Gray extrapolates from circuit models of psychopathology to propose neural substrates for the contents of consciousness. I raise three concerns: knowledge of synaptic arrangements may be inadequate to fully support his model; latent inhibition deficits in schizophrenia, a focus of this and related models, are complex and deserve replication; and this conjecture omits discussion of the neuropsychological basis for the contents of the unconscious.

An active role for conscious processes in the production of behaviour is proposed, involving top level controls in a hierarchy of behavioural control. It is suggested that by inhibiting or sensitizing lower levels in the hierarchy conscious processes can play a role in the organization of ongoing behaviour. Conscious control can be more or less evident, according to prevailing circumstances.

This is a bibliography of books and articles on consciousness in philosophy, cognitive science, and neuroscience over the last 30 years. There are three main sections, devoted to monographs, edited collections of papers, and articles. The first two of these sections are each divided into three subsections containing books in each of the main areas of research. The third section is divided into 12 subsections, with 10 subject headings for philosophical articles along with two additional subsections for articles in cognitive (...) science and neuroscience. Of course the division is somewhat arbitrary, but I hope that it makes the bibliography easier to use. This bibliography has first been compiled by Thomas Metzinger and David Chalmers to appear in print in two philosophical anthologies on conscious experience . From 1995 onwards it has been continuously updated by Thomas Metzinger, and now is freely available as a PDF-, RTF-, or HTML-file. This bibliography mainly attempts to cover the Anglo-Saxon and German debates, in a non-annotated, fully formatted way that makes it easy to "cut and paste" from the original file. To a certain degree this bibliography also contains items in other languages than English and German - all submissions in other languages are welcome. Last update of current version: July 13th, 2001. (shrink)

P/A (Block's phenomenal/access) confounds a logical distinction with an empirical claim. Success of P/A in its logical role has almost no bearing on its plausibility as an empirical thesis (i.e., that two kinds of consciousness exist). The advantage of P/A over a single-consciousness assumption is unclear, but one of Block's analogies for P (liquid in a hydraulic computer) may be used to clarify the notion of consciousness as cognitive “hardware.”.

An extended examination of Libet's works led to a comprehensive reinterpretation of his results. According to this reinterpretation, the Minimum Train Duration of electrical brain stimulation should be considered as the time needed to create a brain stimulus efficient for producing conscious sensation and not as a basis for inferring the latency for conscious sensation of peripheral origin. Latency for conscious sensation with brain stimulation may occurafterthe Minimum Train Duration. Backward masking with cortical stimuli suggests a 125-300 ms minimum value (...) for the latency for conscious sensation of threshold skin stimuli. Backward enhancement is not suitable for inferring this latency. For determining temporal relations between stimuli that correspond to subjects' reports, theendof cerebral Minimum Train Duration should be used as reference, rather than its onset. Results of coupling peripheral and cortical stimuli are explained by a latency after the cortical Minimum Train Duration, having roughly the same duration as the latency for supraliminal skin stimuli. Results of coupling peripheral stimuli and stimuli to medial lemniscus (LM) are explained by a shorter LM latency and/or a longer peripheral latency. This interpretation suggests a 230 ms minimum value for the latency for conscious sensation of somatosensory near-threshold stimuli. The backward referral hypothesis, as formulated by Libet, should not be retained. Long readiness potentials preceding spontaneous conscious or nonconscious movements suggest that both kinds of movement are nonconsciously initiated. The validity of Libet's measures of W and M moments (Libet et al., 1983a) is questionable due to problems involving latencies, training, and introspective distinction of W and M. Veto of intended actions may be initially nonconscious but dependent on conscious awareness. (shrink)

1. Introduction The readiness potential was found to precede voluntary acts by about half a second or more (Kornhuber & Deecke, 1965). Kornhuber (1984) discussed the readiness potential in terms of volition, arguing that it is not the manifestation of an attentional processes. Libet discussed it in relation to consciousness and to free will (Libet et al. 1983a; 1983b; Libet, 1985, 1992, 1993). Libet asked the following questions. Are voluntary acts initiated by a conscious decision to act? Are the physiological (...) facts compatible with the belief that free will determines our voluntary acts? What is the role of consciousness in voluntary action? In this paper I will discuss these questions and the answers that Libet gave to them. (shrink)

How does the brain generate our experience of being in control over our actions and their effects? Here, we argue that the perception of events as self-caused emerges from a comparison between anticipated and actual action-effects: if the representation of an event that follows an action is activated before the action, the event is experienced as caused by one’s own action, whereas in the case of a mismatch it will be attributed to an external cause rather than to the self. (...) In a subliminal priming paradigm we show that participants overestimated how much control they had over objectively uncontrollable stimuli, which appeared after free- or forced-choice actions, when a masked prime activated a representation of the stimuli immediately before each action. This prime-induced control-illusion was independent from whether primes were consciously perceived. Results indicate that the conscious experience of control is modulated by unconscious anticipations of action-effects. (shrink)

In the April 2002 edition of JCS I outlined the conscious electromagnetic information field theory, claiming that consciousness is that component of the brain's electromagnetic field that is downloaded to motor neurons and is thereby capable of communicating its informational content to the outside world. In this paper I demonstrate that the theory is robust to criticisms. I further explore implications of the theory particularly as regards the relationship between electromagnetic fields, information, the phenomenology of consciousness and the meaning of (...) free will. Using cemi field theory I propose a working hypothesis that shows, among other things, that awareness and information represent the same phenomenon viewed from different reference frames. (shrink)

*[[This paper appears in _Toward a Science of Consciousness II: The Second Tucson Discussions and Debates_ (S. Hameroff, A. Kaszniak, and A.Scott, eds), published with MIT Press in 1998. It is a transcript of my talk at the second Tucson conference in April 1996, lightly edited to include the contents of overheads and to exclude some diversions with a consciousness meter. A more in-depth argument for some of the claims in this paper can be found in Chapter 6 of my (...) book _The Conscious Mind_ (Chalmers, 1996). ]]. (shrink)

Drawing on previous models of anxiety, intermediate memory, the positive symptoms of schizophrenia, and goal-directed behaviour, a neuropsychological hypothesis is proposed for the generation of the contents of consciousness. It is suggested that these correspond to the outputs of a comparator that, on a moment-by-moment basis, compares the current state of the organism's perceptual world with a predicted state. An outline is given of the information-processing functions of the comparator system and of the neural systems which mediate them. The hypothesis (...) appears to be able to account for a number of key features of the contents of consciousness. However, it is argued that neitherthis nor any existing comparable hypothesis is yet able to explain why the brain should generate conscious experience of any kind at all. (shrink)

I have taken an experimental approach to this question. Freely voluntary acts are preceded by a specific electrical change in the brain that begins 550 ms before the act. Human subjects became aware of intention to act 350-400 ms after RP starts, but 200 ms. before the motor act. The volitional process is therefore initiated unconsciously. But the conscious function could still control the outcome; it can veto the act. Free will is therefore not excluded. These findings put constraints on (...) views of how free will may operate; it would not initiate a voluntary act but it could control performance of the act. The findings also affect views of guilt and responsibility. But the deeper question still remains: Are freely voluntary acts subject to macro-deterministic laws or can they appear without such constraints, non-determined by natural laws and ‘truly free'? I shall present an experimentalist view about these fundamental philosophical opposites. (shrink)

To make progress on the problem of consciousness, we have to confront it directly. In this paper, I first isolate the truly hard part of the problem, separating it from more tractable parts and giving an account of why it is so difficult to explain. I critique some recent work that uses reductive methods to address consciousness, and argue that such methods inevitably fail to come to grips with the hardest part of the problem. Once this failure is recognized, the (...) door to further progress is opened. In the second half of the paper, I argue that if we move to a new kind of nonreductive explanation, a naturalistic account of consciousness can be given. I put forward my own candidate for such an account: a nonreductive theory based on principles of structural coherence and organizational invariance, and a double-aspect theory of information. (shrink)

The rise of Artificial Intelligence (AI) has produced prophets and prophecies announcing that the age of artificial consciousness is near. Not only does the mere idea that any machine could ever possess the full potential of human consciousness suggest that AI could replace the role of God in the future, it also puts into question the fundamental human right to freedom and dignity. This position paper takes the stand that, in the light of all we currently know about brain evolution (...) and the never-stopping formation of adaptive neural circuitry for learning, memory, decision making and, ultimately, fully conscious reasoning and creativity in the human species, the idea of an artificial consciousness appears misconceived. The paper highlights some of the major reasons why. While awareness to external stimuli for processes such as perception, recognition, and operational problem solving is under the direct control of functionally specific brain networks associated with sensory and cognitive functions across animal species, consciousness is a unique property of the human mind. (shrink)

Consciousness is known to be limited in processing capacity and often described in terms of a unique processing stream across a single dimension: time. In this paper, we discuss a purely temporal pattern code, functionally decoupled from spatial signals, for conscious state generation in the brain. Arguments in favour of such a code include Dehaene et al.'s long-distance reverberation postulate, Ramachandran's remapping hypothesis, evidence for a temporal coherence index and coincidence detectors, and Grossberg's Adaptive Resonance Theory. A time-bin resonance model (...) is developed, where temporal signatures of conscious states are generated on the basis of signal reverberation across large distances in highly plastic neural circuits. The temporal signatures are delivered by neural activity patterns which, beyond a certain statistical threshold, activate, maintain, and terminate a conscious brain state like a bar code would activate, maintain, or inactivate the electronic locks of a safe. Such temporal resonance would reflect a higher level of neural processing, independent from sensorial or perceptual brain mechanisms. (shrink)

The mind-body problem is analyzed in a physicalist perspective. By combining the concepts of emergence and algorithmic information theory in a thought experiment employing a basic nonlinear process, it is shown that epistemically strongly emergent properties may develop in a physical system. Turning to the significantly more complex neural network of the brain it is subsequently argued that consciousness is epistemically emergent. Thus reductionist understanding of consciousness appears not possible; the mind-body problem does not have a reductionist solution. The ontologically (...) emergent character of consciousness is then identified from a combinatorial analysis relating to universal limits set by quantum mechanics, implying that consciousness is fundamentally irreducible to low-level phenomena. (shrink)

In Gray's conjecture, mismatches in the subicular comparator and matches have equal prominence in consciousness. In rival cognitive views novelty and difficulty especially elicit more conscious modes of cognition and higher levels of self-regulation. The mismatch between Gray's conjecture and these views is discussed.

Gray has expanded his account of schizophrenia to explain consciousness as well. His theory explains neither phenomenon adequately because he treats individual minds in isolation. The primary function of consciousness is to permit high level interactions with other conscious beings. The key symptoms of schizophrenia reflect a failure of this mechanism.

Gray's neuropsychological model of consciousness uses a hierarchical feedback loop framework that has been extensively discussed by many others in psychology. This commentary therefore urges Gray to integrate with, or at least acknowledge previous models. It also points out flaws in his feedback model and suggests directions for further theoretical work.

P-Consciousness is to be understood in terms of an immediate fluctuating continuum that is a presentation of raw experiential matter against which A-consciousness acts to objectify, impose form or make determinate “thinkable” contents. A representationalises P but P is not itself representational, at least in terms of some concepts of “representation.” Block's arguments fall short of establishing that P is representational and, given the sort of cognitive science assumptions he is working with, he is unable to account for the aspect (...) of phenomenal content that he thinks goes beyond “representational” content. BBS discussion reveals the need for greater analysis and justification for a representationalist thesis of P. (shrink)

The thesis that animals feel a morally relevant kind of pain is an incredibly popular one, but explaining the evidence for this belief is surprisingly challenging. Michael Murray has defended neo-Cartesianism, the view that animals may lack the ability to feel pain in a morally relevant sense. In this paper, I present the reasons for doubting that animals feel morally relevant pain. I then respond to critics of Murray’s position, arguing that the evidence proposed more recently is still largely unpersuasive. (...) I end by considering the implications for moral discourse and praxis. (shrink)

Because consciousness has an organizational, or functional, center, Gray supposes that there must be a corresponding physical center in the brain. He proposes further that since this center generates consciousness, ablating it would eliminate consciousness, while leaving behavior intact. But the center of consciousness is simply the product of the functional linkages among sensory input, memory, inner speech, and so on, and behavior.

As Gray insists, his comparator model proposes a brute correlation only – of consciousness with septohippocampal output. I suggest that the comparator straddles a feedback loop that boosts the activation ofnovelrepresentations, thus helping them feature in present or recollected experience. Such a role in organizing conscious contents would transcend correlation and help explain how consciousness emerges from brain function.

Gray mistakenly thinks I have rejected the sort of theoretical enterprise he is undertaking, because, according to him, I think that "more data" is all that is needed to resolve all the issues. Not at all. My stalking horse was the bizarre (often pathetic) claim that no amount of empirical, "third-person point-of-view" science (data plus theory) could ever reduce the residue of mystery about consciousness to zero. This "New Mysterianism" (Flanagan, 1991) is one that he should want to combat as (...) vigorously as I have done. (shrink)

Libet discovered that a substantial duration (> 0.5-1.0 s) of direct electrical stimulation of the surface of the somatosensory cortex at threshold currents is required before human subjects can report that a conscious somatosensory experience had occurred. Using a reaction time method we confirm that a similarly long stimulation duration at threshold currents is required for activation of elementary visual experiences (phosphenes) in human subjects following stimulation of the surface of the striate cortex. However, the reaction times for the subject (...) to respond to the cessation of the visual experience after the end of electrical stimulation could be as brief as 225-242 ms. We also carried out extensive studies in cats under a variety of anesthetic conditions using the same electrodes and parameters of stimulation employed in the human studies to study the patterns of neuronal activity beneath the stimulating surface electrode. Whereas sufficiently strong currents can activate neurons within milliseconds, stimulating currents close to threshold activate sustained neural activity only after at least 350-500 ms. When currents are close to threshold, some neurons are inhibited for several hundreds of millisecond before the balance between inhibition and excitation shifts towards excitation. These results suggest that the prolonged latencies, i.e., latencies beyond 200-250 ms, for the emergence of conscious experience following direct cortical stimulation result from a delay in the sustained activation of underlying cortical neurons at threshold currents rather than being due to any unusually long duration in central processing time. Intracellular records from cortical neurological cells during repetitive electrical stimulation of the surface of the feline striate cortex demonstrate that such stimulation induces a profound depolarizing shift in membrane potential that may persist after each stimulus train. Such a depolarization is evidence that extracellular K+ concentrations have increased during electrical stimulation. Such an increase in extracellular K+ progressively increases cortical excitability until the threshold for sustained activation of cortical neurons is reached and then exceeded. Consequently, the long latency for threshold activation of cortical neurons depends upon a dynamically increasing cortical facilatory process that begins hundreds of milliseconds before there is sustained activation of such neurons. In some cases, this facilatory process must overcome an initial stimulus-induced inhibition before neuronal firing commences. (shrink)

This paper is an edited transcription of a talk at the 1997 Montreal symposium on "Consciousness at the Frontiers of Neuroscience". There's not much here that isn't said elsewhere, e.g. in "Facing Up to the Problem of Consciousness" and "How Can We Construct a Science of Consciousness?"]].

Gray's account is remarkable in its depth and scope but too little attention is paid to poor correspondences with the literature on hippocampal/subicular damage, the theta rhythm, and novelty detection. An alternative account, focusing on hippocampal involvement in organizing memories in a way that makes them accessible to conscious recollection but not in access to consciousness per se, avoids each of these limitations.

Gray takes an information-processing paradigm as his departure point, invoking a comparator as part of the system. He concludes that consciousness is to be found “in” the comparator but is unable to point to how the comparison takes place. Thus, the comparator turns out not to be an entity arising out of brain research per se, but out of the logic of the paradigm. In this way, Gray both reinvents dualism and remains trapped in the language game of his own (...) model – ending up dealing with the unknowable. (shrink)

In this commentary, I point out some weaknesses in Gray's target article and, in the light of that discussion, I attempt to delineate the kinds of problem a cognitive neuroscience of consciousness faces on its way to a scientific understanding of subjective experience.

Gray hypothesizes that the contents of consciousness correspond to the outputs of a subicular (hippocampal/temporal lobe) comparator that compares the current state of the organism's perceptual world with a predicted state. I argue that Gray has identified a key contributing system to conscious awareness, but that his model is inadequate for explaining how conscious contents are generated in the brain. An alternative model is offered.

The distinction between phenomenal and access consciousness arises from the battle between biological and computational approaches to the mind. If P = A, the computationalists are right; but if not, the biological nature of P yields its scientific nature.

Segmentalized consciousness in schizophrenia reflects a loss of the normal Gestalt organization and contextualization of perception. Grays model explains such segmentalization in terms of septohippocampal dysfunction, which is consistent with known neuropsychological impairment in schizophrenia. However, other considerations suggest that everyday perception and its failure in schizophrenia also involve prefrontal executive mechanisms, which are only minimally elaborated by Gray.

This commentary is divided into two parts. The first considers a possible role for Gray's predictor plus comparator mechanism in human episodic recognition memory. It draws on the computational specifications of recognition outlined in Humphreys et al. to demonstrate how the logically necessary components of recognition tasks might be mapped onto the mechanism. The second part demonstrates how the mechanism outlined by Gray might be implicated in a form of imitative learning suitable for the acquisition of complex tasks.

Perspective and reflection have each been considered in some way basic to phenomenal consciousness. Each has possible evolutionary value, though neither seems sufficient for consciousness. Consider an account of consciousness in terms of the combination of perspective and reflection, its relationship to the problem of other minds, and its capacity to inherit evolutionary explanation from its components.

The psychological literature about consciousness has been analyzed. It is argued that: 1) Only the higher symbolic cognitive powers like the ability to keep secrets, knowledge of self or self-consciousness, a long-term view on the future, the ability to determine long-term goals, and to freely plan future behavior, add positive fitness-value to consciousness. Without these higher intellectual abilities consciousness will have only negative fitness value and no positive one. The intellectual powers mentioned may therefore be considered as prerequisites for consciousness. (...) Consciousness may therefore only be expected in those animal species that show these capacities in their behavior. So far these capacities have only been described for the anthropoid apes and humans. For the time being, they are therefore the only species in which consciousness may be expected. (shrink)

The critical reinterpretations of Libet's research by G. Gomes make speculative, unwarranted, and untested assumptions. These assumptions and arguments are analyzed and their status relative to Libet's findings is criticized.

Various neurophysiological experiments have revealed remarkable correlations between cortical neuronal activity and subjective experiences. However, the mere presence of neuronal electrical activity does not appear to be sufficient to produce these experiences. It has been suggested that the explanation for the neural basis of consciousness might lie in understanding the reason that some types of neuronal activity possess subjective correlates and others do not. Here I propose and develop the idea that this difference may be caused by the existence of (...) an elementary nonarbitrary linkage between temporal or spatiotemporal patterns of neuronal activity and their subjective attributes. I also show how cortical neural circuits capable of generating experience-coding patterns could emerge during evolution and brain development, due to the presence of spontaneous stochastic neuronal activity and activity-dependent synaptic plasticity. This hypothesis leads to several testable predictions, principal among which is the idea that the neural correlates of consciousness are essentially innate and universal. (shrink)

While substantial progress has been made in the field known as artificial consciousness, at the present time there is no generally accepted phenomenally conscious machine, nor even a clear route to how one might be produced should we decide to try. Here, we take the position that, from our computer science perspective, a major reason for this is a computational explanatory gap: our inability to understand/explain the implementation of high-level cognitive algorithms in terms of neurocomputational processing. We explain how addressing (...) the computational explanatory gap can identify computational correlates of consciousness. We suggest that bridging this gap is not only critical to further progress in the area of machine consciousness, but would also inform the search for neurobiological correlates of consciousness and would, with high probability, contribute to demystifying the “hard problem” of understanding the mind–brain relationship. We compile a listing of previously proposed computational correlates of consciousness and, based on the results of recent computational modeling, suggest that the gating mechanisms associated with top-down cognitive control of working memory should be added to this list. We conclude that developing neurocognitive architectures that contribute to bridging the computational explanatory gap provides a credible and achievable roadmap to understanding the ultimate prospects for a conscious machine, and to a better understanding of the mind–brain problem in general. (shrink)

If sensations were behaviorally conceived, as they should be, as complex functional patterns of interaction between overt behavior and the environment, there would be no point in searching for them as instantaneous psychic elements within the brain or as internal products of the brain.

To avoid teleological interpretations, it is important to make a distinction between functions and uses of consciousness, and to address questions concerning the consequences of consciousness. Assumptions about the phylogenetic distribution of consciousness are examined. It is concluded that there is some value in identifying consciousness an exclusively human attribute.

Gray unwisely melds together two distinguishable contributions of consciousness: one to epistemology, the other to evolution. He also renders consciousness needlessly invisible behaviorally.

The communicative aspects of the contents of consciousness are analyzed in the framework of a neural network model of animal communication. We discuss some issues raised by Gray, such as the control of the contents of consciousness, the adaptive value of consciousness, conscious and unconscious behaviors, and the nature of a model's consciousness.

Robust theories concerning the connection between consciousness and brain function should derive not only from empirical evidence but also from a well grounded inind-body ontology. In the case of the comparator hypothesis, Gray develops his ideas relying extensively on empirical evidence, but he bounces irresolutely among logically incompatible metaphysical theses which, in turn, leads him to excessively skeptical conclusions concerning the naturalization of consciousness.

The commentary argues that we cannot be sure that human consciousness has survival value and that in order to understand the origins and, perhaps, the function of consciousness, we should examine the behavioural and neural precursors to consciousness in nonhumans. An example is given of research on the role of context in decisions regarding fleeing from probable predators in the Mongolian gerbil.

Libet demonstrated that a substantial duration (>0.5-1.0 s) of direct electrical stimulation of the surface of a sensory cortex at a threshold or liminal current is required before a subject can experience a percept. Libet and his co-workers originally proposed that the result could be due either to spatial and temporal facilitation of the underlying neurons or additionally to a prolonged central processing time. However, over the next four decades, Libet chose to attribute the prolonged latency for evoking conscious experience (...) to a prolonged central processing time. In my view, Libet has not provided any convincing evidence, either on the basis of his own past work or in his critique of my paper, for his hypothesis of a central processing time exceeding 0.5s before conscious experience emerges following direct electrical threshold stimulation of the cortical surface. I stand by my original results and conclusion that such prolonged latencies are largely the consequence of a dynamically increasing cortical facilitatory process that begins hundreds of milliseconds before there is a sustained neuronal activation. In some cases, the facilitatory process must overcome an initial stimulus-induced inhibition before neuronal firing commences. (shrink)

The comparator model is insufficient for three reasons. First, consciousness is involved in the process of comparison as well as in the output. Second, we still do not have enough neurophysiological information to match the events of consciousness, although such knowledge is growing. Third, the anatomical localisation proposed can be damaged bilaterally but consciousness will persist.

Gray, like other recent authors, seeks a scientific approach to consciousness, but fails to provide a biologically convincing description, partly because he implicitly bases his model on a computationalist foundation that embeds the contents of thought in irreducible symbolic representations. When patterns of neural activity instantiating conscious thought are shorn of homuncular observers, it appears most likely that these patterns and the circuitry that compares them with memories and plans should be found distributed over large regions of neocortex.

Gray's comparator model fails to provide an adequate explanation of consciousness for two reasons. First, it is based on a narrow definition of consciousness that excludes basic phenomenology and active functions of consciousness. Second, match/mismatch decisions can be made without producing an experience of consciousness. The model thus violates the sufficiency criterion.