I argue that conscious visual experience consists in a direct and noninferential grasp of the way one’s current perceptual contact with the environment poises one to pursue various intentional plans, goals and projects. I show that such a view of visual consciousness is supported by current work in cognitive neuroscience, affords a compelling account of colour perception, and suggests a way to bridge the ‘explanatory gap’ between consciousness and the language of the natural sciences. In chapter 1, I examine the reasoning that leads to the appearance of an explanatory gap between the phenomenal and the physical in more detail, and set out the constraints on a solution that our discussion of the problem has imposed. I then sketch the two rival takes on the relationship between perception and action mentioned above – adjudicating between these two theories (and finding in favour of the action-space view) is the task of the next two chapters, and is a recurring theme throughout. Chapter 2 moves on to discuss some recent work in the neuropsychology of vision and what it might suggest about the functional role of conscious vision, and the first half of chapter 3 considers two puzzle cases concerning colour perception. Each of these discussions turns out to constitute a source of support for the actionspace view that visual perception consists in a grasp of the practical consequences of sensation, and the second half of chapter 3 sets out this view and responds to an initial range of questions and objections it might face. Chapter 4 illustrates our view via a discussion of colour perception, and chapter 5 discusses the type of grasp of practical consequences that is necessary for perceptual sensitivity to issue in conscious experience. By chapter 6, we are in a position to see how the action-space approach can help close the explanatory gap for phenomenal consciousness, and our final chapter sets out how I think this should be done. I conclude with a brief discussion of further questions and prospects for the action-space approach.

The phenomenal experience of our visual perception, what it is like to be in that state, is something that we might take for granted. However, looking closer at the neural correlates of visual processing in relation to phenomenal experience we recognize that it is a complex issue. Whether our subjective experience of our visual representation of the world is attached to cognitive functions, like working memory and attention, or whether some sort of richness overflows such functions, is an ongoing debate within cognitive neuroscience. Advocates for overflow argue that phenomenal experience is the result of activity in posterior occipito-temporo-parietal areas and is independent of attention, while those within the non-overflow position mean that for phenomenal awareness to arise activity in higher-level areas like the prefrontal lobe is needed. Finding evidence for unattended visual phenomenal consciousness without access consciousness would support the overflow position since it could indicate phenomenal experience as independent of attention. In addition to this debate, researchers need to keep in mind what methods are being used to measure phenomenal experience, since several biases potentially follow studies using introspective measures. Through this systematic review, a search string provided empirical studies based on fMRI that investigated unconscious and conscious visual processing. The results of this review show little or weak evidence for unattended visual phenomenal consciousness and do not seem to overflow cognitive functions.

Les stimuli naturels projetés sur nos rétines nous fournissent de l’information visuelle riche. Cette information varie le long de propriétés de « bas niveau » telles que la luminance, le contraste, et les fréquences spatiales. Alors qu’une partie de cette information atteint notre conscience, une autre partie est traitée dans le cerveau sans que nous en soyons conscients. Les propriétés de l’information influençant l’activité cérébrale et le comportement de manière consciente versus non-consciente demeurent toutefois peu connues. Cette question a été examinée dans les deux derniers articles de la présente thèse, en exploitant les techniques psychophysiques développées dans les deux premiers articles. Le premier article présente la boîte à outils SHINE (spectrum, histogram, and intensity normalization and equalization), développée afin de permettre le contrôle des propriétés de bas niveau de l'image dans MATLAB. Le deuxième article décrit et valide la technique dite des bulles fréquentielles, qui a été utilisée tout au long des études de cette thèse pour révéler les fréquences spatiales utilisées dans diverses tâches de perception des visages. Cette technique offre les avantages d’une haute résolution au niveau des fréquences spatiales ainsi que d’un faible biais expérimental. Le troisième et le quatrième article portent sur le traitement des fréquences spatiales en fonction de la conscience. Dans le premier cas, la méthode des bulles fréquentielles a été utilisée avec l'amorçage par répétition masquée dans le but d’identifier les fréquences spatiales corrélées avec les réponses comportementales des observateurs lors de la perception du genre de visages présentés de façon consciente versus non-consciente. Les résultats montrent que les mêmes fréquences spatiales influencent de façon significative les temps de réponse dans les deux conditions de conscience, mais dans des sens opposés. Dans le dernier article, la méthode des bulles fréquentielles a été combinée à des enregistrements intracrâniens et au Continuous Flash Suppression (Tsuchiya & Koch, 2005), dans le but de cartographier les fréquences spatiales qui modulent l'activation de structures spécifiques du cerveau (l'insula et l'amygdale) lors de la perception consciente versus non-consciente des expressions faciales émotionnelles. Dans les deux régions, les résultats montrent que la perception non-consciente s'effectue plus rapidement et s’appuie davantage sur les basses fréquences spatiales que la perception consciente. La contribution de cette thèse est donc double. D’une part, des contributions méthodologiques à la recherche en perception visuelle sont apportées par l'introduction de la boîte à outils SHINE ainsi que de la technique des bulles fréquentielles. D’autre part, des indications sur les « corrélats de la conscience » sont fournies à l’aide de deux approches différentes. / Natural stimuli impinging on our retinas provide us with a wealth of visual information. This information varies along “low-level” features, such as luminance, contrast, and spatial frequency (SF). Whereas some of this information reaches our awareness, some of it is processed in the brain without us ever becoming aware of it (i.e., non-consciously). A remaining question is precisely which SFs influence brain activation and behavior consciously vs. non-consciously. The aim of this thesis was to address this question using state-of the-art psychophysical techniques. The first article introduces the SHINE (spectrum, histogram, and intensity normalization and equalization) toolbox for controlling low-level image properties in MATLAB. The second article describes and validates the SF Bubbles technique, which was used throughout the studies in this thesis to map SF tuning for various face perception tasks with a high SF resolution and low experimental bias. The third and fourth articles focus on SF processing as a function of awareness. In the former, SF Bubbles was employed together with repetition priming and masking to investigate which SFs are correlated with observers’ behavioral responses during conscious vs. non-conscious face-gender perception. The results show that the same SFs significantly influenced response times in both prime awareness conditions but, surprisingly, in opposite ways. In the latter, SF Bubbles was combined with intracranial recordings from awake human patients and Continuous Flash Suppression (Tsuchiya & Koch, 2005). This allowed us to map the SFs that modulate activation in specific brain structures (the insula and the amygdala) during the conscious vs. non-conscious perception of emotional facial expressions. The results for both regions demonstrate that non-conscious perception relied on low SFs more and was faster than conscious perception. The contribution made in this thesis is thus two-fold: methodological contributions to visual perception research are made by introducing the SHINE toolbox and the SF Bubbles technique, and insights into the “informational correlates” of consciousness are provided from two different angles.

Les stimuli naturels projetés sur nos rétines nous fournissent de l’information visuelle riche. Cette information varie le long de propriétés de « bas niveau » telles que la luminance, le contraste, et les fréquences spatiales. Alors qu’une partie de cette information atteint notre conscience, une autre partie est traitée dans le cerveau sans que nous en soyons conscients. Les propriétés de l’information influençant l’activité cérébrale et le comportement de manière consciente versus non-consciente demeurent toutefois peu connues. Cette question a été examinée dans les deux derniers articles de la présente thèse, en exploitant les techniques psychophysiques développées dans les deux premiers articles. Le premier article présente la boîte à outils SHINE (spectrum, histogram, and intensity normalization and equalization), développée afin de permettre le contrôle des propriétés de bas niveau de l'image dans MATLAB. Le deuxième article décrit et valide la technique dite des bulles fréquentielles, qui a été utilisée tout au long des études de cette thèse pour révéler les fréquences spatiales utilisées dans diverses tâches de perception des visages. Cette technique offre les avantages d’une haute résolution au niveau des fréquences spatiales ainsi que d’un faible biais expérimental. Le troisième et le quatrième article portent sur le traitement des fréquences spatiales en fonction de la conscience. Dans le premier cas, la méthode des bulles fréquentielles a été utilisée avec l'amorçage par répétition masquée dans le but d’identifier les fréquences spatiales corrélées avec les réponses comportementales des observateurs lors de la perception du genre de visages présentés de façon consciente versus non-consciente. Les résultats montrent que les mêmes fréquences spatiales influencent de façon significative les temps de réponse dans les deux conditions de conscience, mais dans des sens opposés. Dans le dernier article, la méthode des bulles fréquentielles a été combinée à des enregistrements intracrâniens et au Continuous Flash Suppression (Tsuchiya & Koch, 2005), dans le but de cartographier les fréquences spatiales qui modulent l'activation de structures spécifiques du cerveau (l'insula et l'amygdale) lors de la perception consciente versus non-consciente des expressions faciales émotionnelles. Dans les deux régions, les résultats montrent que la perception non-consciente s'effectue plus rapidement et s’appuie davantage sur les basses fréquences spatiales que la perception consciente. La contribution de cette thèse est donc double. D’une part, des contributions méthodologiques à la recherche en perception visuelle sont apportées par l'introduction de la boîte à outils SHINE ainsi que de la technique des bulles fréquentielles. D’autre part, des indications sur les « corrélats de la conscience » sont fournies à l’aide de deux approches différentes. / Natural stimuli impinging on our retinas provide us with a wealth of visual information. This information varies along “low-level” features, such as luminance, contrast, and spatial frequency (SF). Whereas some of this information reaches our awareness, some of it is processed in the brain without us ever becoming aware of it (i.e., non-consciously). A remaining question is precisely which SFs influence brain activation and behavior consciously vs. non-consciously. The aim of this thesis was to address this question using state-of the-art psychophysical techniques. The first article introduces the SHINE (spectrum, histogram, and intensity normalization and equalization) toolbox for controlling low-level image properties in MATLAB. The second article describes and validates the SF Bubbles technique, which was used throughout the studies in this thesis to map SF tuning for various face perception tasks with a high SF resolution and low experimental bias. The third and fourth articles focus on SF processing as a function of awareness. In the former, SF Bubbles was employed together with repetition priming and masking to investigate which SFs are correlated with observers’ behavioral responses during conscious vs. non-conscious face-gender perception. The results show that the same SFs significantly influenced response times in both prime awareness conditions but, surprisingly, in opposite ways. In the latter, SF Bubbles was combined with intracranial recordings from awake human patients and Continuous Flash Suppression (Tsuchiya & Koch, 2005). This allowed us to map the SFs that modulate activation in specific brain structures (the insula and the amygdala) during the conscious vs. non-conscious perception of emotional facial expressions. The results for both regions demonstrate that non-conscious perception relied on low SFs more and was faster than conscious perception. The contribution made in this thesis is thus two-fold: methodological contributions to visual perception research are made by introducing the SHINE toolbox and the SF Bubbles technique, and insights into the “informational correlates” of consciousness are provided from two different angles.

Two influential theories of consciousness disagree about if consciousness initially arises along the occipitotemporal cortex to later engage frontoparietal regions and attentional mechanisms, or if it necessarily requires the latter. Consequently, different predictions are made about the temporal emergence of consciousness. The event-related potential (ERP) technique can be used to resolve the issue. It can temporally track neural activity of consciously perceived stimuli relative to stimuli bypassing consciousness. This essay describes the two theories and reviews ERP studies on visual consciousness and its relationship to attention. Three ERP correlates of consciousness have been proposed. The question is if they should be interpreted as supporting the one or the other theory. Most plausibly, visual consciousness arises along occipitotemporal regions and later incorporates frontal areas engaging higher cognitive functions. Importantly it seems that consciousness cannot arise without spatial attention/parietal regions.

Our bodies are arguably one of the most intimate things we will ever know. But the comfort of our own physical boundaries can be altered in various ways. In this analysis, we will look at how vision contributes to the sense of owning a body by analysing six abnormal conditions: the rubber hand illusion, phantom limbs, somatoparaphrenia, the body-swap illusion, out-of-body experiences, and heautoscopy. Examinations of these experimental or pathological conditions has granted a greater understanding of body-ownership. It was discovered that vision plays different modulatory roles, being more intricately involved in full-body ownership than in part-body ownership. Vision appears to be highly connected to self-location and first-person perspective, which both are contributing factors in projecting the sense of ownership to an external location. In part-body ownership, however, vision can be overruled by other senses, such as proprioception. Though it is still able to contribute to the illusion of projecting ownership and proprioceptive displacement to a rubber hand.