3•deduce rotation about Y

How do you know which points correspond if you don’t already know the type of motion?

t2t3

Helmholtz asked “what is likely?”

What if both are likely?

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Shortest-Path Constraint… simplicity again!!!

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Themes from the Overview

•Phenomena: What kinds of properties are perceived?•Physics: What kinds of properties are “recorded” in the energy media?•Physiology: What kinds of properties can sense organs and nerve cells “record”?•Philosophy: What kinds of properties should anchor our theory?

We behave effectively with respect to the world. What makes that possible?

WHAT WHO HOW

The Phenomena of ATTENTION: Orienting

What is the girl feeling…emotion?What is the information for making these judgments?

• Attention drawn to most informative aspects of picture.

Eye Movements

The Phenomena of ATTENTION:

8 8

8 8

8 8

s c

z k

e t

8 8

8 8

8 8

s k

z c

ft

e

s c

z k

e t

s k

z c

ft

e

8 8

8 8

8 8

Stimulus Driven Attention

Search for the letter ‘c’

The Phenomena of ATTENTION:

Goal Directed – Intentional/Change Blindness

Does the number of white T-shirt players change?

Any Gorillas???????

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Movie

The Phenomena of ATTENTION:

Selective ListeningDICHOTIC LISTENING

WHAT IS KNOWN ABOUT UNATTENDED?Only physical characteristics (speech like sounds). Not meaning.

I cannot tell a lieNever kill a snake

SHADOWING

I cannot tell a lie

“unattended” “attended”

COCKTAIL PARTY EFFECT

Except when important or relevant (e.g. name)

The ever present Unconscious at work yet again….

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Proximal Stimulus

MeaninglessSensations

Association/CuesDistal Stimulus

Incomplete“Percepts”

Incomplete“Percepts” Perception

Unconscious Inferences, information processing, Laws of organization

Indirect Perspective of Perception Assumes:

Both relinquish the responsibility of perception to an “internal”, “mental”, knower… a homunculus… who organizes and isolates cues and compares percepts and representations.