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NATS 1860 Note 14

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Natural Science
NATS 1860
Keith Schneider

NATS 1860 Note 14 Visual Cortex: Objects and Actions - Review of Retina - Lateral Inhibition and edges - Neurons in visual cortex - Orientation and motion - Migraine visual auras - Cortical pathway for action. - Cortical pathways in using vision for object recognition Marijuana Receptors - Effective chemical THC is a cannabinoid – it’s effective because we have receptors in several different areas of our brain (protein molecules in nerve cells) o They are present in the basal ganglia and the cerebellum are involved in the coordination of motion  There are some people who walk as if they're drunk when they’re not drunk o It affects aspect of memory because it affects the hippocampus o It affects your appetite as the hypothalamus (neurons that release chemicals into blood to regulate internal organs - There are receptors in the brain that sense the different levels of chemicals in the blood in order to release different chemicals into the glands of the body. Results of Experiment one - Orientation discrimination: 2o to 3o – orientation selective neurons in V1 o This is good because this shows that there are cells sensitive to different orientation in our primary visual cortex - Why were there eight alternatives instead of just two? o It was to make it harder in order to confuse the students, thus to reduce the probability of corrective guessing - Eye movements: two types. You can’t voluntarily decide which you’re going to use o One: when there’s something moving in the world you can track it (smooth pursuit): it was for the tracking motion of M cells.  You need to process the motion to survive. o Two: jumps (saccades): inspect areas with detail in static scenes of P cells  When there isn’t anything or nothing is moving, to inspect the world your brain uses P cells, which are sensitive to fine detail, to pick an area with high detail and jumps to examine it with high resolution. - Face discrimination o We learned about 6 of 8 faces studied o We correctly rejected about 6 of 8 new faces o We automatically learned the average of the faces that we saw, and learned it better than the faces we actually experienced.  We don’t automatically learn when we’re learning things, what we’re actually learning most effectively is the average of that group. Review of the Retina - Two types of photoreceptors: rods (dim light) and cones (for bright light and colour vision) - There are three types of cone photopigments: red, green, and blue. o Colour blindness (heavily male dominated), are cases where one pigment is missing. - The retina is responsible for light adaptation (negative afterimage) this results from the fact that some retinas are greatly stimulated - The output of the retina has two ganglia cells o The M ganglion cells – fast rest response, large receptive field, and no colour. They see levels of white, gray, and black o The P ganglion cells: slow response, small receptive field, and colour HD vision. They pick up fine detail. - Ganglion cell axons to V1: left side of the world to the right V1 Vanishing of Stationary Images - When we look at patterns for a long time, sometimes the patterns look like they’re vanishing - Neurons adapt completely to images that are stationary on retina - To do this properly, you need a video camera in the laboratory and a computer to find out exactly how the eye moves o You can get the same effect using blurred image in periphery: large receptive fields Retinal Receptive Field - Record from the retinal ganglion cells o Shine spot of light at different points on retina to figure out what stimulates or inhibits it - Receptive field: the area of the retina within which a spot of light changes the firing rate of the ganglion cells o All receptive fields have both excitatory and inhibitory regions Orientation Selective V1 Neuron - Cells in the visual cortex: if information from 3 adjacent ganglion cell provides excitation to a single, that cell is going to respond best to a particular orientation. o That cell will respond best to vertical line of light. o For other orientation of bars, there isn’t as much action potential because it doesn’t fill all of these. - P cells main input to oriented receptive fields. - Any given cell will respond best to a particular orientation or location on retina - Orientation cells sense bars, lines, and edges. o This is important because the way that an object (face, PC, or car) is defined as a pattern of lines and edges o If there were no lines or edges, there would be no lines to see - Our brain is picking out the most important information when defining objects. Orientation Selective V1 Neurons - There are about 12 different orientations represented in V1 - Furthermore, each point in an image is presented by all 12 orientations. o There more than 12 times as many nerve cells (100 times) that there are in our retina sending information to the cortex - They detect lines and edges that form objects. - These cells are genetically programmed as well as early experienced o You’re born blind, so you can’t see very far. o Cells coming in that are active at the same time form synapses that work on the same time. Combining Orientation Cell Responses - What are these images? - Vertical orientation cell responses – guess what the images are. It’s not much information - Horizontal orientation cell responses - Afterwards, the two will be combined to recognize the two o Combining even two orientations is enough information to usually recognize an object - This is - Our brain reorganizes the information into the different orientations, providing an efficient way of defining objects o An object is entirely uniform (consider the white area on the screen) o There’s no valuable information, and the brain needs one piece of information to say how bright it is o All the important information in the edges - It is possible for a person to have damage to a specific orientation o There’s a condition where at birth, the cornea is not part of a sphere, it curves more into one direction than the other. Therefore, vertical orientations will properly work, and horizontal will work. Migraine Auras - This is about 7 times more common in women than in men until menopause and then men start having migraines. - A migraine aura is a visual hallucin
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