Biases: An Example Non-accidental properties: Properties that appear in an image that are very...

Biases: An Example

Non-accidental properties: Properties that appear in an imagethat are very unlikely to have been produced by chance, andtherefore are likely to reflect properties of the 3-D world.

straight lines parallel lines

view-point invariant properties

mental representation of objects

view-point invariantcat

book

tree

key

etc..

mental representation of bars of light view-point dependent

?



book

tree

key

etc..


1) Direct models



book

tree

key

etc..


1) Direct models:

Lades et al Model

Poggio & Edelman Model

•Input layer like representation in V1 (called “Gabor Jets”)•Inputs on that layer are matched to inputs in a memory layer•The object is identified based on the match with least distortion

•Input layer like representation in V1•3-layer network is trained to rotate all views of an image to one view.•The hidden units are seen as a way of rotating images to match memory images (“radial basis functions”)



book

tree

key

etc..


mental representation of non-accidental

properties of an image

view-point invariant

2) View-point invariant

Lowe’s SCERPO Model

Ullman’s Model

•Input layer takes information represented as it is in V1•view-point invarient information is extracted•this allows the input image to be rotated in order to fit an image stored in memory

The problem with all of these theories:

The representation of objects in memory is stored asa two-dimensional image, which visual images are rotated, distorted, and matched to.

But in actuality, objects are three dimensional thingsin the world.

So lets make a model which has the basic units thatmake up mental representations of objects beingthree-dimensional solids, rather than lines and edges.



book

tree

key

etc..





mental representation of geons


Geonsstraight, parallel

curved, parallel

Y intersections

Y intersections

corner



book

tree

key

etc..







what processing

rectangle unitcylinder unit

cone unittube unit



book

briefcase

key

etc..



where processing

above unitbelow unitleft of unit

righ of unittemporal binding

Evidence for geons?

Experiment 1: Visual Priming

(response)

time

(response)

Reaction Time: 900 ms.

Evidence for geons?


time

(response)


(response)

Evidence For Geons: Priming StudiesFirst Second

Shared?Lines Geons Basic Response TimeEdges Cat.

Yes Yes Yes Yes

No Yes Yes Yes

No No No No

700 ms

700 ms

900 ms

Evidence For Geons: Priming StudiesShared?

Lines Geons Spec. Basic Resp. TimeEdges Cat. Cat.

Yes Yes Yes Yes Yes

No No Yes Yes Yes

No No No Yes Yes

700 ms

800 ms

800 ms

First Second

Objects, Faces and Rotation:Objects

900

920

940

960

980

1000

1020

0 60 120 180 240 300

Face Recognition

Recognizing faces is an entirely different problem(computationally) from recognizing objects?

Objects

Faces

• “M” shaped function

• Shape of rotation function?

Face Recognition Experiment

Objects, Faces and Rotation:Faces

900

920

940

960

980

1000

1020

1040

1060

0 60 120 180 240 300

Face Recognition

Recognizing faces is an entirely different problem(computationally) from recognizing objects?

Objects Faces

• “M” shaped function• Less affected by illumination

Recognition by components(Geon Theory)

• Shape of rotation function?• More affected by illumination

Recognition by coordinates(Templates)

different processes?

Double Dissociation

Patient Studies

• Prosopagnosia: Objects can be recognized, Faces can not.

Processes responsible for object recognition:

Processes responsible for face recognition:

Double Dissociation

Patient Studies

• Prosopagnosia: Objects can be recognized, Faces can not.• (Patient CK): Faces can be recognized, Objects can not

Processes responsible for object recognition:

Processes responsible for face recognition:

Double Dissociation

Patient Studies

• Prosopagnosia: Objects can be recognized, Faces can not.• (Patient CK): Faces can be recognized, Objects can not

Neuroimaging Studies

• Faces activate the FFA area of the temporal lobe• Objects activate the PPA area of the temporal lobe

Double Dissociation

General Form

IF:The ability to perform some task X is affected by or correlatedwith some factor A (damage to an area, activity in a part of the brain, or performing some other task) but not factor B (damageto a different area, activity in a different part, or some other task),AND:The ability to perform some task Y is affected by or correlatedwith some factor B but not factor A,THEN:There is a double dissociation between X and Y, and themechanisms required to perform them are functionally independent.

DissociationWhat and Where Pathways

Some patients

Can identify objects by shape

CannotSay where objects areCannot navigate the world

DamageParietal lobeDorsal visual stream

X

DissociationWhat and Where Pathways

X

Some patients

Cannot identify objects by shape

CanSay where objects areCannot navigate the world

DamageTemporal lobeVentral visual stream

DissociationWhat and Where PathwaysPatient D.F.

Cannot Explicitly line up a line with a lineTask: Take an envelope and line it up with this

lineCan

Use motor system (part of “where” pathway)to do same task just failed atTask: Take this envelope and “mail the letter” pretending that this line is a mailbox

• Recognize faces normal way “ Hey I know you”

• Recognize by change in skin conductance for familiar faces

DissociationTwo face recognition systems

• Person A can recognize normal way but no change in skin conductance

• Person B cannot recognize in normal way but does have change in skin conductance

DissociationTwo face recognition systems

Biases: An Example Non-accidental properties: Properties that appear in an image that are very...

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