psych 2220 sensation and perception i lecture 6. keywords for lecture 5 dorsal/ventral streams,...
TRANSCRIPT
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