This overview discusses the nature of perceptual illusions with particular reference to the theory that illusions represent the operation of a sensory code for which there is no meaningful ground truth against which the illusory percepts can be compared, and therefore there are no illusions as such. This view corresponds to the Bayesian theory that “illusions” reflect unusual aspects of the core strategies of adapting to the natural world, again implying that illusions are simply an information processing characteristic. Instead, it (...) is argued that a more meaningful approach to the field that we call illusions is the Ebbinghaus approach of comparing the illusory percept with a ground truth that is directly verifiable as aberrant by the observer in the domain of the illusory phenomenology. This concept of direct verifiability not only provides an operational definition of “illusion”; it also makes their interactive observation more effective and informative as to the perceptual processes underlying the illusory appearance. An expanded version of Gregory’s categorization of types of illusion is developed, and a range of classic and more recent illusions that illustrate the differences between these philosophical viewpoints is considered in detail. Such cases make it clear that the discrepancies from the measurable image structure cannot be simply regarded as idiosyncrasies of sensory coding, but are categorical exemplars of perceptual illusions. The widespread existence of such illusory percepts is indicative of the evolutionary limits of adaptive sensory coding. (shrink)

We show that early vision can use monocular cues to rapidly complete partially-occluded objects. Visual search for easily detected fragments becomes difficult when the completed shape is similar to others in the display; conversely, search for fragments that are difficult to detect becomes easy when the completed shape is distinctive. Results indicate that completion occurs via the occlusion-triggered removal of occlusion edges and linking of associated regions. We fail to find evidence for a visible filling-in of contours or surfaces, but (...) do find evidence for a "functional" filling-in that prevents the constituent fragments from being rapidly accessed. As such, it is only the completed structures—and not the fragments themselves—that serve as the basis for rapid recognition. (shrink)

The idea that attention is necessary for consciousness (the “Necessity Thesis”) is frequently advocated by philosophers and psychologists alike. Experiments involving inattentional and change blindness are thought to support the Necessity Thesis, but they do so only if subjects failing to notice the target stimulus are also not conscious of it. This article uses commonsense phenomenological observations supplemented with empirical data to argue that some subjects failing to notice the target stimulus nonetheless experience its color. Since subjects not noticing the (...) target are commonly assumed to be not attending to it, these scenarios would be instances of consciousness without attention: instead of inattentional and change blindness supporting the Necessity Thesis, they would present counterexamples to it. (shrink)

Alva Noë’s _Action in Perception _offers a provocative and vigorous defense of the thesis that vision is enactive: visual experience depends on dispositional motor responses. On this view, vision and action are inextricably bound. In this review, I argue against enactive perception. I raise objections to seven lines of evidence that appear in Noë’s book, and I indicate some reasons for thinking that vision can operate independently of motor responses. I conclude that the relationship between vision and action is causal, (...) not constitutive. I then address three other contentious hypotheses in the book. Noë argues that visual states are not pictorial; he argues that all perception is conceptual; and he argues that the external world makes a constitutive contribution to experience. I am unpersuaded by these arguments, and I offer reasons to resist Noë’s conclusions. (shrink)

The paper proposes a way of bridging the gapbetween physical processes in the brain and the ''''felt''''aspect of sensory experience. The approach is based onthe idea that experience is not generated by brainprocesses themselves, but rather is constituted by theway these brain processes enable a particular form of''''give-and-take'''' between the perceiver and theenvironment. From this starting-point we are able tocharacterize the phenomenological differences betweenthe different sensory modalities in a more principledway than has been done in the past. We are also (...) ableto approach the issues of visual awareness andconsciousness in a satisfactory way. Finally weconsider a number of testable empirical consequences,one of which is the striking prediction of thephenomenon of ''''change blindness''''. (shrink)

An exploration is given of neural network features now being uncovered in cortical processing which begins to go a little way to help bridge the ''Explanatory Gap'' between phenomenal consciousness and correlated brain activity. A survey of properties suggested as being possessed by phenomenal consciousness leads to a set of criteria to be required of the correlated neural activity. Various neural styles of processing are reviewed and those fitting the criteria are selected for further analysis. One particular processing style, in (...) which semiautonomous and long-lasting cortical activity ''bubbles'' are created by input, is selected as being the most appropriate. Further experimental criteria are used to help narrow the possible neural styles involved. This leads to a class of neural models underpinning phenomenal consciousness and to a related set of testable predictions. (shrink)

The Global Workspace Theory and Information Integration Theory are two of the most currently accepted consciousness models; however, these models do not address many aspects of conscious experience. We compare these models to our previously proposed consciousness model in which the thalamus fills-in processed sensory information from corticothalamic feedback loops within a proposed 3D default space, resulting in the recreation of the internal and external worlds within the mind. This 3D default space is composed of all cells of the body, (...) which communicate via gap junctions and electrical potentials to create this unified space. We use 3D llustrations to explain how both visual and non-visual sensory information may be filled-in within this dynamic space, creating a unified seamless conscious experience. This neural sensory memory space is likely generated by baseline neural oscillatory activity from the default mode network, other salient networks, brainstem, and reticular activating system. (shrink)

Philosophers concerned with issues of mind have been turning to the neurosciences, especially neuropsychology, for empirical guidance. While I endorse this emphasis, I find that one important neuropsychological phenomenon, blindsight appears to have been misused by some prominent philosophers. In this paper, I examine this alleged misuse by spelling out the accounts of blindsight given by Daniel Dennett and Ned Block. I attempt to show that both Dennett and Block have ignored many complications surrounding blindsight including subjects' reports of visual (...) sensations. This neglect has serious ramifications for their respective models of human consciousness which I also try to explicate. Further, by misrepresenting blindsight, these accounts serve to hamper scientific and philosophical understanding of the phenomenon and of consciousness. I conclude by sketching a model of blindsight that acknowledges these neglected details. (shrink)

Dennett's "Consciousness Explained" (1991) is an inspiring but also a highly frustrating book. The line of the argument seems to be clear, but then at second sight it fades away. It turns out that Dennett uses six of the seven strategies which I discuss in my 'The Seven Strategies of the Sophisticated Pseudo-Scientist: A Look into Freud's Rhetorical Tool Box' (J. Gen. Phil. Sci., 2001) Discussing important examples of these strategies I show why "Consciousness Explained" is such a frustrating book. (...) As the examples used do not reflect minor problems but go to the heart of the matter and concern the book's main areas of contention, it turns out that, in spite of the valuable and insightful details, Dennett's materialistic view of consciousness is supported mainly by rhetorical sleights of hand. (shrink)

Philosophers concerned with issues of mind have been turning to the neurosciences, especially neuropsychology, for empirical guidance. While I endorse this emphasis, I find that one important neuropsychological phenomenon, blindsight appears to have been misused by some prominent philosophers. In this paper, I examine this alleged misuse by spelling out the accounts of blindsight given by Daniel Dennett and Ned Block. I attempt to show that both Dennett and Block have ignored many complications surrounding blindsight including subjects' reports of visual (...) sensations. This neglect has serious ramifications for their respective models of human consciousness which I also try to explicate. Further, by misrepresenting blindsight, these accounts serve to hamper scientific and philosophical understanding of the phenomenon and of consciousness. I conclude by sketching a model of blindsight that acknowledges these neglected details. (shrink)

Contour adaptation is a recently described paradigm that renders otherwise salient visual stimuli temporarily perceptually invisible. Here we investigate whether this illusion can be exploited to study visual awareness. We found that CA can induce seconds of sustained invisibility following similarly long periods of uninterrupted adaptation. Furthermore, even fragmented adaptors are capable of producing CA, with the strength of CA increasing monotonically as the adaptors encompass a greater fraction of the stimulus outline. However, different types of adaptor patterns, such as (...) distinctive shapes or illusory contours, produce equivalent levels of CA suggesting that the main determinants of CA are low-level stimulus characteristics, with minimal modulation by higher-order visual processes. Taken together, our results indicate that CA has desirable properties for studying visual awareness, including the production of prolonged periods of perceptual dissociation from stimulation as well as parametric dependencies of that dissociation on a host of stimulus parameters. (shrink)

The question of the constituting nature of colour is largely open. The old dispute between colour objectivism and colour subjectivism is still relevant. The former has defended itself against accusations of not being able to explain colour structures, while the latter view has received criticism for not being able to provide a plausible theory of the location of colours. By weakening the notion of physical categories, making some of them perceiver-depended, colour objectivists have managed to overcome at least some of (...) the previous accusations. However, the arguments based on Crane’s and Piantanida’s findings of the existence of binary colours like greenish-red and yellowish-blue, indicate the inadequacy of colour objectivism. Consequently, we have colours but our theories of them are false. (shrink)

Consciousness researchers are interested in distinguishing between mental activity that occurs with and without awareness . The inattentional blindness paradigm is an excellent tool for this question because it permits the independent manipulation of processing time and awareness. In the present study, we show that implicit texture segregation can occur during inattentional blindness, provided that the texture is exposed for a sufficient duration. In contrast, a Simon effect does not occur during inattentional blindness, even with similar exposure duration of the (...) critical stimulus. This reveals a dissociation between processing time and awareness, consistent with the possibility of separate processing streams for explicit and implicit visual perception. (shrink)

In Consciousness Explained Dan Dennett proposes a deflationary treatment of sensory qualia. He seeks to establish a continuity among both the neural and the conscious phenomena connected with the blind spot and with the perception of repetitive patterns on the one hand and the neutral and conscious phenomena connected with blindsight on the other. He aims to analyze the conscious phenomena associated with each in terms of what the brain ignores. Dennett offers a thought experiment about a blindsight patient who (...) has the sensory information that normals do, but who seems not to have their sensory qualia.What is it that normals know that this blindsight patient does not? Dennett′s answer is "nothing." Dennett′s denial of "filling-in" accounts of repetitive patterns and the blind spot constitute a Rylean intuition pump for this thought experiment. Research by Ramachandran raises important problems for Dennett′s account. Moreover, Dennett′s attempt to discount the significance of "artificial scotomas" inadvertently employs a principle that undermines his case for establishing the continuity between the phenomena in question. (shrink)

Dynamic surface completion is a phenomenon of visual filling-in where a colored pattern perceptually spreads onto an area confined by virtual contours in a multi-aperture motion display. The spreading effect is qualitatively similar to static texture spreading but widely surpasses it in strength, making it particularly suited for quantitative studies of visual interpolation processes. I carried out six experiments to establish with objective tasks that homogeneous color, as well as non-uniform texture spreading is a genuine representation of surface qualities and (...) thus goes beyond mere contour interpolation. The experiments also serve to relate the phenomena to ongoing discussions about potentially responsible mechanisms for spatiotemporal integration: With a phenomenological method, I examined to what extent simple sensory persistence might be causally involved in the effect under consideration. The findings are partially consistent with the idea of sensory persistence, and indicate that information fragments are integrated over a time window of about 100 to 150 ms to form a complete surface representation. (shrink)