week 4 Flashcards
what happens if an image stays to long on human retina
it disappears
why does the image disappears ?
the eye collects change overtime
how long does it takefor an image to fade when stabilised ?
10-30 sec
what are the two sources of retinal image motion
object move while the eyes are still
objects still, eyes more
explain moving object while the eyes are still work?
if the black dot is fixated, the image of of will fall on the fovea but the image of the will move across the retina
Explain still object and eyes move work?
fixate on a moving object on the fovea casuing stationary patterns to be swept.
why does the retina move a lot?
The retina compensates for our own motion to detect object motion.
What are the three signals telling us about motion?
image on retina which motion stream can detect
feedback from extra-ocular muscles
corollary discharge (expected use)
What can we determine from motion sequence?
Direction and speed
Direction and speed relative to other objects
relative distance
both animate and rigid objects
In terms of light what does the retina detect?
Retina detects the change in light levels overtime.
How is our sensitivity of light measured?
It is measured using temporal frequency
What is our overall sensitivity to flicker supported by?
Both the M and P pathways
What is Reinhardt detector?
Described a way of combining early visual receptive fields to make a direction selective unit
When do humans show direction selectivity in neurones?
Cortical area V1 , except for rabies - retina
In regards to Reichardt: motion in the correct direction
Stimulates the detector - because the first is delayed they overlap
In regards to Reichardt: motion in the wrong direction
Does not stimulate the detector - because they will never going to overall
In regards to Reichardt: Apparent motion is when:
two stationary images displaced with the correct separation in time precent motion
In regards to Reichardt: what is aliasing ?
pairing the wrong image features over time.
How does aliasing occur?
When the respective field don’t match the patterns at time one and two resulting in a different object motion response
How does motion adaption occur?
While viewing a constant signal and reduces sensitivity to that pattern.
Where does adaptation occur in the brain?
In the cortex
Normally a stationary pattern:
Stimulates motion direction detectors equally in all direction
How Representing motion in xt space
The speed of the motion can be represented by the slope of the line
What is reverse Phi motion?
Reflects a paradoxical motion percept
How does reverse Phi work?
sequence alternates in direction of motion after each pair of frame but contrast is inverted every time to the left
What is the first order of sub-systems?
Sensitive to variation across the image
What is the second-order of sub-system?
is sensitive to variation in local contrast and texture
What is the Aperture effect:
A problem at the first stage of motion detection.
detection of motion in small a receptive field returns ambiguous answer
What is intersection of constraints model?
A rigid object that moves produces velocity signals at each edge
How does V1 detect the motion in regards to the intersection of constraints model?
V1 detects the motion at 90˚ to the edge because of the aperture effect.
the motion system combines elements of different orientation
into a Percocet of rigid motions
if the constraint lines don’t cross, then :
the system take the average speed and direction of the motions but doesn’t perceive rigid motion
What is the barber pole illusion ?
the perceived direction changes with orientation
what do the streaks in an image mean?
signals a possible direction
What does grouping mean?
Need to combine signals from detectors at different location to get global motion signals.
What is the dot motion threshold ?
5- 15%
what does MST stand for?
medial superior temporal
What does the MST stage involve?
Combines different directions to determine complex motion flows
What is induced motion?
A failure to fully segment as static stimulus from its moving surround.
what does segmentation do in the brain?
extracts moving objects from a scene - usually our own movement
3D can be used to :
Add depth in the flow field
there is a flow filed in our retinas that
expands outwards as we reach the point we are heading towards
what is biological motion ?
the Process of motion elements that signals the presence of normal bodily motion
What does biological motion require?
a prior knowledge of actions
What is the pricing stream in humans similar to and which stream?
Macaques
in the dorsal stream
What is another name for MT (Middle temporal area)?
V5
What can MT cells determine?
The global flow in a motion target
What where the two tasks Newsome & Pare used?
Global motion - measures coherence levels
Contrast sensitivity - measures contrast needed in grating targets
What does remove MT/M5 impair?
Impairs GM detection but does affect contrast sensitivity
What does the transcrainl magnetic stimulation in humans impact?
Motion perception
How can MT be detected?
fMRI
If MT is missing how can signals react the cortex?
there are other pathways but they take longer
What is evidence for pathways that bypass MT/V5?
Poor on Global Dot Motion task in both half visual fields
Whats 3D structure from motion ?
observer must detect a stricter that varies in depth.
Imagine that you are at Niagara Falls, staring at the falling water for a few minutes. When you look away from the water at the crowd of people, the people seem to be floating upward. What phone,enon have you just experienced?
Motion aftereffect
Which of these brain regions is most specialised for motion processing?
Middle temporal area (area V5/MT)
What is a rare neuropsychological disorder in which the affected individual has no perception motion?
Akinetopsia
If you want a motion detector circuit to respond to faster object motions, which changes should you make to the circuit ?
Increase the distance between the detects and or decrease the time delay
The impression of smooth motion that comes from the rapid alternation of objects appearing in nearby location in rapid succession is:
Apparent motion
What is the “Aperture problem”
Local edge motion seen through a single aperture is ambiguous
What is the motion of an object that is defined by changes in contrast or texture, but not by luminance.
Second-order motion
The motion we interpret as peoplee moving around from a few animated dotes is called _____ motion
Biological motion
An area of the visual system that receives one copy of the order issued by the motor system when the eyes move is called ?
A comparator
Suppose you are in a snowstorm and can tell which way the wind is blowing by what percentage of snowflakes are moving in the same direction. What type of motionn is the most analogous to?
Coherent or correlated global dot motion
