Anchoring visual subjective experience in a neural model: The coarse vividness hypothesis
Highlights
► Initial subjective experience is coarse but meaningful and integrated. ► Initial subjective experience could be related to gist perception at the top of the feed-forward sweep. ► Later feed-back processing would mediate detailed conscious vision for goal-oriented behaviour. ► Objective measures tapping onto details do not probe initial subjective experience.
Introduction
Perceptual subjective experience refers to the way the world appears to us via our senses. It is an intuitive notion, fundamentally constitutive of our human nature. We all share the intuition that a robot, however smart, is lacking any feeling associated with the complex operations that it can execute: a robot is not human, therefore it lacks subjective experience. Subjective experience nevertheless remains an elusive notion, difficult to frame in a scientific theory, since it is essentially a private experience, that is not easily accessible to the experimenter. Nagel (1974) famously illustrated this idea by pointing out that even if we were an expert about the machinery of a bat, we could not imagine what it is like to be a bat, what it feels like to be a bat, or more generally what it feels like to be anyone else. Here, we concentrate on subjective visual experience, the sensation that sometimes accompany neural visual processing (Kanai & Tsuchiya, 2012).
In the last 20 years, the search for the neural correlates of consciousness has been very active. Leaving aside concepts and theories, most studies on visual consciousness adopted a pragmatic approach (Crick & Koch, 1990), and contrasted neural responses to stimuli that were consciously perceived vs. stimuli that remained unnoticed. But what does such a contrast tell us about visual consciousness? Does it pertain to information processing that could take place in a robot, or does it pertain to the neural basis of subjective experience? Since these questions were most often not explicitly addressed, subjective visual experience remains an underspecified issue in cognitive neuroscience. On the other hand, the nature of subjective perceptual experience is hotly debated from a theoretical point of view. Some philosophers argue that subjective experience is a cognitive illusion (Dennett, 1991, O'Regan and Noe, 2001), a post-hoc cognitive reconstruction rather than an immediate experience (Cohen and Dennett, 2011, Dehaene et al., 2006), whereas others emphasize that subjective experience is central to consciousness and is distinct from cognitive abilities (Block, 2007). At the other end of the spectrum, many visual scientists do actually study consciousness without mentioning it, since any study on explicit visual perception pertains to visual consciousness.
In this paper, we review neural and behavioral studies on visual recognition, whether or not addressing directly and explicitly the issue of subjective experience, and show how the architecture of the visual system constrains conscious perception. In the light of those constraints, we propose that the distinctive feature of initial subjective experience is coarse vividness: initial subjective experience is rich, integrated and meaningful, but does not contain much details. We provide a physiologically plausible model that accounts for this property and that articulates the quality of subjective experience with neural information processing. We then show how two intensely debated issues in consciousness research, namely the interpretation of change blindness studies and of the Sperling experiment, and the dissociation between attention and consciousness, can be parsimoniously interpreted in the framework of the coarse vividness hypothesis.
Section snippets
The disputed status of subjective experience
Subjective experience is at the heart of a vivid theoretical debate questioning the possibility that conscious experience exists independently of cognitive functions. Some argue that consciousness is reducible to cognitive functions (Cohen and Dennett, 2011, Kouider et al., 2010). In this functionalist approach, consciousness is mainly considered as a combination of high-level cognitive functions, and, in this view, subjective experience is either absent or thought to arise somehow from the
Specifying the richness of subjective experience
Our spontaneous experience of the visual environment is a rich one. Although this richness has not been measured by the conventional tools of experimental psychology, both subjects' spontaneous reports and our own everyday experience point to vivid contents of consciousness. As nicely expressed by Biederman (1972), “if we glance at the world, our subjective impression is of clear and almost instantaneous perception and comprehension of what we are looking at”. The clarity and richness of
Existence of integrated percepts without details
The coarse vividness hypothesis requires the existence of integrated, meaningful percepts that are nevertheless devoid of specific details. This stands in contrast with our intuition that the contents of our visual perception are detailed. However, as pointed out by the Gestalt theory, the very existence of visual illusions indicates that perception is a construction that produces integrated and meaningful entities. Because we all spontaneously perceive those visual illusions, this idea seems
Explanatory power of the coarse vividness hypothesis
In the framework of the coarse vividness hypothesis, two intensely debated issues in consciousness research, namely the interpretation of change blindness studies and of the Sperling experiment on the one hand, and the dissociation between attention and consciousness on the other hand, can be parsimoniously re-interpreted.
Conclusions
We relate here a classical model of visual processing backed up by numerous experimental findings in vision research with experimental results and ongoing theoretical controversies in consciousness. The articulation between consciousness studies and the physiology of the visual system appears to be centered on the core concept of “richness of representations”.
We propose that the defining property of initial subjective experience is coarse vividness. The richness of initial subjective experience
Acknowledgements
This work was supported by a grant “NonExCo” from Agence Nationale de la Recherche (ANR-BLAN-12-BSH2-0002-01). We thank the reviewers for their insightful and constructive comments.
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