Üllatusest tardunud: ennustava töötluse teooria testimine virtuaalreaalsuse abil
Date
2017
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Abstract
Viimaste aastate jooksul on tekkinud palju uusi teooriaid, et muuta praegust arusaama, kuidas aju tajub ja töötleb erinevaid stiimuleid. Senine tõekspidamine väidab, et aju ootab passiivselt sensoorseid stiimuleid, mida seejärel töödeldakse hierarhiliselt käitumise kontrollimiseks. Senist uskumust püüab asendada ennustava töötluse teooria, mis väidab, et aju kui süsteem on alati aktiivne ning püüab pidevalt ennustada sensoorseid stiimuleid, selle asemel, et neid passiivselt oodata. Ennustava töötluse teooria kohaselt saab hierarhiline süsteem sisendiks tajutavaid kõrvalekaldeid ennustatavast olekust ehk ennustusvigu. Selle teooria kohaselt on liigutuse näol tegemist ennustusvea vähendamisega, muutes päris sensoorset sisendit liigutuse abil selliselt, et ta vastaks ennustatud sensoorsele sisendile. Antud teooria kohaselt ei tekita liigutust mitte motoorne käsklus, vaid soov vähendada ennustusviga kavatsetavas liigutuses. Sellest tulenevalt võib öelda, et iseenda liigutamiseks tuleb sensoorset sisendit alla suruda. Teisisõnu selleks, et liigutus saaks aset leida, on vajalik vähendada tähelepanu liigutuse poolt tekitatud tajukogemustele. Kui tajukogemusi pole võimalik alla suruda, siis ei tohiks liigutus aset leida. Antud töö eesmärgiks on testida just seda sama ennustava töötluse teooria raames püstitatud oletust. Täpsemalt üritasime takistada taju allasurumist liigutuse vältel, kasutades uusimat virtuaalreaalsusetehnoloogiat. Valminud katsekeskkonnas esitasime katsealustele ülesandeks reageerida keskkonnast tulevatele stiimulitele käe tõstmisega. Proovisime mõjutada stiimulile reageerimiseks kuluvat reaktsiooniaega, muutes ümbritseva keskkonna visuaalset tähelepanutõmbavust.Eksperimendi käigus kogutud esialgsed andmed ei toeta selgesõnaliselt ennustava töötluse teooriat. Saadud tulemuste hägusust võib selgitada vähene katsealuste hulk ning seetõttu ka väiksemahuline andmekogum, mis ei ole piisav kindlate järelduste tegemiseks. Lisaks on võimalik, et keskkonna tähelepanutõmbavus oli liialt madal ning seetõttu ei õnnestunud sellega segada taju allasurumist. Tulemusi võisid mõjutada paljud faktorid, kuid katsekeskkonna täiendamine avab kindlasti palju võimalusi antud teooria põhjalikumaks uurimiseks.
In recent years, there have been new theories to change the current understanding of how the brain perceives and processes stimuli. The long-standing belief has been that the brain passively waits for sensory stimulation and the received signals are processed in a hierarchical manner to control behaviour. Instead, a theory called active inference states that the system is always active and rather than waiting for the sensory stimulation, it tries to predict it beforehand. According to this theory, the crucial input to the hierarchical system is based on perceived deviations from the predicted state also known as prediction errors. This means that an action is a way of minimizing the prediction error by trying to fit the actual sensory input to the predicted one instead of it just being a response to an input. According to this theory movement is not triggered by motor commands, but instead by trying to minimize the prediction error in the intended movement. This means that in order to move it is required to suppress the sensory input. In other words, it is necessary to withdraw attention from the actual sensory consequences of the movement to allow for movement to happen. If such withdrawal cannot happen the movement should not take place. The goal of this project was to create software to test this peculiar prediction of the theory. In particular, we tried to interrupt the withdrawal of attention during movement in an experiment using the latest virtual reality technology. In the produced environment people were presented with a task to raise their arm as a reaction to stimuli they received from their surroundings. By manipulating the saliency of the visual environment we tried to affect the reaction time of the movement.Our preliminary findings, however, do not provide clear enough evidence to support the theory of active inference. It could be explained by the small amount of data collected, which might not be sufficient enough to draw conclusions from. Additionally, the saliency of the shapes might have too little impact on disturbing the process of sensory attenuation. Many different factors might be at play here, but the experiment is up for improvements and allows for the theory to be studied further.
In recent years, there have been new theories to change the current understanding of how the brain perceives and processes stimuli. The long-standing belief has been that the brain passively waits for sensory stimulation and the received signals are processed in a hierarchical manner to control behaviour. Instead, a theory called active inference states that the system is always active and rather than waiting for the sensory stimulation, it tries to predict it beforehand. According to this theory, the crucial input to the hierarchical system is based on perceived deviations from the predicted state also known as prediction errors. This means that an action is a way of minimizing the prediction error by trying to fit the actual sensory input to the predicted one instead of it just being a response to an input. According to this theory movement is not triggered by motor commands, but instead by trying to minimize the prediction error in the intended movement. This means that in order to move it is required to suppress the sensory input. In other words, it is necessary to withdraw attention from the actual sensory consequences of the movement to allow for movement to happen. If such withdrawal cannot happen the movement should not take place. The goal of this project was to create software to test this peculiar prediction of the theory. In particular, we tried to interrupt the withdrawal of attention during movement in an experiment using the latest virtual reality technology. In the produced environment people were presented with a task to raise their arm as a reaction to stimuli they received from their surroundings. By manipulating the saliency of the visual environment we tried to affect the reaction time of the movement.Our preliminary findings, however, do not provide clear enough evidence to support the theory of active inference. It could be explained by the small amount of data collected, which might not be sufficient enough to draw conclusions from. Additionally, the saliency of the shapes might have too little impact on disturbing the process of sensory attenuation. Many different factors might be at play here, but the experiment is up for improvements and allows for the theory to be studied further.