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 cellssustained cellsmagnocellular layers of LGNparvocellular layers of LGNDORSALVENTRAL

SPATIAL VISION

FOURIERS 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.

visibleinvisibleSpatial FrequencyThreshold contrastCONTRAST SENSITIVITY FUNCTIONContrast sensitivitylowhighhighlow

Low spatial frequency HighHigh contrast LowTHECONTRASTSENSITIVITYFUNCTION

Low spatial frequency HighHigh contrast Lowstationarymoving

.. 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

Artists cuesStereopsisParallaxPerspectiveSizeOverlayTexture gradientAccommodation and convergenceCues to DEPTH

DavidHockney

The Ames room as

conflict between

SIZE and PERSPECTIVE

Ames room movie

perspectivevssize

The IMPOSSIBLE TRIANGLE as

conflict between

PERSPECTIVE and OVERLAY (or OCCLUSSION)

The playing card illusion

as conflict

between overlay and size

Perspective and overlay cues

overlay > perspectiveperspective > size overlay > size

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 Emmerts Law2 Moon Illusion

EMMERTs LAWIf retinal image stays the samethen perceived size will depend on distancesmall thing closebig thing far

EMMERTs LAWIf retinal image stays the samethen 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

(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

RIGHT EYELEFT EYE

(red over left eye)

Reversing the glasses opposes

stereopsis and artists cues

Necker cube

Cube

Pyramid (lots of depth)(red over right eye)

Checkerboard

AUTOSTEREOGRAM

Ames Window Demonstration

overlay > perspectiveperspective > size overlay > size overlay > stereopsisstereopsis > perspectivebut only at close distances

Pulfrich illusion

Parallax

parallax video

Accommodation and convergence

Accommodation and convergence

need someone who hasnt got

stereopsisparallax

doesnt know about

artists 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

RIGHT EYELEFT EYEFARNEARFAR CELL

RIGHT EYELEFT EYEFARNEARNEAR CELL

NEARFAR

motion in depth leads us nicelyinto.

VISUAL MOTION

My motherbyDavid Hockney

The scrabble game by David Hockney

Visual motion

Active motion of real imageINFLOWOUTFLOWDATAPassive motion of real imageActive motion of after imageAttempt to move paralyzed eyePassive motion of after imageNo movementNo movementPREDICTIONSNo movementYES movementYES movementYES movementYES movementNo movementEXPERIMENTSNo movementYES movement

No movementYES movementYES movementNo movementYES movement