Post on 14-Nov-2015
description
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