PSYCH 2220 Sensation and Perception I Lecture 6

PSYCH 2220Sensation 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

sustained cells

magnocellular layers of LGN

parvocellular layers of LGN

DORSAL

VENTRAL

SPATIAL VISION

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.

Just low spatial frequencies….

… all spatial frequencies

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

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

visible

invisible

Spatial Frequency

Th

resh

old

co

ntr

ast

CONTRAST SENSITIVITY FUNCTION

Co

ntr

ast

sen

siti

vity

low

high

high

low

Low spatial frequency High

Hig

h

con

tras

t

Lo

wTHECONTRASTSENSITIVITYFUNCTION

Low spatial frequency High

Hig

h

con

tras

t

Lo

w

stationary

moving

.. which revises…

Big rfs best for low sf found in periphery

Where cells prefer MOVEMENT

(on way to dorsal stream good for action…)

DEPTH PERCEPTION

Artist’s cues

StereopsisParallaxPerspectiveSizeOverlayTexture gradientAccommodation and convergence

Cues to DEPTH

DavidHockney

The Ame’s room as

conflict between

SIZE and PERSPECTIVE

Ame’s room movie

perspectivevs

size

The IMPOSSIBLE TRIANGLE as

conflict between

PERSPECTIVE and OVERLAY (or OCCLUSSION)

The playing card illusion

as conflict

between overlay and size

ab

6

A

Perspective and overlay cues

overlay > perspective

perspective > size

overlay > size

6

A

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 Law2 – Moon Illusion

EMMERT’s LAWIf retinal image stays the same

then perceived size will depend on distance

small thing close

big thing far

holding the screen closermakes the after imagelook smaller

holding the screen furtheraway makes the afterimage look bigger

EMMERT’s LAWIf retinal image stays the same

then perceived size will depend on distance

DEMO ONLY!! They have been MADE different sizes here!!)

CRITICAL POINT: the moon always has the same visual angle, but different perceived distance.

Scale demo (from Lord of the Rings)

Binocular disparities

and stereopsis

left eye's viewof a cube

right eye's view ofthe same cube

(red over left eye)

The correspondence problem:

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

Floating Square

a

b

c

d

ca

b

adot b is seen only bythe left eye

dot 'c' is seen only bythe right eye

dot 'a' is seen by botheyes

left eye

right eyeRIGHT EYE

LEFT EYE

(red over left eye)

Reversing the glasses opposes

stereopsis and artist’s cues

Necker cube

Cube

Pyramid (lots of depth)

(red over right eye)

Checkerboard

AUTOSTEREOGRAM

Ame’s Window Demonstration

overlay > perspective

perspective > size

overlay > size

overlay > stereopsis

stereopsis > perspective

…but only at close distances

6

A

Pulfrich illusion

a b

left eye right eyeab

dark glass toadapt (and slowdown) the righteye

c

Parallax

parallax video

Accommodation and convergence

Accommodation and convergence

need someone who hasn’t got

stereopsisparallax

doesn’t know about

artist’s cues:(perspective, overlay, texture gradients,size)

who could this be???

Accommodation cues can be used tosolve the visual cliff.

Neural basis of stereopsis

Ocular dominance bands

fb

a

left eye

right eye

1 2 3

RIGHT EYE

LEFT EYE

FAR

NEAR

FAR CELL

fb

a

left eye

right eye

1 2 3

RIGHT EYE

LEFT EYE

FAR

NEAR

NEAR CELL

NEAR FAR

left eye

right eye

some cells will respond tomovement in the direction ofthe filled arrows, but not inthe direction of the openarrows.

… motion in depth leads us nicelyinto….

VISUAL MOTION

My motherby

David Hockney

The scrabble game by David Hockney

Visual motion

Active motion of real image

INFLOW OUTFLOW DATA

Passive motion of real image

Active motion of after image

Attempt to move paralyzed eye

Passive motion of after image

No movement

No movement

PREDICTIONS

No movement

YES movement

YES movement

YES movement

YES movement

No movement

EXPERIMENTS

No movement

YES movement

Active motion of real image

INFLOW OUTFLOW DATA

Passive motion of real image

Active motion of after image

Attempt to move paralyzed eye

Passive motion of after image

No movement

No movement

PREDICTIONS

No movement

YES movement

YES movement

YES movement

YES movement

No movement

EXPERIMENTS

No movement

YES movement

No movement

YES movement

YES movement

No movement

YES movement