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| Travels in a straight line, acts both as a particle and a wave. We are sensitive to light at 400-700 nm wavelength. All light is part of the electromagnetic spectrum, ranging from Gamma Rays to AC circuits (visual spectrium is only a tiny part of this, going from high energy purple to low energy red) |
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Tubes select only one direction (one ray of light) per particular point. Like a drinking straw (opaque, and has solid light).
Lenses: the speed of light is different in different materials and the light bends when crossing the boundary. Integrate/capture much more light. All the rays reaching the prism bend to converge back at one singular point, making the image. Middle ray is not refracted at all. |
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| Discovered by Ibn Al Haitham. Pinhole optics: in a pinhole camera the pinhole only allows one ray of light to go through per point. On a wall we can recover the image, inverted. But the images are dim because there is very low light, disadvantage. |
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| the same thing as a pinhole camera. upside down picture that is dim (not enough light) although it would make perfect images of the world. |
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| Refraction is the bending of light when it crosses the boundary between two materials, and is proportional to the ratio of the speeds. |
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| All the rays of light that reaches the prism refract and bend to eventually converge back at one singular point. This is what makes the image |
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| Convergence of electromagnetic energy into chemical energy. Early organisms (amoeba proteus and paramoecium) were photosensitive and responded to the light. More complex: flatworm, limpit. Pinhole camera in nature: chambered nautilus. |
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3 types of cones and 1 type of rod
Rods are more sensitive to lower light levels (cones are sensitive to photopic vision).
Rods you can't see much in the center, can see a lot more in the periphery. A lot of low resolution, no color. Diurnal animals have more cones, nocturnal animals have more rods. |
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| Cones are for color. Densely spaced, lot of detail, fall off in the perifery. Color, detailed center |
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| 1 lens per receptor, as many as 125,000 receptors per "eye" |
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| One lens, many receptors; some invertebrates have simple eyes |
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| Limpit/Patella, amoeba, paramecium |
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| limpits and flatworms have no lens but a few hundred receptors. |
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| Chambred nautilus exhibits a "pinhole camera" in nature |
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| Unusual scanning eye; two lenses, two receptors. "the tv of eyes" |
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| bees and flies have compound eyes |
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| squid eyes are like ours but bigger and better |
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| 2 lenses, 260,000,000 receptors. come with iris, pupil, sclera. |
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| Cornea, lens, iris, pupil |
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| cornea has the most focusing power; lens is mainly used for fine tuning. cornea has fixed focusing power, lens is flexible and can adjust. how does it do that?? |
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| Differences between cones and rods |
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cones are bigger and cone shaped. rods are smaller and rod shaped. there are 3 types of cones and 1 type of rods. cones are good for color.
rods are more sensitive to low light (scotopic vision). cones are sensitive to brighter light (photopic vision).
in the fovea, densely packed receptors are for CONES ONLY. blood vessels and nerves are pushed away.
rods predominate the PERIPHERY (everywhere except for the fovea). the blood vessels block some light. |
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| fovea is the focus in the center of your vision; periphery is the blurrier parts on the outside |
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| optic disk is where the nerves (optic nerve) leave the eye; literally a blind spot |
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| when there is no change in the stimulation, then the brain stops responding (fatigue). the brain only cares about change. stop changing, causes the red and green patches to disappear. lower responsiveness in the regions exposed to brighter light then creates a negative version of the image when a black field is viewed. |
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Photoreceptors send messages to other cells in the brain called neurons,which communicate through action potentials. Action potential fires when it receives enough from its neighbors. Triggered electrically when inputs rise ABOVE THE THRESHOLD. Large and brief (all or none, either happens or it doesn't). Propagates to the end of the axon without any decrement.
Like flushing a toilet, sub and supra-threshold input (all or none output). Action potential = spike = firing. |
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| Neurons, neuron structure |
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| Neurons have action potentials, when triggered the neurons send out "spikes." Transmissions speeds up to 100m/s in fast fibers. Called the language of cells. Message is the pattern of the cells that are firing. |
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| Fires when it receives enough communication from its neighbors. Triggered electrodes when inputs rise above the threshold. Large and brief, all or none, either happens or it doesn't. |
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| Communicate through action potentials. |
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| EPSP, IPSP (excitatory, inhibitory connections) |
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EPSP: excitatory post synaptic potential that makes the neurons fire
IPSP: inhibitory post synaptic potential that makes neurons NOT fire |
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| Recording from neurons with an electrode |
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| Measure neuron communications with a micro-electrode |
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| Excitation and inhibition counteract each other |
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| Spike frequency is determined by a balance of excitatory and inhibitory inputs from other cells |
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Collect info from photoreceptors and send the information to the eye. Top layer of cells (neurons).
Averages out information from the crowd of photoreceptors, receiving information from a bundle of photoreceptors. Plot the response for positions of small spots of light on the screen. Receptive field is limited to the receptor itself. Only ONE tiny spot on the screen that projects only to that single receptor. |
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| On skin, there is a region to which a neuron is sensitive. Find a neuron that starts responding when a person's hand is poked in a particulra place. That plot (of the cell's response amplitude/frequency for each location on the skin) is the RF of the cell. The RF for touch is the area of SKIN to which a neuron is responsive |
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| The area on the retina that corresponds to an area of the visual field to which a cell is responsive |
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| Ganglion cell averages information from a crowd of photoreceptors, plot the response of the photoreceptor for positions of small light on the screen. Receptive field is limited to the receptor itself. |
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| Neuron fires more rapidly when light is shown and stops firing at an offset of light |
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| Neuron stops firing when light is shown and starts firing at offset of light |
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| Ganglion cells have circular concentric disc receptive fields that are spatially separate |
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| LGN has six layers. cells have monocular input. layers alternate inputs from each of the two eyes. top four are parvocellular, two layers from each eye. parvo (small) lgn cells receive inputs from SMALL midget ganglion cells. bottom two are magnocellular layers, one from each eye. receive inputs from large parasol ganglion cells. |
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| center-surround receptive fields like retinal ganglion cells. little or no processing beyond that done in the retina. brings in retinotopic maps from both eyes to register to make it easy for cortex to combine inputs from the two eyes. |
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| LGN Cell and RF organization |
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| illusion where you see gray dots at the intersections of the white lines through black squares |
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| LGN RF explanation of Hermann Grid |
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| lateral inhibition between center and surround of receptive field. receptive field at intersection has more light falling on inhibitory surround than field between two black squares. therefore the center has a stronger response than intersection. receptive fields in central fovea are smaller than rest of retina; no dark area when you look directly at the intersection, but dark areas are in your peripheral vision. |
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| Primary visual cortex (V1). the first cortical visual area, where most visual information is processed. Cells are like STRIPES. |
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| slanted rectangles. outsides are +'s and middle stripe is - for off center. opposite for on center. |
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| Discovered oriental cells in 1975. off surround responds to flashes of light. very little spontaneous response to those cells. Orientation selective, not very sensitive to motion. Prefer CONTRAST, difference between light and dark. Experimented on a cat. |
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| Hubel & Wiesel's Discovery |
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| Discovered that simple cells are orientation selective, and not very sensitive to motion. The on center reats ot the bars of light moving across it, response before the illumination is the same as after full illumination, meaning that they care about on and off light, prefer contrast (difference between light and dark) |
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| Simple cell stimulus preference |
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| Doesn't always fire when light is off because the neurons care about what changes. Adaptation demonstration: when cells are presented with something that doesn't change, they go back to their default response and stop changing. |
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| Tuning curve for orientation |
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Sensitive to ORIENTATION.Orientation and position selectivity predictable from arrangement of ON and OFF areas. Most response when light perfectly matches the + stripe down the middle.
Cell's response DRAMATICALLY increases when faced with a straight orientation of bar. |
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| Construction of simple RF from LGN units |
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| in visual cortex. oriented receptive fields, but cannot predict from response to spots. complex cells are orientation selective, but not sensitive to ABSOLUTE position. no response to small spots or diffuse illumination. responds to light or dark bars. |
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| Preferences of complex RF's |
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combine responses of several simple cells (all with same orientation sensitivity) and cover a small region. they are overlapping so that every location has an On response from at least one of the underlying simple cells and an off response from another underlying cell.
excitatory response area is large and not confined. cell responds to bright and dark bars and likes MOVEMENT in cell direction. |
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| Endstopped/hypercomplex cells, RFs |
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| in visual cortex, oriented Receptive Fields. limited length for best response. like directional motion. |
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| Preferences of endstopped cells |
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| likes to be THE PERFECT LENGTH. like directional motion. the bars can't be too long or short. beyond that, the receptiveness begins to drop (opposed to a complex cell, which responds the same no matter what the length is). |
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| Optimal stimulus for complex, simple, hypercomplex |
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| fibers in the brain (middle) |
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| cell bodies of the brain (outsides) |
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| cortical size: 60 cm diameter; like a 23 inch pizza. |
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| a behavior is controlled by a specific brain area; destroying the area selectively destroys the behavior as well |
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| prone to accident was exemplary supervisor of dynamiting crew; following accident he was fitful, foul mouthed, and inconsiderate; unable to hold to plans. frontal lobe was the localized region for planning and emotions. |
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| Broca's patient (tan) could only say the word TAN because he had paralysis on the right side of the body, but he was otherwise intelligent and normal. he just couldn't produce other words because he had localized region of the brain for the production of language, and destroying that area selectively destroys the behavior as well. |
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an early argument for localization; but there was not much to be learned from the surface of the skull.
they mapped out different functions based on the shape of the outside of the skull |
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| frontal lobe, parietal lobe, occipital lobe, temporal lobe |
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| Motor cortex, somatosensory cortex |
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motor: movement.
somatosensory: touch
your two hemispheres interact with eacho ther through the corpus callosum pathway |
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| left hemisphere is responsible for control and sensation on the right side of the body, and the right hemisphere is responsible for control and sensation of the left side of the body. this is called a crossover. |
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| stimulated exposed brain of alert patients during surgery. used a small probe to deliver slight electrical stimulation. different locations evoked different memories, sensations, or muscle twitches. he then used this to plot the first brain maps. expose the brain under anesthesia with the patient completely conscious. a lot of memories can be |
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| your two hemispheres interact with each other through this pathway |
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| the homunculus statue shows us how much of the cortex is devoted to how much of the body (over representation of certain parts of the body) |
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| There's lots of representation in the FOVEAL region. Principle of CORTICAL magnification; some areas are over-represented - especially the fovea. |
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| Somatotopy/motor topography |
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| points that are adjacent to the retina are adjacent on the cortex. |
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| the left visual field projects to right cortex. and vice versa. |
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| to the interior part of the temporal lobe. sensitive to object identity/recognition, identifying what an object is. what: localizing objects. |
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| to the parietal lobe for location, action, navigating, and grasping. (where something is located, and also for grasping action) |
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| Medium scale modules: color, motion, faces |
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COLOR, MOTION, AND FACES
regions of the brain that have cells that are predominantly selective for certain kinds of things. these are the areas that are predominantly sensitive to visual information. |
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