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Chapter 7

Chapter 7 textbook notes


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
7

Page:
of 5
Chapter 7: Motion Perception
Motion aftereffect (MAE): Illusion of motion in a stationary object. Occurs due to the
prolonged exposure to moving objects.
oOpponent processes for motion detection
Computation of Visual Motion
oCell A, Cell B, Cell D, Cell X, Cell M
oWerner Reichardts model (bugs in receptive field)
Apparent motion: illusory impression of smooth motion. Results from rapid change
between objects that appear in diff places in rapid succession.
oSigmund Exners spark light experiment in 1875
Appears in As receptive field, disappears, reappears in Bs receptive
field short time later
Appeared movement
The correspondence and aperture problems
oAperture: small opening which allows only a partial view of the object.
oCorrespondence problem (motion) : Problem faced by motion detection system
of knowing which feature in frame 2 corresponds to a particular feature in
frame 1
oAperture problem: direction of motion unclear when viewed through a
aperture
oBroader implications:
v1 cells see the world through a small aperture (grey triangles)
global motion detector (orange triangle) solution
another set of neurons listen to the v1 neurons and integrate
the conflicting signals
Detection of Global Motion in Area MT (middle temporal lobe in the cortex)
www.notesolution.com
oLesions to magnocellular layers of LGN (lateral geniculate nucleus) impair
perception of large fast moving objects
oInfo from magnocellular neurons v1 MT
oMajority of neurons selective for
motion in one particular direction
oLittle sensitivity for form and
colour though
oNewsome & Pare (monkeys & dots )
Identify overall direction of correlated motion
To detect direction a neuron must integrate info from many local
motion detectors
Monkeys fully trained could recognize the correlated motion when only
2-3% of dots were moving in this direction.
Lesioned monkeys MT areas (then needed 10xs # of correlated dots to
correctly identify direction of motion)
Monkeys ability to discriminate stationary patterns =
unimpaired.
Performance improved , however, few weeks after lesion
(learned to use o/ brain areas)
oAnother experiment: looked for groups of neurons that responded to 1
particular direction. (showed new stimuli & electrically stimulated identified
MT neurons)
Monkeys pointed for motion in preferred direction even though dots
were moving in opposite direction
Strong case that MT= site for general motion detection neurons in the
visual system
Motion aftereffects (revisited)
Stationary object: neurons tuned to diff directions of motion normally balanced
(neurons sensitive to upward motion fire at the same rate as neurons sensitive to
downward motion. Therefore, signals cancel out & no motion is perceived.
www.notesolution.com
BUT, when we look at a waterfall too long, the detectors sensitive to downward
motion become fatigued & when we look at a rock (for ex) the neurons sensitive to
upward motion fire faster than the tired downward sensitive neurons. Thus perceive
the rocks as drifting up.
Interocular transfer: the transfer of an effect (such as adaption) from one eye to the
other.
oInput from both eyes is not combined until cortical area V1, where neurons
show a preference for input from one eye or another but respond to some
extent to stimuli in both eyes
oMAE in humans is caused by the same brain region shown to be responsible
for global-motion detection in monkeys: cortical area MT
oDirection-selective adaption...fMRI, MAE due to a population imbalance in
area MT
First-order motion: the motion of an object that is defined by changes in lamination
oLuminance-defined object: an object that is delineated by changes in reflected
light
Second-order motion: the motion of an object that is defined by changes in contrast
or texture
oTexture-defines (contrast-defined) object: an object that is defined by changes
in contrast or texture, but not by luminance
Nothing moves in Second order motion( just like in first order)
oNothing to move in 2nd order
oOnly thing that changes is strips of dots are inverted from one frame to
another
o2nd order proves that matching discrete objects across movie frames is not
necessary for motion perception
oSpecialized mechanisms for 2nd order (distinct from mechanism used for 1st
order)
o2nd order MAE transfers even more completely b/w eyes than 1st order
www.notesolution.com