Motion Flashcards
What is motion
Spatiotemporal event
Change in position over time (the time part is important)
Why is movement perception essential
Essential for visually guided actions and interactions with environment
Give ex of movement perception
Camouflaged animals easier to spot when moving
Allows brain to separate moving objects from static surroundings
What should movement perception require
Logically speaking = should only require ability to perceive successive still frames
But irl = fluid
What is akinetopsia
Loss of movement perception
Rare neuropsychological disorder in which the affect individual has no perception of motion
Can be caused by lesions to area mt/mst = middle temporal gyrus
= see streams of multiple frozen images trailing in wake of moving objects, like flashing strobe, if noting in motion and held himself straight = normal vision but if anything moved = leaves stream of static copies - cannot drive, walk, very bad
Kinda looks like nude descending staircase
What is apparent motion
Perceived motion
Illusory impression of smooth motion resulting form rapid alternation of objects that appear in diff locations in rapid succession
(Like Cartoon movies - play frames and will perceive as smooth)
Describe apparent motion graph
Position over time - combos of this
Perceived motion - too fast = v large dots and move fast = see 2 dots flickering
Perceive motion - too slow = distance small and duration long, to induce apparent motion
Describe motion detectors circuit = problem and solution
Reichardt detectors
= M neuron registers change in position between a and b but = would still respond if 2 cars or if car moving backwards
So solution = add neuron d = incorporates delay
Describe motion detectors circuit = exactly
Have in area v1 of brain
Delay = predetermined
Ex = A—D B (all go to m) - M will only fire if d and b come to m together = tells you its moving = created rightward motion tuned neuron
Leftward motion tuned neuron = if delay in b neuron
What is movement after effect
Due to habituation
Describe simple and complex cells in area v1
Motion detectors
- recall previous vision lectures
Describe aperture problem
Fact that when a moving object is viewed through aperture - or receptive field = direction of motion of a local feature of part of an object may be ambiguous
= limited visual field in our motion detector circuits - do not know full motion, if going down or up or right or left if only see through aperture
Describe correspondence problem
Problem faced by detection system of knowing which feature of frame 2 corresponds with which feature in frame 1
Describe relationship between aperture and correspondence problems
Closely related
Have aperture problem bc of correspondence problem - bc do not know how to match same feature across 2 time frames
What can solve the corespondance problem - determine global motion
Motion info from several local apertures or receptive fields can be combined to determine the global motion of the object
Describe whole process of determining global motion
Several directions of motion within each aperture are compatible with stimulation receptor is receiving
Only one is possible motion in all apertures = true global motion of object
Identify only correct motion for all of them (to match frame 1 and 2)
Describe eye movements generally
Eyes constantly move
Bc acuity - need to move eyes but don’t perceive world as moving
Have to scan environment
Describe smooth pursuit
Voluntary eye movement in which eyes move to smoothly follow a moving object - track object
Describe saccade
Type of rapid eye moment - made both voluntarily and involuntarily
Eyes rapidly change fixation from one object or location to another - 3-4 times per sec
Conscious and unconscious
Describe vergence
Type of eye movement
Both voluntary and involuntary
2 eyes move in opposite directions
Describe the 2 vergence movements
Convergent eye movements turn the eyes inwards
Divergent eye movements turn the eyes outwards
Describe reflexive eye movements
Automatic and involuntary eye movements
Describe reflexive eye movements - ex
When eyes move to compensate for head and body meovemnt while marinating fixation on particular target
Nervous system calculates movements of head and compensates for it
Describe microsaccades - define
Reflexive
Involuntary small jerk like eye movement
Describe microsaccades - what is function
Prevent visual fading
Allows us to see behind blood vessel in eye
Improve visibility of sharp details
Compensate for sudden loss of acuity a few mins outside of fovea
Describe ex of eye movements - proving seeing is not passive
Look at point, put finger on start and move it while looking at point then repeat but follow finger with eyes (smooth pursuit) = fixation point doesn’t seem to move
But displacement on retin is the same - perceive finger to be in motion in first case but perceive fixation poring to be stationary in second case
But both items move to left across retinas
= BECASUE in second case there was an eye movement, when move eyes = visual system stops encoding info do no see world as moving too = saccadic suppression
What is Saccadic suppression
Temporary reduction of visual sensitivity that occurs during rapid eye movements - saccades to prevent motion blur and maintin visual stability = only for voluntary
Describe ex of exp involving microsaccades
Exp where guy paralyzed his eye muscles = preventing microsaccades
Experienced also the complete visual fading = always blind
Wanted to move eye but couldn’t so experienced movement in opposite direction of where he intended to move eyes = succadic surpession - tells visual system before move
In this exp = visual system expected to move as intended but didn’t = weird effec
What is visual fading
Focus on point in middle of blurry colourful image
Turns grey
= bc prevents eyes from scanning and it’s hard to remember by heart where each colour is so visual system forgets there is colour
Describe optical illusion
Pattern - illusion with many diff aspects
Seems lik it’s rotating but not
When saccade = see movement
Effect works on cars too
