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Lecture 6

Lecture 6

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Susanne Ferber

Lecture 7: 309 – Cortical Streams of Processing: + ventral stream travels to the temporal lobe + dorsal stream goes to the parietal lobe – theories of object recognition: + view-dependent frame of reference: - template theory – recognize it - to recognize an object, we have to have representations of it in multiple different frames - view-dependent - depends on the viewpoint that we've seen it – angles - can call upon the template to recognize the object + view-invariant frame of reference: - geon theory - when looking at an object... look at the geons that make it up - see the geons and recognize the object at this angle, etc – Dependent vs. Invariant? + repetition suppression - see a object and brain activity occurs ... few seconds later, see it again and have less brain activity relative to the first time – idea of repetition suppression activity + task: show people objects with same orientation or different orientation... shows different parts of brain that shows sensitivity - see a new object, have a high brain activity... same view, less brain activity... but different view, there's high amount of brain activity again (treating it like a completely different object) in the right fusiform area (bottom part of temporal lobe) – dependent. More template-like - new object emits high brain activity, but same view and same object in a different view has lower brain activity – invariant. Left fusiform area, more geon-theory like. + each hemisphere processes information in slightly different ways – Representing complex objects at the neural level: + Gnostic hypothesis: “grandmother cells” + when looking at a person, one neuron corresponds and activates .. → recognize the person - idea that you have one cell when activated, corresponds to perception of grandmother. When see grandmother, activate all sorts of feature about her (ie: face shape/hair) and this constellation of brain activity, all of these features that corresponds to grandma... when activated together, they activate the grandmother self, the cells that corresponds to grandma. - thinking about grandma... - seeing different features of an object, activate agnostic cell, and when the single cell is activated, perceive the given stimulus + ensemble coding hypothesis: - instead of having a grandmother cell, you have lots of features that activate together - to recognize grandma, picking up same features an agnostic cell would but there isn't some cell that's “grandma” - perceiving all these features that make up grandma & this constellation of activity leads you to say it's grandma – Category-specific loss of knowledge? + herpes virus coming into the brain... demolishes the temporal lobes;; selective to both sides + show objects to people with the damage and ask to describe it → not specific, general. + damage to temporal lobes... - temporal lobes linked to concept knowledge... different categories of knowledge spread across different parts of the temporal lobe - knowledge of the people is stored in the front part of the lobe - knowledge of animals is stored a little bit further back - knowledge of tools is even further back. + see how it lines up to impairments... if you damage the front and the back, you're more likely to have damaged the middle as well. – Object recognition is an incredibly important process that relies on high-quality visual input and the ability to link this input to stored conceptual knowledge – How is knowledge stored? Evidence seems to be favoring ensemble coding but lesion studies might tempt us into thinking there is a “Ryan Reynolds” cell in our brain.. – The Corpus Callosum: + left and right hemispheres don't do exactly the same thing – modest specialization exists (ie: motor system) + right side of body controlled by left frontal lobe + attention more specialized in right hemisphere; language in left + separation difficult to probe + purpose: connects the two hemispheres together – whatever the right side of brain knows, left knows quite transfer = information transfer done at light speed + epilepsy... seizures that don't have current underlying cause - grand mal seizures... involves involuntary motor movements – body shakes. Person loses consequences, cease for a certain amount of time and wake up confused. Can have multiple seizures per day depending on severity. There's anti-epileptic medication that reduce excitability of brain, works well on some people. + can cut out part of a brain that's responsible for generating seizures... problem: many seizures come from medial temporal lobe (involves hippocampus – hotspot for seizures). - taking it out is really undesirable... fix one problem, create another. + callosotomy: cut the corpus callosum, the bridge between the two hemispheres. - reduce the spread of seizure... contain it to one side of the brain - people more likely to respond to medication, seizures reduced – Surgical resection of the corpus callosum + front, back or middle of it can be cut + have to cut part of the skull and brain to reach the corpus callosum – Functional subdivisions of corpus callosum: + divided by types of information it transfers + frontal part of the corpus callosum transfer motor information – corresponds to frontal lobes (have motor corticies) + somatosensory area that corresponds to the parietal lobe (Posterior midbody) + auditory for temporal lobe (Isthmus) + Splenium is for occipital lobe + Rostrum – higher cognitive? + Nowadays, just cut the front of corupus callosum. If you cut the anterior midbody, clinical results are just as the same as cutting the whole brain → cut little as possible and get maximum results + when cutting the corpus callosum, each side of the brain is going to try and do their own thing – difference in processing, specialization between the two hemispheres → “Split brain patients” + Tachistoscopic Presentation: split brain patient sits and stares at a screen. Information presented on the screen so quickly that you can't even move your eyes – whatever's on the right visual field is going to the left side of the brain …. Left side of brain knows something that the right doesn't know;; vice versa. Can isolate knowledge information to one hemisphere or both. - key and ring presented;; key on left, ring on right. Can recall the object seen on the right visual field that goes to the left hemisphere. Never says key – right hemisphere cannot talk. - when asked to grab the object he had seen with his right hand, grabs the ring – whatever he can say, he can grab it with his right hand. - when asked to grab the object he had seen with his left hand, grabs the key – right hemisphere controls knowledge by moving the left hand. When asked why he grabbed the key, he's not sure/tries to make up a story that explains his behavior. - when right hemisphere does something and left hemisphere doesn’t know why, left tries to make sense of it – reason. + when seeing a horse on LVF, draws a saddle instead with the left hand – semantically related. Right hemisphere controls the left hand to draw. – Looking at faces composed of fruits/vegetables: + right hemisphere better at holistic whole-processing of faces. – Degree of information transfer in the corpus callosum: + Normal brain: receive the stimulus on the left side to the right hemisphere. But the information crosses over to the left so you can say what it is. + Complete split: information contained in right he
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