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Consciousness and perceptual decision-making: The relationship between first- and second-order processing

par Achoui, Dalila
Président du jury Destrebecqz, Arnaud
Promoteur Cleeremans, Axel
Publication Non publié, 2019-02-20

Thèse de doctorat

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Résumé :

Chapter 1 starts with providing the theoretical background against which the experimental work in this thesis can be viewed. It provides the main approaches, theories and views on consciousness and the main challenges in the field. Specifically, it does so in relation to first-order and second- order neuronal processing, which will be explained later on. Furthermore, Chapter 1 discusses the conscious brain in its larger context of an embodied mind and the environment in which the agent lives. Lastly, the final section reviews the possibility of consciousness being a social construct. Chapter 2 continues with examining what happens when information-processing is limited to first-order processing, which is the case when information remains subliminal. Subliminal information does get processed up to a certain level, since brain activity in response to the stimulus can be measured. Yet, it is not processed up to the level that renders the stimulus conscious. The study presented in Chapter 2 aims to answer whether perceptual information presented below the conscious threshold can still affect behaviour? The outcome of this and similar studies would tell us more about the possible functions of consciousness. If subliminal stimuli are not able to influence behaviour, it would suggest that consciousness is necessary in order to guide or regulate human behaviour. Chapter 3 discusses how (changes in) perceptual content influences the subjective experience of time, a concept that is highly related to consciousness. Consciousness inevitably needs a reference or content to be conscious of. Similarly, time needs external physical events to occur to have any meaning, since time is generally only defined in terms of changes of state, mass or energy. Atomic clocks measure time by detecting changes in energy levels of electrons in atoms and are the most accurate timekeepers we have with an error rate of only 1 second per 30 million years. Therefore, no matter how small the event is, without any such event like a change in physical state of the electron the concept of time would be meaningless. Thus, the concept of time would be completely irrelevant in a universe without mass or matter. In such a universe the passing of a single nanosecond would be exactly the same as a billion years. This dependence on external events is what makes time perception such an interesting topic to study in the field of consciousness. The critical question here is how subjective experience of time relates to conscious (changes in) perceptual content.Chapter 4 further explores the relationship between perceptual content and consciousness. The study described in this chapter examines the transition of first-order information to second-order processing. Does a gradual increase in first-order perceptual evidence result in similarly gradual judgments of subjective experience? This chapter discusses levels of representation, perceptual evidence and their effect on subjective judgments. The key question here is whether increasing perceptual evidence while maintaining a fixed level of representation will result in higher levels of subjective measures as well or whether such measures only increase with higher levels of representation. In short, can you be more or less conscious in a graded manner or is consciousness an all-or-none type of phenomenon? This answer will have important consequences for distinguishing between the main theories on consciousness since their predictions about graded consciousness differ and therefore could be strongly challenged by the answer to this question. Chapter 5 tests the idea of consciousness being an acquired ability rather than an innate property of the brain by examining the possibility of training or improving second-order processing, which is one of the key assumptions of the Radical Plasticity Theory. The study described in this chapter explores plasticity of consciousness by performing a perceptual learning study of multiple sessions over several days. The effects of this training paradigm on both first- and second order processing will be discussed in this chapter. Chapter 6 looks deeper into such second-order subjective judgments and what kinds of first- order information is used to make such judgments. It has been suggested that such measures of conscious experience not only incorporate sensory information but also includes information from non-sensory brain areas such as the motor cortex. In light of the sensorimotor accounts of consciousness the influence of motor cortex, and thus action, on the subjective experience of visual stimuli would be an important result and would support such accounts wherein perception and action are tightly intertwined. Finally, chapter 7 summarizes the main findings and discusses the results within the larger framework or first- and second order processing. It also addresses the consequences or implications of these findings for some of the most promising theories on consciousness, and Radical Plasticity thesis in particular.