Transcript Motion Perception

MOTION PERCEPTION
Michelle Vasquez
MOTION

Defintion: change in an object’s location over time

First order motion: change in luminance

Second order motion: contrast and texture change
MOTION CIRCUIT (SIMPLIFIED)
Barlow and Levick (1965)
D allows a delayed
response so A and B
can fire
simultaneously
 Cell X (multiplication
cell) fires if both B
and D fire
simultaneously,
passing the message
on to the motion
detector cell, M

MOTION CIRCUIT (LESS SIMPLIFIED)

Here is a less simplified version of our motion
circuit:
White: object we see
Blue: object’s path of
motion
Red: delay cells
Purple: multiplication
cells
Green: motion
detector
EDGES OF RETINA

The edges of our retina are sensitive only to
movement
No color or object identification
 When the movement stops, the object becomes
invisible


Example: waving hand around the side of your visual field
RETINA

The retina is stimulated by the moving of images

Image-retina movement


“on-off” receptors respond when a change in illumination
occurs
Movement coded as neural signals in the retina, or in the
visual projection areas of the brain
 Image runs across the retina sequentially fires receptors
in its path
 The faster the image travels, the greater the velocity
signal this will give
MIDDLE TEMPORAL LOBE

The middle temporal lobe is also known as MT or
V5

External motion  primary visual cortex  middle
temporal lobe

Most neurons here are selective for motion in one direction
and do not show much sensitivity for color or form
EYE-HEAD MOVEMENT

Eye following moving objects

The fact that the eye is being moved is signaled to the
brain and used to indicate movements of external
objects

It seems easy to detect if movement is due to our own
motion among surrounding objects or due to their
movement if we are moving (if our legs are moving)

But what if you are in a car? The only source of info
is from our eyes. (Keep this in mind when we talk
about motion paradox.)
WHAT IS MOVING?

Saccade suppression: reduction of visual
sensitivity that occurs when one makes a
saccadic eye movement

Eliminates smear from retinal image motion during
eye movement
o

Saccade and smooth pursuit work together so there is no
sudden displacement of objects in front of you
Comparator: area of visual system that receives
one copy of the order issued by the motor system
when the eye moves (the other copy goes to the
eye muscles)

Compensates for image changes caused by eye
movement
EYE MOVEMENTS


The superior colliculus is responsible for
initiating and guiding eye movements
3 types:
Smooth pursuit: type of eye movement in which the
eyes move smoothly to follow an object
 Vergence: the two eyes move in opposite directions
 Saccade: rapid movement of the eyes that changes
fixation from one location to another (also seen in
REM sleep)

EXAMPLE

Moving your eyeball with your finger, no signal
sent from eye muscle to comparator, therefore
visual input visual input interpreted as shaking
world
WHAT DO WE USE MOTION PERCEPTION
FOR?

Navigation


We want to determine what is moving and what is
stationary to be able to navigate around
Identifying objects

“biological motion”- pattern of movement of living
beings (humans and animals)


We want to identify moving objects and their actions
Avoiding collision

Ration of retinal image size at any movement to the
rate at which the image is expanding
BIOLOGICAL MOVEMENT

http://www.lifesci.sussex.ac.uk/home/George_Mat
her/Motion/
ILLUSIONS OF MOTION

Waterfall effect

We already know that cells respond to motion
in one particular direction

Motion after affect
 After viewing motion in a constant direction for a
sustained amount of time (15 seconds or so), we see
stationary objects moving in the opposite direction

http://www.lifesci.sussex.ac.uk/home/George_Mather/Mot
ion/
APPARENT MOTION

The impression of smooth motion resulting from
the rapid alteration of objects that appear in
different locations in rapid succession

http://www.lifesci.sussex.ac.uk/home/George_Mather/
Motion/
MOTION PARADOX (PARALLAX)

When we move (ex: to the right), near objects
move against our motion (to the left) and further
objects seem to move with us (to the right)

Ex: the moon when driving in a car

The moon is so distant that its angular position does
not change, yet it appears to be not so far away

Therefore, we ‘assume’ it is moving with the car
SUMMARY
Motion information helps us determine where
objects are going and when they are likely to get
there
 There is a motion detection circuit that uses both
delay and sum information
 The middle temporal lobe is involved in
perception of motion
 Eye movement v. object movement is
distinguished by the suppression of motion
signals generated by eye movements so
everything is not ‘smeared’

CREDITS



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Sensation & Perception by Jeremy Wolfe and others. (Sinauer,
2006)
Eye and Brain by Richard Gregory. (Princeton University Press,
1997)
The Student's Guide to Cognitive Neuroscience by Jamie
Ward. (Psychology Press, 2006)
“Introduction to Motion Perception”
http://www.lifesci.sussex.ac.uk/home/George_Mather/Motion/
(George Mather, 2008)
"Perception (psychology)" http://encarta.msn.com © (Microsoft
Encarta, 1997-2009)
“Motion Perception, Elementary Mechanisms”
http://wexler.free.fr/library/files/burr%20(0)%20motion%20perceptio
n,%20elementary%20mechanisms.pdf (David C. Burr, 2003)
“Motion Perception”
http://vision.rutgers.edu/klab/research/motionPerception.htm (Tom
Albright, Richard van Wezel, Karen Dobkins, Amy Rezec, 2008)
“Sensation and Perception”
http://www.sinauer.com/wolfe/chap7/startF.htm (Sinauer, 2006)
THANKS FOR YOUR ATTENTION
The end!