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PSYB57 Mem & Cog - Ch2

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Matthias Niemeier

What it means to perceive y Sensation and perception provide the raw material for cognitiony Our perception is not a simple registration of sensory stimuli but sophisticated cognitive processes work on the sensory information almost immediately and produce the brains interpretation our existing knowledge guides these dynamic processesy The sensory stimuli are typically ambiguous and open to multiple interpretationsy The two problems with sensation and perception 1 Sensory input does not contain enough information to explain our perception 2 The world presents us with too much sensory input to include into our coherent perceptions at any single momenty We do not just register the picture as a whole when we see an image but we see only relatively fine details in a small regionpoint of fixation Searching is one of the ways to deal with excess inputy We engage in selective attention which allows us to choose part of the current sensory input for further processing at the cost of other aspects on inputy In conclusion whether too much or too little cognitive processes are necessary to interpret and understand the material we encounterHow it works The case of visual perceptiony Vision like hearing is a distance sense that helps us sense objects without touching them It tells us what is out there and where is ity Our senses also give us a nudge towards action eg where to grab the object fromy Visual perception takes in information about the properties and locations of objects so we can make sense of it and interact with our surroundingsStructure of the visual system y The pattern of light intensity edges and other features in the visual scene form an image on the retina y Light hits the photoreceptors and nerve cells at the back of the eye job light gets converted into electrochemical signalstransmitted to the brain via optic nerves each optic nerve is a bundle of long axons of ganglion cells in the retinaoptic nerve axons contact with LGC lateral geniculate nucleus in thalamus a structure lying on the surface of the brainPrimary visual cortexstriate cortexhost of visual areas as well as areas that are not exclusively visual in functiony Beyond the primary visual cortex 2 pathways can be identifieda Dorsal pathway reaches up into parietal lobes and is important in processing information about where items are located and how we act on them eg touch them1 b Ventral pathway reaches down into parietal lobe and processes information that leads to recognition and identification of objectsTopDown and BottomUp processing y Most visual areas that send output to another area also receive input from that area ie they have reciprocal connectionsy Reciprocal connections lead to the idea that perception is the product of bottomup and topdown processesy Bottomup processes are driven by sensory input from the physical worldy Topdown processes seek and extract sensory information and are driven by our knowledge beliefs expectationsy All acts of perception involves both bottomup and topdown processing eg visual search depends on the surrounding objectsy Perceptions are interpretations of what we see and and the mental representations are produced by the interaction of bottomup and topdown processingLearning to see y The interpretations of the world around us is determined by the interaction between our biological brain and experience y Visual system of an infant typically fixates for about half a second and this visual information starts to accumulate and force lasting mental representations of objects people and places y The early stages of life have critical period during which particular responses must develop otherwise that ability will fail to properly developy The sensory input of a person competes for representation in the cortexBuilding from the bottom up From features to objects Processing Features the building block of perceptions y Visual features includes spots and edges colors and shapes movements and texturesthey are the building blocks of perceptiony In bottom up processing we look at an object and count the features so that we can figure out the processing that takes place to comprehend the image Spots and Edges This feature is processed by the ganglion cellsneurons in the retinas whose axon fibers form the optic nerveLight lands on the receptive field of the photoreceptors clusters of photoreceptors are linked to ganglion cells of retina that pass on the information to the optic nerve 2
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