Motion Flashcards
Where is motion processed?
Starts in V1 and extends into dorsal pathway “where”
Where is motion not detected?
the retina or LGN
Where is motion mainly detected?
V5/MT:
Responds to motion of anything
Direction and speed tuned
Motion contrast cells
What are the two ways to see motion?
Inflow
Outflow
Describe inflow
Eye muscle signal theory (Sherrington)
Motion from actual eye movements (slow)
Describe outflow
Brain signal theory (Helmholtz)
Motion from intention to move eyes (fast)
What are opponent motion detectors?
the brain detects motion by comparing the movement in opposite directions
What do opponent motion detectors respond to?
the balance between motions cells preferring opposite directions
What is Apparent motion?
A series of still images showing displacement of an object over time will appear as fluid motion
When does apparent motion occur?
Only occurs if the time difference and displacement are sufficiently small
- Problems arise when the delay between images interact with the speed of the object
What is Motion after affect?
Looking at something moving then looking at something still but still seeing that motion effect after the fact
(also names the water illusion)
What is the principle of univariance?
Cells can only produce a single output (the firing rate)
What is the problem with the principle of univariance
cells can sometimes be driven by two different dimensions
Cells cannot separate speed and contrast (or frequency and intensity)
Thus its difficult to differentiate two stimuli with the same input
What do motion cells respond strongly to?
high contrast stimuli and faster motion
Does perceived speed reduce with reduced contrast?
Yes, at least for some stimuli including looming and receding objects i.e cars.
Does motion have similar cells to centre surround cells sensitive to motion contrast ?
Driven by direction in the centre but inhibited by the same direction of motion in the surround
the cell is very excited when the area of movement is small and the more you enlarge that area the cell becomes inhibited
When are centre surround cells for motion contrast at its maximum activity
when the surround is moving in the opposite direction to the centre of the cell
Describe induced motion and vection
When we see a large area of moving stimulus we don’t know if it is us moving or the world
When is induced motion and vection common?
motion is slight and acceleration smooth
What is illusory motion
The sensation of motion in a static stimulus
The motion after-effect is one kind of illusory motion
What is pure illusory motion
the sensation of motion in an entirely static stimulus even without adaptation
What is the aperture problem?
If you view a moving stimulus through a small window (aperture) such that you can only see one edge of the stimulus, you will only see motion at right angles to the edge
Why does the aperture problem occur?
Motion cells in area V1 have small receptive fields and only respond to short edges.
So they can only signal motion at right angles to their preferred orientation
(the mask mimics the small receptive fields of V1 cells)
When does sensitivity to motion develop?
10-12 weeks.
When does Rudimentary visual flow develop?
6-8 weeks (unable to discriminate motion direction/ can perform smooth pursuit
When is rapid development of motion?
6-14 weeks
What is looming stimuli
things that might collide with the child are detected at a very early age and may even be present at birth
What is blindsight?
Damage to visual cortex
Blind but can sense motion due to the projections from LGN to V5/MT
What is the opposite of blindsight
damage to V5/MT we can still see but we are unable to sense motion
What is Akinetopsia?
Loss of area MT makes you motion blind
The world perceived as a series of still photographs
What does losing V1 result in?
functionally blind but you can still respond to some stimuli - especially movement
What does losing V3 result in?
damage your motion perception but not destroy it
What does Losing MST/V6 result in?
inhibit navigation but not motion
