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PSYCH 2220 Sensation and Perception I Lecture 6. Keywords for lecture 5. Dorsal/ventral streams, action/perception streams. Grandmother cell hypothesis. Face cells, hand cells (in ventral stream), prosopagnosia. Distributed processing. transient cells. DORSAL. magnocellular layers of LGN.

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PSYCH 2220

Sensation and Perception I

Lecture 6

slide2

Keywords for lecture 5

Dorsal/ventral streams, action/perception streams. Grandmother cell hypothesis. Face cells, hand cells (in ventral stream), prosopagnosia. Distributed processing.

transient cells

DORSAL

magnocellular layers of LGN

parvocellular layers of LGN

VENTRAL

sustained cells

slide4

FOURIER’S THEOREM:

“any complex curve can be mathematically described as the sum of a series of sine waves”

Variation of luminance across a scene can therefore be described as a series of sinewaves of different SPATIAL FREQUENCIES.

slide7

High spatial frequencies here are NOT telling you about the face but about the annoying squares….

slide8

…when the squares are too small to be seen, then the remaining information (i.e., the face) can be seen clearly.

slide9

high

low

invisible

Contrast sensitivity

Threshold contrast

visible

low

high

Spatial Frequency

CONTRAST SENSITIVITY FUNCTION

slide10

THE

CONTRAST

SENSITIVITY

FUNCTION

High contrast Low

Low spatial frequency High

slide11

moving

stationary

High contrast Low

Low spatial frequency High

slide12

.. which revises…

Big rfs best for low sf  found in periphery

Where cells prefer MOVEMENT

(on way to dorsal stream good for action…)

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Cues to DEPTH

Stereopsis

Parallax

Perspective

Size

Overlay

Texture gradient

Accommodation and convergence

Artist’s cues

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David

Hockney

slide18

The Ame’s room as

conflict between

SIZE and PERSPECTIVE

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The IMPOSSIBLE TRIANGLE as

conflict between

PERSPECTIVE and OVERLAY (or OCCLUSSION)

slide27

The playing card illusion

as conflict

between overlay and size

slide35

perspective > size

overlay > perspective

overlay > size

slide36

Size constancy:

a given object seems the same size as its retinal image size varies with distance from the viewer.

Mechanisms of size constancy can be clarified by looking at when it breaks down…

1 – Emmert’s Law

2 – Moon Illusion

slide37

big thing

far

small thing

close

EMMERT’s LAW

If retinal image stays the same

then perceived size will depend on distance

slide38

EMMERT’s LAW

If retinal image stays the same

then perceived size will depend on distance

slide43

Binocular disparities

and stereopsis

slide48

The correspondence problem:

How does the brain know which dots in the right eye go with which dots in the left eye?

slide50

RIGHT EYE

LEFT EYE

slide52

Reversing the glasses opposes

stereopsis and artist’s cues

slide57

Pyramid (lots of depth)

(red over right eye)

slide62

perspective > size

overlay > perspective

overlay > size

overlay > stereopsis

stereopsis > perspective

…but only at close distances

slide69

Accommodation and convergence

need someone who hasn’t got

stereopsis

parallax

doesn’t know about

artist’s cues:

(perspective, overlay, texture gradients,size)

who could this be???

slide70

Accommodation cues can be used to

solve the visual cliff.

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FAR CELL

RIGHT EYE

FAR

NEAR

LEFT EYE

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NEAR CELL

RIGHT EYE

FAR

NEAR

LEFT EYE

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FAR

NEAR

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My mother

by

David Hockney

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PREDICTIONS

EXPERIMENTS

OUTFLOW

DATA

INFLOW

No

movement

No

movement

Active motion of real image

No

movement

YES

movement

Passive motion of real image

YES

movement

YES

movement

Active motion of after image

Passive motion of after image

YES

movement

No

movement

No

movement

YES

movement

Attempt to move paralyzed eye

slide84

PREDICTIONS

EXPERIMENTS

OUTFLOW

DATA

INFLOW

No

movement

No

movement

Active motion of real image

No

movement

YES

movement

Passive motion of real image

YES

movement

YES

movement

Active motion of after image

Passive motion of after image

YES

movement

No

movement

No

movement

YES

movement

Attempt to move paralyzed eye

No

movement

YES

movement

YES

movement

No

movement

YES

movement