Week 4 Flashcards
(32 cards)
What does the V1, V3, V5, V6 and MST respond to?
V1/V2 = linear motion and simple stimuli
V3 = motion of complex stimuli (e.g. texture)
V5 = static images that imply motion
V6 = self induced motion
MST = vestibular cues
What is the difference between motion on retina vs motion of retina?
When you track object with your eyes = does not move on retina > moving
When object moves on your retina > stationary
What is the eye muscle signal theory?
Sherrington
- motion from actual eye movements
- slow
- inflow
What is the brain signal theory?
Helmholtz
- motion from intention to move eyes
- fast
- outflow
What is apparent motion?
A series of still images showing displacement of an object over time will appear as a fluid motion
How do we see motion in movies?
One image appears every 40ms which tricks our brain into seeing motion
How do we detect motion?
Light is detected by receptive field A, then goes through a time delay and compare before being recognised at receptive field B
Why do we have a time delay when we detect motion?
Because receptive field A and B can’t be activated simultaneously
What cell is used for motion selectivity in MT?
Opponent motion cell
How do opponent motion cells work?
They have tuning towards a preferred direction, however, if movement is opposite the cell is then inhibited
How does normal motion work?
Spokes (small pics) are the same as the object moves so quickly
What does a fast moving wagon wheel look like? Why?
As if it is going in the opposite direction, as you think the spokes are going backwards when they are just going very far forward
When does apparent motion occur?
When the time difference and displacement is sufficiently small
When do problems occur in apparent motion?
When the delay between images interacts with the speed of object
When does sensitivity to motion develop?
10-12 weeks
What is motor blindness akinetopsia?
Loss of MT = motion blind
Loss of V1 = functionally blind (respond to some stimuli)
Loss of V3 = impede motion perception
Loss of V6 = inhibit navigation
What is illusory motion?
The sensation of motion in a static stimulus
What is an example of illusory motion?
motion after effect
Describe an example of the motion after effet
When we view an image going downwards, we get so used to it that when we look at another image it appears to go upwards, as our downward receptors have been inhibited (adapted)
What have we discovered about the perception of speed over space?
Perceived speed in the periphery is much lower than in the fovea
10 seconds later perceived speed reduced
What are the implications of our perception of speed?
Our judgements are more accurate before adaptation than afterwards
Motion in the periphery fades over time
What is the principle of univariance?
Cells cannot separate speed and contrast
Why is it difficult to differentiate two stimuli with the same output?
Because motion cells respond more strongly to high contrast stimuli and respond more strongly to fast motion
Does perceived speed reduce with reduced contrast?
Yes at least for some stimuli including looming and receding objects e.g. cars
