22. movement Flashcards
4 reasons movement is important?
- you can see things you wouldn’t otherwise see
- high sensitivity to biological motion
- motion onset attracts attention
- animate motion also attracts attention
3 ways movement lets you see things you wouldn’t otherwise see?
1a. kinetic depth effect (structure from motion)
–> reveals 3D shape
1b. random dot kinematogram (hidden object)
1c. gradual/fuzzy contours disappear without retinal motion
Kinetic depth effect def? AKA? Explain, example?
- “structure from motion”
- Motion reveals a 3D shape that you couldn’t previously see bc there were no/little other depth cues in the scene
- Ex. on youtube –> black image contour on white background, didn’t look like anything until it started to rotate and you could see what it was
Random dot kinematogram meaning?
- an image of random dots with no defined shape in it
- a portion of the dots in a specific shape move, and you can identify the shape (ex. square)
- ex. in book was a fish blending into the sand, but you see it when it moves
Gradual contours disappear without retinal motion meaning? What didn’t it apply to?
- focus on a single spot in the center
–> eyes are usually moving at least a bit, this makes them stop as much as possible - purple fuzzy dots around the edges fade until they disappear
- purple dot with black outline stays!
DOESN’T apply to RIGID borders
–> including the grey square background
Neural explanation for gradual contours disappearing without retinal motion?
- eyes usually move –> neurons that detect edges would cross the fuzzy contours and detect them
- without movement, and no solid borders, neurons don’t see them, and they fade out
Why are we sensitive to biological motion?
- we’re social animals
- being able to detect motion is a key part of communication with other people
- communication is essential for survival
Evidence that we’re sensitive to biological motion?
- point light walker
- can detect bio motion with very low spatial frequency
- human movement is very effective in advertisements
Motion onset captures attention meaning? Evidence? Maybe reason why?
- people are very sensitive / pay attention when things START to move
- people were quickest to identify letter target when it began to move
Why? –> could be alive!
Animate motion def? Why does it capture attention? Evidence?
- Animate motion = movement by something that’s alive
- It captures your attention bc its more likely to be relevant to your survival
- people pay more attention to spot showing animate (self controlled)
How is a simple neural circuit to detect motion designed? Preferred…? (3 things)
- 2 neurons with diff. receptive fields link to one neuron (M)
- there is a delay in the connection between 1&M, but no delay between 2&M
- the delay means that the signal from 1 arrives at the same time as 2
^ this only works if the motion moves from the receptive field of 1 first and then 2 at the right speed
- M will have a preferred orientation, direction, and speed
2 types of eye movements?
- saccadic eye movements (or saccades)
- smooth pursuit eye movements
Saccadic eye movements (saccades) def?
Brief, rapid eye movements that change the focus of gaze from one location to another
Smooth pursuit eye movements def?
Eye movements made to track a moving object or to track a stationary object while the head is moving
Saccadic suppression def?
The visual system’s suppression of neural signals from the retina during saccadic eye movements
Evidence that we take eye movements into account? (Afterimage)
- bright light –> afterimage on retina
- look around the room
- after image “moves” b/c you move your eyes
- RETINAL POSITION of the afterimage CAN’T change
–> eyes (and head) signal movement, but there’s no change on retinal stimulus
–> you see movement
Eye movement experiment monkey –> what does it give support for?
- we take eye movement into account when perceiving motion
- we can distinguish between object moving / eyes still & eyes moving / object still
- retinal movement =/= perceived movement
Eye movement experiment monkey –> what are the 2 set ups? What are the results (activity) ?
Version 1:
- monkey fixates straight ahead
- object moves through receptive field
- significant/high activity in neuron
Version 2:
- object is stationary
- monkey moves eyes from spot 1 –> 2
- monkey’s receptive field crosses over the object
- there’s some, but very limited activity, just above baseline
Real-motion cells def?
- Neurons that signal actual movement of an object in the environment
- they combine retinal information with information about eye movements
2 theories on how we account for eye movements?
- Inflow
- Outflow
Inflow theory meaning?
- info about eye movement is sent from EYE MUSCLES (themselves) to the brain
Outflow theory meaning?
- superior colliculus is responsible for telling the eyes when/how to move
- a COPY of those COMMANDS is sent from the superior colliculus to the brain
- COPY is called corollary discharge signal
Corollary discharge signal?
- Copy of an eye-movement command from the superior colliculus (sent to other parts of the brain/visual system)
- informs visual system about upcoming eye movements
- ensures stable visual experience even during eye movements
Important “assumption” to distinguish between theories? (when would we have info?)
INFLOW:
- says we ALWAYS have accurate info about the behavior and position of our eyes
- even if they’re doing something weird, we’d know
OUTFLOW:
- we ASSUME our eyes have ONLY done what we asked it to do based on CDS
- we would NOT know if they were doing something weird
Inflow/outflow experiment 1: “Fixed objects, passive eye movements”
What does this mean? What does each theory predict?
- objects in a room don’t move
- tap on eye to make it wiggle
Inflow: you DON’T see movement, you know your eye is moving and account for it
Outflow: you DO see movement, you can’t tell your eye is moving
Outflow :)
Inflow/outflow experiment 2: “Fixed objects, paralyzed eye, attempt to move eyes”
What does this mean? What does each theory predict?
- objects in room don’t move
- eye is physically paralyzed
- the person is trying to move the eye (ie. sending brain signals that the eye should be moving, but it’s held in place)
Inflow: DON’T see movement –> you know eye isn’t moving
Outflow: DO see movement –> you think your eye should be moving cuz your brain says so, you see the world as moving
Outflow :)
Inflow/outflow experiment 3: “Image fixed on retina, passive eye movements”
What does this mean? What does each theory predict?
- Afterimage is used so it can be fixed on the retina
- you tap your eye
Inflow: DO see movement –> afterimage is fixed on retina, you know the retina is moving with the eye
Outflow: DON’T see movement –> you didn’t tell your eye to move, image is attached to eye –> no movement
Outflow :)
More evidence for outflow? Experiment?
Neurons with receptive fields can have anticipatory responses to stimuli in the NEW location
–> where their receptive field is ABOUT to be, right after a saccade
5 movement illusions?
- movement after effects
- aperture problem
- apparent movement
- induced movement
- self-produced actions
Movement aftereffect def? 2 examples?
- after viewing movement in one direction for a long time, if you look at a stationary object, it may appear to move in the OPPOSITE DIRECTION as the movement you were just observing
- waterfall example
- spiral example
Neural explanation for movement aftereffect?
- circuit for movement requires the combination of 2 neurons –> the DIFFERENCE of the signals of the 2 make up the signal of the M neuron
- when perceiving motion in one direction for long enough, one of the “feeder” neurons gets fatigued
- after you look away from the motion, the fatigued neuron fires BELOW BASELINE
–> RESULTING in a M neuron that gives the appearance of motion in the OPPOSITE DIRECTION
Aperture problem meaning?
How can a cell (like one in V1) that only has a small receptive field (“aperture”) and only sees movement in its preferred direction detect 2 directional movement?
Aperture problem solution?
The neurons that detect motion in MT have much larger receptive fields than the cells in V1
PATTERN cells combine info from V1 cells to determine the true direction of movement
Component cells def?
Signal the direction of movement at a SINGLE contour
(located in V1 and MT)
Pattern cells def?
Combine information from different component cells (in V1 or MT) to get complete information about the direction of movement of an object
Apparent movement def? Ex?
- 2 stimuli separated in TIME and LOCATION are perceived as a single stimulus moving between the two locations
- ex. 2 dots “moving” back and forth
Bi-stable apparent motion (or quartet)
- symmetric kitty corner dots flip flop
- you can see vertical or horizontal motion
- covering half the dots can change the direction of movement
Ternus display –> 2 types, what’s the basic premise?
- there’s 2 (or 3) dots
- One is in the center, it never “moves,” just blinks on or off
- One is on the left, one is on the right
^^ L&R dots blink on ALTERNATING, so you only see 2 at a time
Types:
1. Group motion
2. Element motion
Ternus display –> Group motion
What is it? When does it happen?
- you think there is a “group” of 2 dots that’s being SHIFTED
- you think the L dot becomes M dot, and M dot becomes R dot
Happens when interval is LONG (>50ms)
Ternus display –> Element motion
What is it? When does it happen?
- you see middle dot staying STILL
- outside dot is rapidly SWITCHING sides
Happens when interval is SHORT (<50ms)
Occluded jumping dot scenario?
- Theres a bunch of dots on the screen that are flickering to give the illusion of apparent motion
- in one spot, one of the dots doesn’t appear, because there is a red square in its place
- instead of thinking there just wasn’t a white blinking dot there, you perceive the white dot as moving BEHIND the red square
Sort the following into a LOW level and HIGH level systems:
a. element motion
b. random dot kinematogram
c. occluded jumping dot
d. motion before form
e. group motion
f. form before motion
Low level:
a. element motion
d. motion before form
b. random dot kinematogram
High level:
e. group motion
f. form before motion
c. occluded jumping dot
Induced movement def?
- illusion where you think something is moving because its surroundings are moving
Ex:
- the dot moving up and down in the square moving in a circle looks like its also moving in a circle or diagonal shape
- if a big semi truck next to you starts moving forward, you might think your car is slowly rolling backwards (self-induced motion)
Self produced actions affect perceived movement meaning? Evidence for…?
- illusion where if you move your hand, you can change the direction you perceive movement
- evidence that perception is tied to action
