Online research in philosophy

Experiments on scene perception and change blindness suggest that the visual system does not construct detailed internal models of a scene. These experiments therefore call into doubt the traditional view that vision is a process in which detailed representations of the environment must be constructed. The non-existence of such detailed representations, however, does not entail that we do not perceive the detailed environment. The “grand illusion hypothesis” that our visual world is an illusion rests on (1) a problematic “reconstructionist” conception of vision, and (2) a misconception about the character of perceptual experience.

Recent work in "embodied, embedded" cognitive science links mental contents to large-scale distributed effects: dynamic patterns implicating elements of (what are traditionally seen as) sensing, reasoning and acting. Central to this approach is an idea of biological cognition as profoundly "action-oriented" - geared not to the creation of rich, passive inner models of the world, but to the cheap and efficient production of real-world action in real-world context. A case in point is Hurley's (1998) account of the profound role of motor output in fixing the contents of conscious visual awareness - an account that also emphasizes distributed vehicles and long-range dynamical loops. Such stories can seem dramatically opposed to accounts, such as Milner and Goodale (1995), that stress relatively local mechanisms and that posit firm divisions between processes of visual awareness and of visuomotor action. But such accounts, I argue, can be deeply complimentary and together illustrate an important lesson. The lesson is that cognition may be embodied and action-oriented in two distinct - but complimentary - ways. There is a way of being embodied and action-oriented that implies being closely geared to the fine-grained control of low level effectors (hands, arms, legs and so on). And there is a way of being embodied and action-oriented that implies being closely geared to gross motor intentions, current goals, and schematic motor plans. Human cognition, I suggest, is embodied and action-oriented in both these ways. But the neural systems involved, and the size and scope of the key dynamic loops, may be quite different in each case.

We seem, or so it seems to some theorists, to experience a rich stream of highly detailed information concerning an extensive part of our current visual surroundings. But this appearance, it has been suggested, is in some way illusory. Our brains do not command richly detailed internal models of the current scene. Our seeings, it seems, are not all that they seem. This, then, is the Grand Illusion. We think we see much more than we actually do. In this paper I shall (briefly) rehearse the empirical evidence for this rather startling claim, and then critically examine a variety of responses. One especially interesting response is a development of the so-called ‘skill theory’, according to which there is no illusion after all. Instead, so the theory goes, we establish the required visual contact with our world by an ongoing process of active exploration, in which the world acts as a kind of reliable, interrogable, external memory (Noe, Pessoa and.

In this paper we focus on the modularity of visual functions in the human visual cortex, that is, the specific problems that the visual system must solve in order to achieve recognition of objects and visual space. The computational theory of early visual functions is briefly reviewed and is then used as a basis for suggesting computational constraints on the higher-level visual computations. The remainder of the paper presents neurological evidence for the existence of two visual systems in man, one specialized for spatial vision and the other for object vision. We show further clinical evidence for the computational hypothesis that these two systems consist of several visual modules, some of which can be isolated on the basis of specific visual deficts which occur after lesions to selected areas in the visually responsive brain. We will provide examples of visual modules which solve information processing tasks that are mediated by specific anatomic areas. We will show that the clinical data from behavioral studies of monkeys (Ungerleider and Mishkin 1984) supports the distinction between two visual systems in monkeys, the 'what' system, involved in object vision, and the 'where' system, involved in spatial vision.

David Milner and Melvyn Goodale’s dissociation hypothesis is commonly taken to state that there are two functionally specialized cortical streams of visual processing originating in striate (V1) cortex: a dorsal, action-related “unconscious” stream and a ventral, perception-related “conscious” stream. As Milner and Goodale acknowledge, findings from blindsight studies suggest a more sophisticated picture that replaces the distinction between unconscious vision for action and conscious vision for perception with a tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. The combination excluded by the tripartite division is the possibility of conscious vision for action. But are there good grounds for concluding that there is no conscious vision for action? There is now overwhelming evidence that illusions and perceived size can have a significant effect on action (Bruno & Franz, 2009; Dassonville & Bala, 2004; Franz & Gegenfurtner, 2008; McIntosh & Lashley, 2008). There is also suggestive evidence that any sophisticated visual behavior requires collaboration between the two visual streams at every stage of the process (Schenk & McIntosh, 2010). I nonetheless want to make a case for the tripartite division between unconscious vision for action, conscious vision for perception, and unconscious vision for perception. My aim here is not to refute the evidence showing that conscious vision can affect action but rather to argue (a) that we cannot gain cognitive access to action-guiding dorsal stream representations, and (b) that these representations do not correlate with phenomenal consciousness. This vindicates the semi-conservative view that the dissociation hypothesis is best understood as a tripartite division.

We seem, or so it seems to some theorists, to experience a rich stream of highly detailed information concerning an extensive part of our current visual surroundings. But this appearance, it has been suggested, is in some way illusory. Our brains do not command richly detailed internal models of the current scene. Our seeings, it seems, are not all that they seem. This, then, is the Grand Illusion. We think we see much more than we actually do. In this paper I shall (briefly) rehearse the empirical evidence for this rather startling claim, and then critically examine a variety of responses. One especially interesting response is a development of the so-called ‘skill theory’, according to which there is no illusion after all. Instead, so the theory goes, we establish the required visual contact with our world by an ongoing process of active exploration, in which the world acts as a kind of reliable, interrogable, external memory (Noe, Pessoa and Thompson (2000), Noe (2001). The most fully worked-out versions of this response ( Noe and O’Regan (2000), O’Regan and Noe 2001) tend, however, to tie the contents of conscious visual experience rather too tightly to quite low-level features of this ongoing sensorimotor engagement. This (I shall argue) undervalues the crucial links between perceptual experience, reason and intentional action, and opens the door to a problem that I will call ‘sensorimotor chauvinism’: the premature welding of experiential contents to very specific details of our embodiment and sensory apparatus. Drawing on the dual visual systems hypothesis of Milner and Goodale (1995), I sketch an alternative version of the skill theory, in which the relation between conscious visual experience and the low-level details of sensorimotor engagement is indirect and non-constitutive. The hope is thus to embrace the genuine insights of the skill theory response, while depicting conscious visual experience as most tightly geared to knowing and reasoning about our world..

Machine generated contents note: -- 1. Introduction -- Consciousness and Sensorimotor Dynamics: Methodological Issues -- 2. Computational consciousness, D. Ballard -- 3. Explaining what people say about sensory qualia, J. Kevin O'Regan -- 4. Perception, action, and experience: unraveling the golden braid, A. Clark -- The Two-Visual Systems Hypothesis -- 5. Cortical visual systems for perception and action, A.D. Milner and M.A. Goodale -- 6. Hermann Lotze's Theory of 'Local Sign': evidence from pointing responses in an illusory figure, D.R. Melmoth -- Understanding Agency and Object Perception -- 7. Two visual systems and the feeling of presence, M. Matthen -- 8. Spatial coordinates and phenomenology in the two-visual systems model, P. Jacob and F. de Vignemont -- 9. Perceptual experience and the capacity to act, S. Schellenberg -- Perception and Action: Studies in Cognitive Neuroscience -- 10. Why does the perception-action functional dichotomy not match the ventral-dorsal streams in anatomical segregation: optic ataxia and the function of the dorsal stream, Y. Rossetti et al -- 11. Mapping the neglect syndrome onto neurofunctional streams, G. Vallar and F. Mancini -- 12. Motor representations and the perception of space: perceptual judgments of the boundary of action space, Y. Delevoye-Turrell -- The Role of Action and Sensorimotor Knowledge in Sensorimotor Theories of Perception -- 13. Vision without representation, A. Noe -- 14. Sensorimotor knowledge and the contents of experience, J. Kiverstein -- Boundaries of the Agent -- 15. Extended vision, R. A. Wilson.

David Milner and Melvyn Goodale, and the many psychologists and philosophers who have been influenced by their work, claim that ‘the visual system that gives us our visual experience of the world is not the same system that guides our movements in the world’. The arguments that have been offered for this surprising claim place considerable weight on two sources of evidence — visual form agnosia and the reaching behaviour of normal subjects when picking up objects that induce visual illusions. The present article shows that, if we are careful to consider the possibility that a demonstrative gesture can contribute content to a conscious experience, then neither source of evidence is compelling.

How should we characterize the functional role of conscious visual experience? In particular, how do the conscious contents of visual experience guide, bear upon, or otherwise inform our ongoing motor activities? According to an intuitive and (I shall argue) philosophically influential conception, the links are often quite direct. The contents of conscious visual experience, according to this conception, are typically active in the control and guidance of our fine-tuned, real-time engagements with the surrounding three-dimensional world. But this idea (which I shall call the Assumption of Experience-Based Control) is hostage to empirical fortune. It is a hostage, moreover, whose safety is in serious doubt. Thus Milner and Goodale (1995) argue for a deep and abiding dissociation between the contents of conscious seeing, on the one hand, and the resources used for the on-line guidance of visuo-motor action, on the other. This ‘dual visual systems’ hypothesis, which finds many echoes in various other bodies of cognitive scientific research, poses a prima facie challenge to the Assumption of Experience-Based Control. More importantly, it provides (I shall argue) fuel for an alternative and philosophically suggestive account of the functional role of conscious visual experience.

Neuropsychological findings used to motivate the “two visual systems” hypothesis have been taken to endanger a pair of widely accepted claims about spatial representation in visual experience. The first is the claim that visual experience represents 3-D space around the perceiver using an egocentric frame of reference. The second is the claim that there is a constitutive link between the spatial contents of visual experience and the perceiver’s bodily actions. In this paper, I carefully assess three main sources of evidence for the two visual systems hypothesis and argue that the best interpretation of the evidence is in fact consistent with both claims. I conclude with some brief remarks on the relation between visual consciousness and rational agency.