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NROC64: Lec 6 - Multisensory perception (nearly word-for-word what was said in lecture).doc

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NROC64 Lec 6 Multisensory Perception Slide 5 IntroMultisensory illusionshow diff senses will actually work togetherHow multisensory integration is implemented in the brain 2 mechanismsoWe have areas where diff unimodal areas flowing together crosstalk significant cxns btn very early brain areas between diff modalitiesoThe cerebral cortex also has multimodal areas have receptive fields for both types of stimuliOscillations better swing together oscillations is one way that connectivity can be established on ongoing basis can actually change depending on needOptimizing perceptionoMaximum likelihood estimationstatisticalintegrating info from diff sources in best possible way info from diff modalities and each of these modalities is imperfectthen combining 2 modalities in some way will give chance of getting something thats better than individual onesoSimple statistical procedure to estimate what is the best possible solutionthis actually closely explains what humans actually dohumans integrate multiple senses in very optimal fashion although not perfectSlide 6 IntroIt makes sense to integrate across diff modalities bc events and objects will convey some forms of changes in energy that goes together not just one form of NRG that changes oAn object may emit light and at the same time give off sound waves these 2 events go together so it makes sense to integrate themorganizes and makes it simpleroAlso helps to improve estimate of direction from which something is atoOr complementary effect can see something in front of you but you cant see behind you but you hear somethingsomething dangerous can turn around and add vision to the audition diff senses will complement each otherSynergy the whole is greater than the sum of its partsoStill possible to understand the whole by studying individual partsoGraphsVisual event as a fxn of time light is turned off and then it is onWhat was recorded in superior colliculus neuron respond to visualauditorymultisensory stimuliSpikeAPYou get some activity simply count theof APs that are caused by the light turning onSame thing for audition have an auditory eventclickSame thingHave both things at the same timeLight turns on and theres a clickGet 1200 more APs neuron responds much more stronglycalled superadditive An old mystery How do our senses work togetherSlide 7We have brain areas specialized for vision sound somatosensation etcBut there are illusions that are crossmodal and multisensory that suggest there are strong interactions between the diff senses how is it possible to have crossmodal illusions despite separate brain areasoSolution 1 feedforward from unimodal areas to later multisensory multimodalheteromodal areas oSolution 2 have crosstalk btn unimodal areas lateral connectionsSlide 9 Multisensory illusions McGurk effectUnder ideal conditions hear dah dahClose eyes hear bah bahTurn of sounds see gah gahSlide 10 McGurk effectAudiovisual illusion where the sound is bahThese are freq plots of energy sound analysis Sound bah in terms of freq is plotted on vertical axis horizontal axistime color codedpower Get bands of higher energy which are very typical for human voicescan tell apart vowels and consonants that way 3 bandswhat it illustrates is that these are actually sounds that are generated by a synthesizeis a continuum between bah and in the in the end gahnoone is saying gah but the video indicates gah in middle is dahsince produced w sythesizer each time that you hear some soundwill have very clear opinion of what youre hearing even at the transitionsthis is categorical perception of speech soundsin audition we have this categorical perceptiondepends on language you grew up w we have a way of sorting sounds into discrete categories even if it is on a continuumMcGurk effect auditory infodah and visual infogah mix that togetherget something in the middleyou dont say that something weird is going on you say you perceive dah in the middleIt also depends on how clear the 2 modalities are depending on that there may be more weight for auditory or visual infoSlide 11 Oculogravic gravity illusionAnother multisensorycrossmodal effectSomething that pilot would experience esp on jet
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