Online research in philosophy

This commentary reviews and extends the target article's treatment of the topic of the role of acetylcholine in hallucinatory experience in health and disease. Particular attention is paid to differentiating muscarinic and nicotinic effects in modulating the use of virtual reality mechanisms by the brain. Then, attention is drawn to the similarities between these aspects of brain function and certain aspects of television digital compression technology.

This paper concentrates on the basic properties of ''consciousness'' that temporal coding is postulated to relate to. A description of phenomenal consciousness based on what introspection tells us about its contents is offered. This includes a consideration of the effect of various brain lesions that result in cortical blindness, apperceptive and associative agnosia, and blindsight, together with an account of the manner in which sight is regained after cortical injuries. I then discuss two therories of perception-Direct Realism and the Representative (...) Theory. This includes a discussion of the concept of the body-image, phantom limbs, the alleged projection of sensations, the ontological status of phenomenal space, the homunculus argument, the validity of topographic coding, the difference between the stimulus field and the visual field, and two theories of brain-mind relationship-the Identity Theory and the Bohr-Heisenberg theory of brain-mind complementarity. Finally I suggest that the binocular rivalry obtained in the case of the stroboscopic patterns that result from intermittent photic stimulation of one eye, when used in animal expeiments with unit recording, offers a good experimental method of investigating the binding problem. (shrink)

Current research on the neural basis of consciousness is based mainly on neuroimaging, physiology and psychophysics. This target article reviews what is known about biochemical factors that may contribute to the development of consciousness, based on loss of consciousness (i.e., coma). There are two theories of the biochemical mode of action of general anaesthetics. One is that anaesthesia is a direct (i.e., not receptor-mediated) effect of the anaesthetic on cellular neurophysiological function; the other is that some alteration of receptor function (...) occurs. General anaesthetics are mainly GABA agonists but some (such as ketamine) are glutamate antagonists. They also affect other systems, particularly cholinergic ones. There are various comas of metabolic origin. For example, a combination of small doses of the iron chelators desferrioxamine and prochlorperazine induce a profound and long lasting coma in humans. The mechanisms that might mediate this include redox mechanisms at the glutamate synapse, post-synaptic endocytosis of dopamine and iron, and intracellular iron-dopamine complexes, which are powerful dismuters of the superoxide anion. New findings in cell biology relating to endocytosis and recycling of receptors are discussed in a wider context. These biochemical events may induce coma by two mechanisms: (i) Consciousness may depend on widespread cortical (or cortico-thalamic) activation. (ii) Whereas these biochemical changes are widespread, only the changes in a subset of consciousness' neurons may count. An experimental program to distinguish between these two alternatives is proposed. (shrink)

We can in fact obtain scientific information about the contents of consciousness by the methods of introspectionist psychology. An example comes from the author's work on the stroboscopic patterns and from the way psychedelic drugs alter color perception.

There are currently two main philosophical theories of perception - Direct Realism and the Representative Theory. The former is supported by most contemporary philosophers, whereas the latter forms the groundwork for most scientific theories in this area. The paper describes a recent experiment involving retinal and cortical rivalry that provides strong empirical evidence that the Direct Realist theory is incorrect. There are of course a large number of related experiments on visual perception that would tend to lead us to the (...) same conclusion, but the experiment described in this paper does so in a singularly direct and straightforward manner. Often the most telling experiments are the simplest. (shrink)

This paper examines the impact that recent advances in clinical neurology, introspectionist psychology and neuroscience have upon the philosophical psycho?neural Identity Theory. Topics covered include (i) the nature and properties of phenomenal consciousness based on a study of the ?basic? visual field, i.e. that obtained in the complete dark, the Ganzfeld, and during recovery from occipital lobe injuries; (ii) the nature of the ?body?image? of neurology and its relation to the physical body; (iii) Descartes? error in choosing extension in space (...) as the criterion for distinguishing the physical and the mental; (iv) the technical distinction between sensing and perceiving; (v) why phenomenal Direct Realism is incorrect whereas epistemic DR and the representative theory are correct; (vi) the ontological and topological status of phenomenal space and physical space. This leads to considerations of the current ?binding problems? in neuroscience; the role of the brain mechanisms that construct the sensory fields of phenomenal consciousness; the ?homunculus? fallacy; the key difference between epistemic and non?epistemic perception as revealed by brain injury studies; and how the brain codes information, contrasting topological and vectorial coding, with particular reference to the binding problem. My conclusion is that the Identity Theory is incompatible with the scientific evidence from an integrated approach to modern introspectionist psychology, clinical neurology, and neuroscience. However, Cartesian Dualism is even more incompatible with the evidence. This leaves only two viable theories. The first is Bohr's theory of brain?consciousness complementarity. The second is the Broad?Price?Smythies theory of extension, which is a topological theory of the relation between phenomenal space and physical space. (shrink)

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