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Visual Perception.docx

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McMaster University
Judith Shedden

rdJanuary 23 2013 Psych 2H03 Human Learning and Cognition Visual PerceptionPerceptionSensationvisual stimulusprojects on retinatwo dimensional representationdifferent colours and levels of brightnessour perception goes far beyond the information givenour visual system is not like a camerawe sample select parts of the visual world and we build up our own interpretationone of the assumptions that the brain makes is that the world is very stable filter properties that arent important to identify the object and holds constant the characteristics that do help to identifywe see the world in terms of objectsthe visual stimulus colours lines does not consist of objectsa lot of processing needs to be doneNecker Cube edges corners we see a cube that has bystable perceptionPattern Recognitionrecognition or identification of patternsa pattern is a complex configuration of sensory signalssequences of sounds recognized as words music associated with semantics emotionconfiguration of visual features recognizedHow do we Recognise Patternshow important is direct experienceWe are easily and quickly able to recognise an object even though it is in an orientation we have never seen beforeat early stages is effortless automaticwe are usually not even aware of the basic sensory signal but only of the meaningthere is a lot going on to produce thisfeedforward information flowattention and what you are expecting can feedback and change the neural response at lower levelswhat we see can be effected by what we expect to seeComponents of Visual Perceptionform perception what is itdepth perception where is itmotion perception what is it doingdorsal stream where motion actionventral stream what object leads to areas that recognize objectsHow doe we Recognise Patternswhich comes firstGlobal to local recognitionRecognize the whole followed by the partsLocal to global recognitionIdentify parts when construct the wholebottom up and topdown processes both contribute to pattern recognitionwhat is the contribution of datadriven processing bottomup due to raw sensory input lower levels o datadriven bottomup automatic perceptual processes o Our visual system attempts tp organize the visual signals o The perception of the pattern switches continuously among several pattern alternatives o The array seems to seethe with motionconceptuallydriven processingthJanuary 25 2013 OnOff and OffOn Receptive Fields and Phi Phenomenonstimulating neurons with different kinds of center surround fields onoffoffonas things are moving across these receptive fields there can be lateral inhibition which contributes to movementPhi phenomenon lights coming on and off at the right timing we can perceive it as motionParsinginitially we perceive the figure as a whole Embedded features are perceived if the overall form is parsed in a particular way If we know what we are looking for we can impose that order on the stimulusif we impose topdown processes we can parse the image in any way we wantA theres a 4 we process global faster than localB theres a parallelogram When parsing goes array camouflage trying to mess up the parsing of the prey or predatorPerceptionSensationfeatures of objects are perceives as constant despite continual changes in the retinal images of the objects
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