Download Slides from Lecture 11/17/2004 (Andy Clark)

Sensation
&
Perception
Motion Vision I:
Basic Motion Vision
Why care?
•Most animals have some form of
motion vision (vs. Color)
•A large part of the brain is devoted to
motion processing in these animals
Motion processing in the brain
Why motion?
Motion as a rich source of
survival-relevant information :
• Ecologically relevant information
• Breaks camouflage
• Heading perception, time to collision
• Image segmentation, figure/ground
• Object perception, structure from motion
• Depth perception
• Attention guidance
Some
demonstrations...
Motion = Change of
position over time?
Motion as a separate
perceptual dimension
•The motion aftereffect (MAE)
•Apparent motion
•Motion illusions, induced movement
How hard can it be?
Challenges
•Relation between movement of
luminance on retina and object
movement in world is weak.
•Apparent motion, flicker,
correspondence problem
•Image segmentation
Basic principles
•Reichardt detectors in V1
integrate luminance signals
from the LGN.
Retina  LGN  V1
Reichardt detector
Hz
LGN
cells
(input)
V1 response
*
1
*
2
*
t
X
V1 cell
(integrator)
*
3
4
5
6
t
Review: Orientation
tuning in V1
•V1 neurons have orientation preferences.
•These can be understood by analyzing the
receptive field properties of the respective
cell.
Review: Orientation
tuning in V1
y
Hz
-
+ x
y
Hz
-
+ x
y
Hz
-
+ x
Space-time plots
x
x
t
x
t
t
•Motion as orientation/tilt in space-time
Motion as a tilt in space-time
t
t
-
-
+ -
+ -
x
t
x
t
-
-
+ x
+ x
•V1 neurons tuned for orientation in space time  Extracting
motion information by Direction, speed selectivity.
•So computationally, motion
detection is essentially the same as
edge detection. The RFs are just
oriented in different dimensions.
•How to construct a space-time
receptive field?
Constructing the Space-Time RF
A B
C
D
E
Delay
decreases
from A to E
x
t
Hz
X (A, B, C, D, E)
t
Summary
•Motion perception is very common
among animals. It´s evolutionary
survival value is high.
•Motion detection is an inference
made by the brain about the dynamics
of objects in the world
Summary
•The perception of motion is a
fundamental perceptual quality. It is
not derived from other qualities.
•Motion extraction in V1 can be
understood by the concepts of
Reichardt detectors and Orientation
tuning in space-time.
There is much more...
Multi-step model of
motion perception
1: Local measurement of motion
information (direction, speed), esp. V1
2: Constrained integration of local
motion information (particularly in MT)
3: Utilizing motion information for
action guidance (e.g. MST, FEF, etc.)
Higher upward:
•Perception of biological motion
•Perception of structure from motion
•Perception of heading (optic flow),
taking eye movements into account, etc.