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The role of attention in conscious access mechanisms and their influence on visual representation : evidence from psychophysics and fMRI

Abstract : A major finding in the scientific study of conscious perception has been the existence of two temporally-distinct phases of visual processing. The first, characterized by the feed-forward propagation of evoked activity in early visual cortex, is not typically associated with conscious perception. The second phase involves a reactivation of early sensory cortex by downstream regions and is often cited as a correlate -- if not a proximal cause -- of consciousness. This raises a few crucial questions: firstly, what causes this feedback process to emerge, and secondly, what distinguishes a stimulus representation that has undergone such feedback processing from one that has not ? At the time of writing, two competing theories have been proposed. The first theory, hitherto referred to as "early-and-local", posits that conscious access emerges from the very emergence of a feedback loop between high-level sensory cortex and its primary counterpart, and that this cortical resonance is driven entirely by upstream activations along the feed-forward chain. This implies that only those stimuli that exhibit high salience from the onset can become conscious, and by extension, that the stimulus' reportability is governed entirely by early evoked activity in primary sensory cortex. "Late-and-global" theory, by contrast, posits that conscious perception is the direct result of routing of information through a distributed cortico-cortical network called the Global Neuronal Workspace (hereafter GNW). By this account, visual information in various local cortical regions is given access to routing infrastructure by some selective process, namely attention. In 2013, Sergent and colleagues tested a prediction derived from this second model: that an arbitrary sensory representation that has initially failed to become conscious can be hooked into the GNW by means of an attentional manipulation. To do this, a low threshold target Gabor patch was presented, followed by an extrinsic cue either at the location in which the Gabor had been presented, or on the opposite side of the screen. Subjects were better at discriminating the orientation of the Gabor in trials where the cue had been presented on the same side as the target, and also reported seeing the target more clearly, suggesting that the retrospective intervention of attention was enabling a weak signal to gain access to the global neuronal workspace. We present data from psychophysical modeling and functional magnetic resonance imaging that point to a causal role for attention in the emergence of a conscious percept, with implications for the structure of perceptual representations in early sensory cortex.
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Louis Thibault. The role of attention in conscious access mechanisms and their influence on visual representation : evidence from psychophysics and fMRI. Cognitive Sciences. Université Sorbonne Paris Cité, 2016. English. ⟨NNT : 2016USPCB225⟩. ⟨tel-02042613⟩

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