Online research in philosophy

The foundation of phenomenological image theories is the view that image perception leads to a perception sui generis . In order to grasp this peculiarity of image perception, two ways have traditionally been considered: either through a description of the particular object of image perception or through a description of the unique origin of image perception. This article explores a third way within the phenomenology of the image by trying to determine the uniqueness of image perception through its peculiar, necessary effects on the observer of the image. The thesis is: The observer of an image does not become an image object in the image. It is only in the case of image perception that there is relief through a gap in participation. It is the perception of something without the demand, as the perceiving person, of being physically involved in what is perceived.

The psychological concept of illusion is defined as a process involving an interaction of logical and empirical considerations. Common usage suggests that an illusion is a discrepancy between one's awareness and some stimulus. Following preliminary definitions of classes of stimuli, five definitions of illusion are considered, based upon the possible discrepancies between awareness and a stimulus. It is found that each of these definitions fails to make important distinctions, even to the point of equating all illusory and perceptual phenomena. This dilemma is resolved by redefining illusion without reference to truth or falsity, but relative to the functioning of a given perceptual system under different conditions. The definition accepted as best is 'a discrepancy between one's perceptions of an object or event observed under different conditions'. Conditions may differ in terms of stimulus exposure, stimulus context, or experiental context. The philosophical and psychological implications are discussed of accepting a definition of illusion not based on a discrepancy between awareness and a stimulus.

The book I review, _Sleights of Mind_, aims to illuminate properties of perceptual systems by discussing human susceptibility to magical illusions. I describe how the authors use psychological principles to explain two tricks, spoon bending and the Miser's Dream. I also argue that the book is congenial to the following view of illusions: susceptibility to illusion is the result of evolutionary trade-offs; perceptual systems must make assumptions in order to function at all, but susceptibility to illusion is the byproduct of such assumptions.

If one formulates Helmholtz's ideas about perception in terms of modern-day theories one arrives at a model of perceptual inference and learning that can explain a remarkable range of neurobiological facts. Using constructs from statistical physics it can be shown that the problems of inferring what cause our sensory inputs and learning causal regularities in the sensorium can be resolved using exactly the same principles. Furthermore, inference and learning can proceed in a biologically plausible fashion. The ensuing scheme rests on Empirical Bayes and hierarchical models of how sensory information is generated. The use of hierarchical models enables the brain to construct prior expectations in a dynamic and context-sensitive fashion. This scheme provides a principled way to understand many aspects of the brain's organisation and responses. In this paper, we suggest that these perceptual processes are just one emergent property of systems that conform to a free-energy principle. The free-energy considered here represents a bound on the surprise inherent in any exchange with the environment, under expectations encoded by its state or configuration. A system can minimise free-energy by changing its configuration to change the way it samples the environment, or to change its expectations. These changes correspond to action and perception, respectively, and lead to an adaptive exchange with the environment that is characteristic of biological systems. This treatment implies that the system's state and structure encode an implicit and probabilistic model of the environment. We will look at models entailed by the brain and how minimisation of free-energy can explain its dynamics and structure.

Seeing, Doing, and Knowing is an original and comprehensive philosophical treatment of sense perception as it is currently investigated by cognitive neuroscientists. Its central theme is the task-oriented specialization of sensory systems across the biological domain; these systems coevolve with an organism's learning and action systems, providing the latter with classifications of external objects in terms of sensory categories purpose--built for their need. On the basis of this central idea, Matthen presents novel theories of perceptual similarity, content, and realism. His work will be a stimulating resource for a wide range of scholars and students across philosophy and psychology.

Neural impulses from the senses to the brain convey information, not sensation. The direct electrical stimulation of the cortex produces sensations. Hence, such sensations are evoked in the brain, and not received from the senses, nor from the outside world through the senses. More specifically, the experience of light is evoked in the brain and not received from the eyes. Consequently, the born blind, too, would experience light in response to electrical brain stimulation. The luminosity of light is not a property of electromagnetic radiation. If the experience of light is private, then so are the visual observations it makes possible.

Cross-modal perceptual illusions occur when a stimulus to one modality impacts perceptual experience associated with another modality. Unlike synaesthesia, cross-modal illusions are intelligible as results of perceptual strategies for dealing with sensory stimulation to multiple modalities, rather than as mere quirks. I argue that understanding cross-modal illusions reveals an important flaw in a widespread conception of the senses, and of their role in perceptual experience, according to which understanding perception and perceptual experience is a matter of assembling independently viable stories about vision, audition, olfaction, and the rest.