L6 - Motion Perception Flashcards
Why might motion detection be important for our survival?
Because if we see something moving when we were evolving it could be the food we could hunt to eat or it could be a predator trying to kill us. Crucial for survival.
Where in our vision are we most sensitive to motion?
In the temporal frequencies on the peripherals.
More sensitive to motion in the periphery.
How does motion help us locate organisms?
It aids in figure-ground segregation. Something sitting still might be unseeable but when it moves it becomes visible.
How does motion give us information about our position in space?
Through the relative position of objects.
The relative position of objects is retained when moving, but you get a distortion of the images around you which indicates which direction you are moving.
closer objects more blurry in peripherals than further away indicating our location in space.
Define affordance
Who coined the phrase?
Affordance is what the environment offers the individual, what it provides or furnishes, either for good or ill.
James Gibson
What is Optic Flow?
The pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer and a scene.
Why does optic flow work to help us determine where we are?
Over time we have learned the statistical regularities of our environment (how things are). We learn to determine which objects should be doing what (trees should be still etc.) and therefore we can learn where we are as we move through space.
What is segmentation?
Why is motion useful for it?
Division into separate parts or accounts.
Motion allows us to see what is connected (one thing, e.g. an animal that is moving) and what is separate.
What is apparent motion?
Making the illusion of motion.
e.g. Animations, using frame by frame pictures
What is translational motion?
Translational motion is the motion by which a body shifts from one point in space to another
Why is apparent motion theoretically significant for psychologists?
It means that that ‘physical’ does not equal perception.
- We do not see what actually is but we put it together. Our brain makes an inference.*
- Gestalt: The whole is greater than the sum of its parts*
What does this image represent?
How our visual processes work.
The neural pathways of how we see.
What is the LGN (lateral geniculate nucleus)?
The relay centre in the thalamus for the visual pathway.
What are the 3 layers of the LGN (lateral geniculate nucleus)?
P-cells - parvocellular layer
K-cells - koniocellular layer
M-cells - magnocellular layer
What pathway is the motion pathway?
What cells deal with motion?
V5 pathway deals with motion (dorsal stream (parietal region))
M-cells (magnocellular) deal with motion.
What does this image represent?
Explain what all the different parts are.
How we code the motion information.
Motion direction is very important.
The green box is receptor field (bar is moving in a specific direction)
If you change the orientation of the bar you are changing the direction of movement and the tuning and range of motion of which the neuron changes its firing rate is broad.
It likes 45-degree motion and weak responses at almost vertical. Likes about a 40 degree of motion.
What did Barlow and Levick (1965) discover about ganglion neuron firing rates?
They found when the bar in the receptive field of our retina moved from A-B there was a big firing rate, but B-A was a weaker response.
- Our receptive field sees one way better.*
- Our base cells in the retina are receptive to motion, our neurons can tell us reliably about what direction we are going.*
- Suggested a building block for motion models.*
How might you create a model of motion detection?
You have two spatially separated detectors.
Take the input of one, with a time delay, and compare it to the other detector.
Motion can be detected if the signals reach the ‘detector’ at the same time.
Determine how fast something is moving by the difference in the detectors
How do our eyes detect motion?
We have a comparitor neuron that is listening to the output between A-B. There is effectively a delay in the signal that A sends back.
- The compare neuron has a slight delay and then compares what neuron a and neuron b saw and then signals it has moved (processes information from both A-B at the same time using a delay)*
- Our entire visual field is tiled with these detectors.*
How do we determine direction selectivity in a simple motion model?
You put two comparator neurons together with a delay on both sides. Then you can determine which way if both neurons arrive at the same time.
(Comparator neurons are looking at two separate detector neurons where one has a delay and fire when they arrive together, indicating the delayed on has moved)
Explain each of the 4 pictures of what is happening and what your brain is telling you about the direction of movement.
Top left: you can tell there is motion but you don’t know where it’s going.
Top right: Left temporal delay means you can tell its moving from left to right
Bottom left: Right temporal delay means it’s moving from right to left.
Bottom right: If you want to tell if it’s moving to the left or to the right you need to be able to have a time delay on both sides so you can compare.
