motion perception Flashcards
types of motion (4)
real motion, induced motion, motion aftereffect, apparent motion
induced motion (what & example)
stationary object appears to move cause nearby object is moving (e.g. pigeon head moves forward, body catches up, looks like head moving backwards)
motion aftereffect
prolonged viewing of moving pattern causes stationary patterns to appear to move in the opposite direction (e.g. waterfall illusion, spiral illusion)
explanation for motion aftereffect
-due to fatigue of direction-selective motion detectors
-detectors respond best to 1 direction
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detectors that prefer leftwards motion will respond ___ to stimulus that moves leftwards; detectors that prefer rightwards motion will respond ___ to stimulus that moves leftwards; perceived motion to the __
strongly; a little; left
apparent motion
created by flashing 2 or more stimuli successively with the appropriate temporal delay and spatial separation (e.g. tv)
interstimulus interval (ISI)
time between frame 1 offset and frame 2 onset
what variables affect apparent motion?
interstimulus intervals & separations (how much time & how far apart?)
Reichardt detector
specific form of neural motion detector circuit that combines signals initiated at slightly different times from adjacent retinal locations
delay neuron
allows signals from neurons 1 & 2 to reach multiplication cell at same time
Reichardt detectors respond to what motions?
apparent motion (as long as time and space are right) & real motion
does rightward Reichardt detector respond to leftward motion?
no
aliasing
is retinal image motion is sampled at a lower rate than the object speed, motion may appear to be in opposite direction (e.g. wagonwheel effect)
wagon wheel effect: with wheel rotating clockwise, at slow speed, wheel appears to be rotating ___ & ____ at fast speed
clockwise; counterclockwise
motion correspondence problem
which feature in frame/time 2 corresponds to a particular feature in frame/time 1 (e.g. wagon wheel effect)
with motion correspondence problem, what is our usual perception?
the shortest, simplest path
motion correspondence problem with moving train illusion
2 equally good solutions (train leaving or arriving) so it is ambiguous
aperture problem
when moving object viewed through an aperture, direction of local motion may be ambiguous (e.g. circle with diagonal lines); brain does not correctly solve the correspondence problem
local motion
motion of parts of a pattern and/or over a small region of the retina
global motion
motion of the full pattern involving a much larger region of the retina
global motion detector and local motion detectors circuit
global motion detector integrates signals from 4 local motion detectors to solve the aperture problem; combining all the signals might solve motion correspondence problem
neurons tuned to direction of motion first found in
V1
why no motion detectors in retina? (photoreceptors, retinal ganglion)
-individual photoreceptors can signal presence/absence of car, but not its direction of motion
-retinal ganglion cells (& LGN neurons) have circular receptive fields & don’t respond selectively to motion direction
V1 neurons are sensitive to (and what do their receptive fields look like)
motion, and most are selective for direction; long receptive field
why are V1 neurons susceptible to the aperture problem?
cuz V1 neurons are direction selective with small receptive fields which makes them able to detect local motion
neural basis of motion aftereffect in V1
direction-selective neurons in V1 (cat) reduce their firing rate after a few seconds of exposure to stimuli moving in their preferred direction; neural fatigue; recovery takes longer following a longer adaptation period
MT (V5 and sometimes MST) and its neurons
motion processing; almost all neurons in MT respond to motion; most are direction selective
hMT+
MT and MST (as opposed to monkey brains)
MT lesion produced what in monkeys that V4 lesion did not?
deficits in detecting patch of moving dots (motion detection)
V1 vs MT+ activation by moving & stationary dots
V1 almost equally by both dots; hMT+ more by moving dots than stationary or blank field
neural basis of motion aftereffect in hMT+
human cortical areas, especially hMT+ show direction-selective adaptation; reduced response to adapted direction relative to mixed directions in hMT+ but not V4v (direction-selective imbalance)
direction-selective imbalance
reduced response to adapted direction relative to mixed directions in hMT+ but not V4v; just difference between adapted neurons vs non-adapted neurons (e.g. motion aftereffect test of pattern moving inwards then outwards)
sum of evidence that MT important for motion perception
monkey lesion studies, human fMRI, motion aftereffect (human fMRI)
MT neurons are (selective of __ and fields)
direction selective with large receptive fields
range of apparent motion stimuli in human black threshold curve
psychophysics; below threshold: motion perceived; not perceived above
t/f: good agreement between psychophysicsal apparent motion perception and neuron responses, particularly in MT (range of apparent motion stimuli in human graph)
true
MT neurons respond to ____ spatial separations than V1 neurons which is an important property for
larger; local motion integration
when all dots moving in the same direction; coherence is; half?; 2/10 dots in same direction?
100%; 50%; 20%
motion coherence threshold
% of dots that must move together for global direction to be discriminated
effect of MT lesion in monkey on global dot motion coherence
global dot motion coherence threshold increases from 3% to 100% (needs all dots moving together to discriminate global direction)
effect of hMT lesion in patient on global dot motion coherence vs control
coherence threshold 2-5% for control; 100% for patient (needs all dots moving together to discriminate global direction)
microstimulation
electric current passed through electrode to activate cortical neurons
microstimulation applied to column of direction-selective MT neurons with similar preferred direction had what effect on monkeys?
biased monkey’s responses in favour of direction preferred by stimulated neurons (e.g. global leftward motion seemed to move rightward when rightward selective neurons stimulated)
plaid pattern
when 2 gratings moving in different directions are superimposed, perceive moving plaid pattern; fused when see plaid; type of global motion requiring integration of local motion signals
___ of MT neurons respond to plaid direction not component directions
1/3
sum of evidence that MT neurons are global motion detectors
-single-cell evidence (apparent motion response at larger spatial separations, microstimulation, plaid instead of component)
-lesion evidence (elevated motion coherence thresholds)
first order stimuli & examples
contain shapes defined by luminance differences between shape and background (2-dot apparent motion, global dot motion, plaid motion)
second order stimuli & examples
contain shapes defined by variations in texture or contrast with no luminance difference (series of moving bars ‘multiplied’ by pattern of stationary random dots; pixels being reversed; reversal in contrast)
would second order stimuli activate Reichardt detector?
no because there is no change in luminance
real world example of second order motion
camouflaged animals
evidence for specialized mechanisms for 2nd order motion
double dissociation between 1st and 2nd
2nd order motion proves matching objects across movie frames is not necessary for _____
motion perception
third order motion & involves what
attentive tracking of moving features (figure vs ground) involves hMT+, V3A, parietal cortex
single object tracking is evidence for
third order motion (attention required to see the motion) (tracking the dot)
attention-generated apparent motion
perceived direction of motion depends on which colour you pay attention to
