Visual Perception 3 Flashcards
you change your attention with you eye movements/fixation based on …
what is necesary to perform a task
the world is in constant motion, what do we do with this motion
we either move w/in the world (walk across the street) or watch the world moving (sitting by a window and watching poeple cross the street)
most or our perception is based on ____
motion
either watching (simple) or more complex (w/in a crowd that moves)
we’re very efficient at perceiving motion
what does motion help us w/
- understand events in our environment
- direct our attention to something important
- understand objects
waht does motion help us udnerstand
what is happening in our environment
ex. someone walking towards a cash register = assume they are paying for osmething
if the world was still, we wouldn’t be able to…
make sense of what’s happneing around us
another way motion helps us is for judging ___ and how _____ we are moving
direction and how fast we are moving
when we are moving, objects are moving in the opp direction relative to us. what is this called
optic flow
motion alos informs us when we need to take ____
action
ex pouring water in a glass
motion of water rising tells us when to stop pouring
what is akinetopsia
motion blindness
person unable to see things are are moving but can se ethings that are stationary
what is attentional capture
is this unconscious or conscoius
draw someones attention
ex. waving of your hands to get your friends attention
- happens consciously or unconsciously
ex. conscious when you are looking for your friend or unconsciously when your attention is directed somewhere else and you see osmething move in your peripheral vf
intentional capture is very importnat for …
survival
ex. hide and seek: a very slight movement would give away your hiding spot
- when animals detect a predator, they stay very still to avoid gaining attention of the predator
motion helps us to identify objects that are presented _______ of noise
on top of noise/ against noise
motion not only reveals ____ objects but reveals info about the objects that’s not always ___ at first
camouglaged objects
not always visible at first
there are different types of motion which all have the same perceptual effect; motion. what are they
- real motion
- apparent motion
- induced motion
- motion aftereffects
what is it called when an object moves for real
real motion
something is moving
ex. person walking down the street
what is it called when the objects do not move but appear to move bc of certain condiditons
apparent motion
what is it called when the spots seem to bounce up and down (or left and right)
first order motion
OR beta movement
changing the time interval of the alteration, the motion perception changes. if the distance btwn the 2 positions and the interval is right, we perceive…
phi movement
the perception of an object doesn’t fade straight away after the object isn’t visible but remains for a while and thereofre coincides w/ the perception of an object
waht is this called? wha tkind of motion
persistence of vision
-apparent motion
when one object moves relativ to another is called…
usually a big/small object moves relative to a big/small object. which one
induced motion
usually a big object moves relative to a small object
what is motion perception
motion aftereffect is the perception of motion after seeing a moving stimulus for a prolonged period of time
- neurons fatigue
- motion adaptation
do all these different motion phenomena have a different underlying mechanism?
we don’t really know
but there is some evidence that indicate the type of motion doesn’t play a role of how the brain perceives motion (fMRI-functional magnetic resonance imaging)
-measure oxygen: brain must be metabolically active
do stationary stimulus, real motion, and apparent motion appear to be in the same part of the brain?
stationary diff from real/apparent
what are the 3 situations of motion perceptions with examples of Dr. P
- look straight ahead while Dr. P crosses the room
- figure moves across the retinal activating diff photoreceptors on each position - look at Dr. P as he crosses the room
- figure always projected on the fovea, the figure doesn’t activate diff photoreceptors but you still perceive motion - look at screen by moving your fixation left to right
- see stationary screen even though it is moving across your retina and activating diff photorecptors each time. no motion perception
what are the 3 situations in motion perception
- look straight as object moves: object moves, eyes stationary, img on retina moves, motion perceived
- fixate on moving object: object moves, eyes move, img on retina is stationary, motion perceived
- look around screen: object stationary, eyes move, img on retina moves, NO motion perception
what are the diff appracohes on explaning motion
- info in the environment
- what’s hpapneing in environ - info on the retina/brain
- what’s happneing on the retina/neurons in the visual pathway
for information in the environment what does it take into account and not take into account? also known as?
ecological approach
doesnt care what is happening in the retina/visual system, only cares about what is happening in the environment
if you consider the downtown scene, many objects are in this scene, what does the ecological approach says this creates
an optic array
what happens in the optic array with situation 1 (look straight ahead as object moves but eyes are stationary while image on the retina moves and there is motion perception) in the ecological approach
something moving in that array relative to that environment which create local disturbances to the optical array
- the local disturbances are responsible for perceiving motion
- while Dr. P moves he makes local disturbance covering/uncovering diff parts of the stationary background
in situation 2 (fixate on moving object, object moves, eyes move, img retina stationary, motion perception) what happens to the optic array in the ecological approach
follow the moving object with your fixation but there is still disturbances happening to the optical array.
-background isnt moving so local disturbance are still produced=>enough to produce perception of motion
what happens in the optic array is sit 3? (look around the screen, object stationary, eyes move, img on retina moves, no motion perception)
whole enviroment moves as you move your eyes
- everything moves in response to your eye movements
- creates global optic flow => brain understands this so you do not appreciate motion=> everything moves at the same time
what is global optic flow
the fact that everything moves at the same time in response to your eye movement
- signals on the brain that the environemnt is stationary
- as you move across the room everything moves past you but you perceieve it as stationary bc of this
according to the ecological approach, if the whole scene is moving, what happens
there is global optic flow that signals that the environemnt is stationary
what are the 2 approaches on explaining motion based on neural processing
- reichardt detector
2. corollary discharge theory
what is the reichardt detector
a neural circuit that was proposed by wener reichardt to explain motion
-propsed that there are neurons that respond to motion in one direction and not to the other
the reichardt model can epxlain what? what does it fail to expalin
can explain first order motion (sit 1) but fails to explain more complicated phenomena (ex. why the room doesn’t seem to move when you move your eyes)
do we sense left to right motion or right to left motion
left to right motion
will actually have 2x the signal to the ganglion cell
-no inhibition of the bipolar cell
photorecptor=> bipolar cell=> ganlgion cell
to explain situations 2 and 3 of info on the retina/brain we need to not only take into account how the objects sweep across the neurons on the retina, but also…
what theory can do this?
the motion of the eyeball itself
corollary discharge theory
what are the different kinds of signals that are generated according to the corollary discharge theory
- the img displacement signal (IDS)
- the motor signal (MS)
- the corollary discharge signal (CDS)
what signal occurs when an object moves across the retina (situation 1)
the image displacement signal (IDS)
-retinal signal to the brain
what signal occurs when the brain sends a signal to the eye muscles so as to follow a moving object (sit 2)
motor signal
-signal from brain to eye
what signal occurs from the brain to the eye muscles, as well as another area on the brain for further processing
corollary discharge signal
-does not end up in the eye
the brain generates a signal that is sent to waht 2 places
eye muscles to move the eys and another location somewhere on the brain for further processing
what are the 2 signals that are transmitted to the brain
the image displacement signal and the corollary discharge signal
in situation 1 (object moves) what signal is sent to the brain
in situation 2 what signal is sent to the brain (obj followed)
1: IDS
2: CDS
if both the image displacement signal and corollary discharge singnal end up on the brain at the same time, what does our visual system do
assumes there is no motion
-this is what explains sit 3
the corollary discharge theory makes use of a mechanism or brain structure that is able to compare the signals, what is this called
comparator
how can the comparator be used
IDS => comparator => motion
CDS=> comparator => motion
IDS+CDS => comparator => no motion
where is the comparator
might not be a specific location somewhere in the brain but might be mulitple locations that act together
might also be a mechanism that processes signals w/o a specific structure
what is the importatn idea of the corollary discharge theory
that we need to take into account both the displacement of an object on the retina and the eye movements in order to explain all possible situation 1,2,3
what is the perception of no motion in sit 3
saccadic suppression
is the perception of body motion a special case?
probably
what is apparent motion
when 2 stimuli that are in slightly diff locations are presented sequentially
-depending on the rate of presenatino you might perceive motion (apparent)
the path of motion is usually the shortest possible and this is called the..
shortest path constraint
right before, during and shortly after a saccade, there is no signal leaving the retina and going to the brain (suppressing the img). our visual system can suppress a retinal image during saccadic movement, if not we how would we see an object
blurred/smeared
how soon can saccadic suppression start as soon as
as soon as 75 ms before realization of the saccade
-suggesting again that a central brain mechanism is involved in shutting down the sensory input right before, during and after and shortly after.
what are the 2 things that were learned from the fist experiemetn
- the visual system needs time to process mtion of complex stimuli (expected)
- there is osmething special when it comes to body motion
when the slow alternation condition occurred, a different part of the brain was activated, what was it
motor cortex
the brain area that deal w/ body coordiation (limb moveemnt etc)
-motor cortex judged that a motion around the head is possible (bc of the slow rate) and therefore the shortest path constraint violated
