Refining the methodology for investigating the neural correlates of consciousness
Date
2015-10-02
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Abstract
Küsimust selle kohta, mis on teadvus, peetakse kaasaegse teaduse viimaseks tõeliselt suureks probleemiks, sest senini pole mitte keegi suutnud selgitada, miks ja kuidas aju töö on seotud teadvuselamustega. Tänapäeval on üldiselt aktsepteeritud, et teadvuse mõistmiseks on esimese sammuna tarvis täpsemalt määratleda ja tundma õppida teadvuse neuronaalseid korrelaate – neid ajuprotsesse, mis on minimaalselt tarvilikud mingi kindla teadvuselamuse jaoks. Antud väitekirjas on sellele eesmärgile kaasa aidatud nägemistajuga kaasnevate teadvuselamuste neuronaalsete korrelaatide ning nende markerite uurimise kaudu.
Kuna on tõenäoline, et varasemate uurimuste tulemused ei peegelda mitte ainult teadvuse neurokorrelaate, vaid ka neile süstemaatiliselt eelnevate või järgnevate protsesside korrelaate, püüti käesolevas töös neid kaasnevaid protsesse täpsemalt uurida ning osades katsetes metodoloogilistel eesmärkidel hoopis vältida. Selleks kasutati varasemast hoolikamalt planeeritud katseparadigmasid, tulemuste töötlemise uusi võtteid ning mitmekesisemat loomulikku pildimaterjali. Lisaks võeti arvesse neurovõrgustike pidevalt muutuvat dünaamilist seisundit ja selle mõju teadvustamise protsessidele.
Kokkuvõtvalt võib öelda, et väitekirjas kajastatud uurimustööde tulemuste järgi hakkavad visuaalsete teadvuselamuste vahetud neuromarkerid ilmnema umbes 200 ms jooksul pärast visuaalse stimulatsiooni jõudmist võrkkestale. Samas võib teadvuselamuste kujunemine aga olla hoopis järkjärguline protsess, sest teadvusega korreleerub usaldusväärselt ka umbes 100 ms hilisem neuromarker. Lisaks viitavad tulemused sellele, et visuaalse süsteemi keeruline dünaamika tuleb kõige paremini esile realistliku pildimaterjaliga, mitte lihtsate ja kunstlike geomeetriliste kujunditega. Inimajus on talletunud ohtralt eelteadmisi reaalse visuaalse maailma ning selle reeglipärasuste kohta. See informatsioon mõjutab juba väga varajases faasis nägemistaju ja teadvustamise protsesse, neid täiendades ning parandades.
Consciousness is the biggest unsolved problem of modern science because no one has successfully explained how the concerted firing of brain cells is able to produce our subjective experience of the world. It has been argued that in order to understand this phenomenon better we must first identify the neural correlates of consciousness – those neural events which are jointly sufficient for producing a specific conscious experience. The present thesis was set to contribute to this research effort by investigating the neural correlates and markers of conscious visual perception. It is likely that previous studies have failed to identify the true correlates of consciousness because their results also contain processes that systematically precede or follow conscious experience, but do not directly reflect consciousness itself. Thus, the current aim was to study these additional processes in more detail or to even avoid their contribution is some studies. To that end more carefully designed experimental paradigms and more realistic stimulus material was employed. Furthermore, the ongoing state of more global neural networks and its influence on conscious perception was taken into account. Together the results demonstrate that neural markers of conscious visual perception begin to arise about 200 ms after the visual image reaches our eyes. It is however possible that conscious perception is a gradual phenomenon proceeding step-by-step, because another marker also reliably correlates with conscious visual perception around 100 ms later. Furthermore, some results indicate that the complex dynamics of our visual system are best observable with realistic images and not to the same extent with simple and artificial figures. The brain retains a lot of prior knowledge about the natural visual world and its regularities. This information influences the processes of conscious perception early on by complementing and correcting them.
Consciousness is the biggest unsolved problem of modern science because no one has successfully explained how the concerted firing of brain cells is able to produce our subjective experience of the world. It has been argued that in order to understand this phenomenon better we must first identify the neural correlates of consciousness – those neural events which are jointly sufficient for producing a specific conscious experience. The present thesis was set to contribute to this research effort by investigating the neural correlates and markers of conscious visual perception. It is likely that previous studies have failed to identify the true correlates of consciousness because their results also contain processes that systematically precede or follow conscious experience, but do not directly reflect consciousness itself. Thus, the current aim was to study these additional processes in more detail or to even avoid their contribution is some studies. To that end more carefully designed experimental paradigms and more realistic stimulus material was employed. Furthermore, the ongoing state of more global neural networks and its influence on conscious perception was taken into account. Together the results demonstrate that neural markers of conscious visual perception begin to arise about 200 ms after the visual image reaches our eyes. It is however possible that conscious perception is a gradual phenomenon proceeding step-by-step, because another marker also reliably correlates with conscious visual perception around 100 ms later. Furthermore, some results indicate that the complex dynamics of our visual system are best observable with realistic images and not to the same extent with simple and artificial figures. The brain retains a lot of prior knowledge about the natural visual world and its regularities. This information influences the processes of conscious perception early on by complementing and correcting them.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
teadvus, teadvusseisundid, nägemistaju, visuaalne maskeerimine, elektroentsefalogramm, transkraniaalne magnetstimulatsioon, consciousness, states of consciousness, visual perception, visual masking, electroencephalogram, transcranial magnetic stimulation