Lecture 5- Binding and Schizophrenia Flashcards
What are of the occipital lobe is invovled in colour perception?
V4
Why is colour perception important?
It has an adaptive function: allowed us to determine what was safe/ ripe to eat. Could also help in terms of mate selection and predator recognition.
What did Pessoa et al. (2014) show about predator detection in a dichromat versus a trichromat?
A dichromat missing the red cone had a better than chance ability to detect the predator (in the four images) but was worse than the trichromat with 3 cones who got it nearly 100% of the time.
What is area V5 invovled in?
Motion detection
What did patient M.P. show? Why is this rare?
Showed that V5 is invovled in motor detection as had bilateral lesions of V5. With this their colour and form perception remained intact but they saw motion in static frames not as continuous fluid movement (think teacup). This is known as Akinetopsia.
Rare because you have to damage V5 on both sides and its a very small area so the chance of damaging even just 1 is rare.
What is V5 in monkeys called?
MT
What does direction turning of an MT neuron show?
Neurons in the MT region of a monkeys cortex (equivalent to V5 in humans) are specific to a certain direction of movement i.e. they fire more when an object moves one way as opposed to another.
As well as direction of movement what other component of movements are MT/ V5 neurons specific to?
Speed
In terms of specificity of V5/MT neurons to direction and speed of motion what do we need to keep in mind about the overall movement?
Each neuron will be tuned to a slightly different speed/ direction. Therefore, collectively all the speed/ directions will be covered to create an accurate representation of movement overall.
What is the value of motion detection?
- Captures attention
- Segments foreground from background.
- Helps compute the distance to various objects in the scene (if something is closer to you will move faster across your visual field/ rate of change determines distance)
- Helps in computing the 3D shape of an object (see from different angles/ points)
- Allows estimation of the direction in which you are heading within the scene (optic flow)
- Allows recognition and prediction of actions (could be vital for survival e.g. predators, hunting or in social situations)
What is looming? What problem does it cause?
- The closer you get to an object the faster the expansion of that object gets (think skydiving when just jumped from plane despite covering lots of distance the ground does not look significantly closer with each second but once you get close to the ground it suddenly appears closer and closer).
- Problem in driving when car stops ahead of you: can’t tell it’s stationery until the last possible moment which could cause you to hit the car in front if you don’t react fast enough.
How do we generally tell how far away something is?
By how much space it takes up in our visual field: more space= closer
Explain the sentence: object perception requires processing in parallel pathways. What problem does this create?
We need V1 info about orientation, motion information from V5, shape from the IT cortex and colour information from V4. Somehow all this information from different areas needs to come together to create a single unified image. What’s more if there are multiple objects how does the brain link certain features to the particular object they are associated with. This is known as the binding problem.
How is temporal binding a solution to the binding problem?
-Temporal binding is the idea that distributed neural responses are tied together by the coordinated timing of their firing patterns.
-This synchrony is often associated with repeated, oscillatory activity
-Cells firing in synchrony form “cell assemblies” that collectively represent a given object at a moment in time
-This shared timing tags specific cells as sharing the same “message”
and links the features of an object together
How does the ambiguous of the two faces/ one face and candle stick in center show the idea of temporal binding?
- When see two faces cells from the same side are firing together and thus perceived as the same object (go down). These fire at different times to cells from the opposite side/ other face.
- When 1 face with candle stick in middle is seen cells across the two halves fire at the same time while those at the borders of the candle stick fire at the same time. Cells in the halves fire at different times to cells in the candle sticks.
- What is interesting is that the sensory input is not changing its the same image but our perception of it is changing.
