PLENARY PRESENTATIONS

ASSC4, as was the case with previous ASSC conferences, will again offer an outstanding plenary programme through which different perspectives on the unity of consciousness will be developed.

The plenary speakers listed below will each address this issue based on philosophical, neuropsychological, computational, and psychological approaches:

 

Rodney Cotterill	Physics Department, Technical University of Denmark	abstract
Zoltan Dienes	Department of Psychology, University of Sussex (UK)	abstract
Andreas Engel	Max-Planck-Institute for Brain Research, Frankfurt (Germany)	abstract
Glyn Humphreys	School of Psychology, University of Birmingham (UK)	abstract
Susan Hurley	Department of Philosophy, University of Warwick (UK)	abstract
Randall C. O'Reilly	Department of Psychology, University of Colorado (USA)	abstract
Pierre Perruchet	LEAD, Université de Bourgogne (France)	abstract
Sydney Shoemaker	Department of Philosophy, Cornell University (USA)	abstract
Catherine Tallon-Baudry	INSERM Unité 280 (France)	abstract
Giulio Tononi	The Neurosciences Institute, John Hopkins University (USA)	abstract
Anne Treisman	Department of Psychology, Princeton University (USA)	abstract
Andrew Young	Department of Psychology, University of York (UK)	abstract
Francisco Varela	LENA - Hôpital de la Salpétrière (France)	abstract
Semir Zeki	Institute of Cognitive Neuroscience, UCL (UK)	abstract

 

PL-01

Consciousness, Attention, and Binding Anne Treisman

The talk will discuss the relations between binding, attention and consciousness. Evidence that attention is required in order to bind features to form integrated objects includes the occurrence of illusory conjunctions when attention is overloaded or diverted, the binding deficit and the simultanagnosia that accompany bilateral parietal damage, the need for focused attention in search for unknown conjunctions, and the loss of local statistics on binding when attention is globally spread. Behavioral and fMRI studies of visual working memory suggest that new mechanisms are recruited when feature bindings must be explicitly remembered. According to feature integration theory, temporary "object files" are required to individuate and bind particular sets of features through their spatial locations. These form the visual substrate of what we consciously experience.  On the other hand there are indications that some implicit binding may be registered in the absence of any explicit awareness. Normal participants may show priming and learning of long-term conjunctions in automatization of visual search and in negative priming; recent studies of a Balints patient have shown interference from spatial information about which he is at chance in voluntary reports. One very speculative possibility is that attention carves out for conscious experience the correct subset of conjunctions amid the mass of potential combinations of the features present in the scene, but that the latter may indirectly affect either concurrent performance or future responses through lingering memory traces, as well as generating occasional conscious experiences of illusory bindings. Synchronized firing offers one possible neural account of both object files and the implicit priming and interference observed when attention is diverted.  Contact: Anne Treisman (treisman@princeton.edu) Princeton University  Department of Psychology  Princeton, NJ 08544-1010  U.S.A.

 

PL-02

Oscillatory synchrony as a signature for the unity of visual consciousness in humans Catherine Tallon-Baudry

As documented by many imaging studies, the perception of any visual object involves the activation of distinct, functionally specialized areas. How does a coherent percept emerge from this distributed network? We have examined the hypothesis that the neural representation of an object results from the oscillatory synchronization of the areas involved in its processing. We have now evidence in the human scalp EEG for the existence of induced oscillatory activities (e.g., with no fixed latency relationship with stimulus onset) in the beta (15-20Hz) and gamma (20-80 Hz) ranges, in different tasks involving the activation of an object representation. We have studied 1) a feature binding task (integration of attributes into a coherent object, perceived as a whole) 2) an hidden-object detection task (the subject had to activate the internal representation of the object searched for in order to pick it out from the picture) 3) a delayed-matching-to-sample task, in which the subject had to hold the sample representation active in short-term memory. In all these experiments, significant enhancements of induced oscillatory activity were observed, compared to a control stimulus or condition. In addition, the topography of the oscillations depended on the experiment, suggesting that they indeed reflected the synchronization of the areas specifically activated by the task.  The scalp-recorded oscillations are supposed to result from oscillatory synchronization at a large scale, encompassing several functional areas. Evidence favoring this hypothesis have been obtained in intra-cranial recordings in an epileptic patient: in a delayed-matching-to-sample task, different patterns of within- and between areas synchrony emerged during stimulus perception, and during its rehearsal in visual short-term memory. These patterns, involving the lateral occipital sulcus and the fusiform gyrus, were strongly influenced by the experimental conditions. It will be examined whether the degree of synchrony between areas could be a likely correlate of the level of awareness reached by the object. Contact: Catherine Tallon-Baudry (tallon-baudry@lyon151.inserm.fr) Mental Processes and Brain Activation Unit  INSERM Unite 280  151 Cours Albert Thomas  69003 Lyon  FRANCE

 

PL-03

Temporal binding and the neural correlates of consciousness Andreas K. Engel

Theories of binding, previously discussed with respect to perceptual integration, have recently advanced into the focus of the consciousness debate. A large body of neuropsychological and physiological evidence suggests that consciousness - in all of its various forms - has to be understood as a function of numerous interacting systems. Therefore, one of the key ingredients of any consciousness theory must be an account of how multiple component processes can be integrated and how large-scale coherence can emerge within distributed neural activity patterns. Furthermore, such a theory must specify mechanisms for the dynamic selection of subsets of neuronal responses, since only a fraction of all available information gains access to consciousness. I suggest that both requirements, cross-systems coherence and dynamic response selection, can be met by one and the same binding mechanism based on the synchronization of neuronal discharges. Recent evidence from animal studies supports this hypothesis, demonstrating that neuronal synchrony is related to perceptual integration, buildup of coherent representations, attentional selection, and awareness. These data suggest that synchronization, particularly if accompanied by fast oscillations in the gamma-frequency band, may be one of the necessary conditions for the emergence of conscious mental states. Contact: Andreas K. Engel (engel@mpih-frankfurt.mpg.de) Max-Planck-Institut fuer Hirnforschung  60528 Frankfurt  GERMANY

 

PL-04

Neural synchrony and Consciousness: Are we getting somewhere? Francisco Varela

The basic idea I will pursue in this presentation is that a cognitive 'self' can be conceived as a transient, dynamical signature of a largely distributed array of a multiplicity of brain regions and functions. Phase-locking synchrony appears as the best indicator of such complex process so far. I will present further support for this view with results obtained from awake human with multiple implanted electrodes studied over long periods of time, during the realization of complex cognitive tasks, and the transition to unconsciousness induced by anesthesia. The next question is whether such an integrated cognitive 'self ' can, in turn, be relate to consciousness in its strict first person or phenomenological sense. I will argue this view concerning the unity of a cognitive subject does better than traditional neural correlates of consciousness (NCCs) which searches for specific brain regions or neuronal traits. This is because a constantly re-emerging, unified cognitive subject provides a natural connection to directly incorporate first-person data as suggested by the neuro-phenomenological research project. I will conclude with recent results that encourage this line of inquiry. Contact: Francisco Varela (fv@ccr.jussieu.fr) LENA - Neurosciences Cognitives et Imagerie Cérébrale  Hôpital de la Salpètriere  47 Blvd. de l'Hôpital  75651 Paris cedex 13  FRANCE

 

PL-05

Consciousness Integrated and Differentiated Giulio Tononi

A useful way of identifying the neural basis of consciousness is to consider the kinds of neural processes that could account for its most fundamental properties. Two fundamental properties of consciousness are integration or unity, and differentiation or complexity. Integration is evident in that each conscious state is experienced as a whole and cannot be subdivided into independent components. Differentiation is evidenced by our ability to access, in a fraction of a second, any one out of countless numbers of conscious states. To understand these properties of consciousness and their neural substrates, a novel theory is developed that accounts at the same time for the integration and the differentiation of conscious experience. According to this theory, encapsulated in the dynamic core hypothesis, consciousness does not arise as a property of brain cells as such, but rather as a consequence of dynamic interactions of a continually changing functional cluster of nerve cells in the thalamus and cerebral cortex. The formulation of this theory has required the development of new theoretical concepts and measures, such as those for functional clustering and complexity, and the construction of large-scale computer models of brain function. A series of experiments using modern methods of magnetoencephalography has shown that neural correlates of conscious experience are consistent with the notion of a dynamic core and involve distributed brain areas which are different in different individuals. Contact: Giulio Tononi (tononi@nsi.edu) The Neurosciences Institute  10640 John Jay Hopkins Drive  San Diego, California 92121  U.S.A.

 

PL-06

How the Hippocampus and Prefrontal Cortex can Contribute to the Unity of Consciousness: A Computational Perspective Randall C. O'Reilly

Using computational neural network models, my colleagues and I have developed a theoretical framework for understanding the unique contributions of the hippocampus and prefrontal cortex to learning and memory. This framework has a number of implications for understanding the neural basis of the unity of conscious experience. Specifically, we think the hippocampus contributes to memory by rapidly and automatically binding together disparate cortical representations into a unitary representation Ñ this unitary representation can then be recalled by partial retrieval cues at a later time. Thus, it is the hippocampus that confers a sense of unity to a particular experience (i.e., an episodic memory) Ñ otherwise, these experiences would remain just a jumble of unconnected features and facts (e.g., location, people present, events that occurred, smells present). However, this hippocampal contribution is only evident in retrospective conscious experience Ñ our memories depend on hippocampal binding, but the unity of the present does not.  We think the prefrontal cortex is specialized for the ability to rapidly update and robustly maintain information in an active state (i.e., as patterns of neural firing). Computationally, this enables a form of activation-based processing that can be contrasted with the weight-based processing that the posterior cortex is more suited to perform. Prefrontally-mediated activation-based processing has two significant characteristics from a consciousness perspective: (a) actively-maintained representations provide a strong, dynamic influence on processing elsewhere in the system, leading to increased unity and coherence of processing; (b) the contents of activation-based processing are cognitively (consciously) accessible, whereas the knowledge underlying weight-based processing is embedded in the weights and is thus not accessible.  Computational models that motivate and illustrate these ideas will be presented, and broader role of computational modeling in the study of consciousness will be discussed. Contact: Randall C. O'Reilly (oreilly@grey.colorado.edu) Department of Psychology  Muenzinger D251C Campus Box 345  University of Colorado  Boulder, CO 80309-0345  U.S.A.

 

PL-07

Consciousness really explained? Rodney Cotterill

While this lecture is being given, the majority of the audience will be sitting quite motionless, at any instant. Yet everyone will be consciously attending to the speaker's words. Taken together, these facts seem to undermine the idea that consciousness is necessarily related to muscular movement. It will be argued nevertheless that consciousness does not develop exclusively in the cerebrum's sensory-processing areas (in conjunction with the thalamus), prior to signals possibly being dispatched to the motor-planning areas, as appears to be suggested by Crick and Koch (1995). Instead, it will be maintained that consciousness can prevail only if those motor-planning areas have already been activated. The presentation, which is also in sharp conflict with the multiple-microconsciousnesses idea of Zeki and Bartels (1999), will bolster the argument for its alternative mechanism by showing how this could have evolved from a basic design strategy present even in primitive organisms. And it will review supporting evidence from psychophysics and from mammalian physiology. By postulating that consciousness is inextricably tied to (possibly covert) self-paced probing of the environment, the overt version of which emerged as a behavioural trait four billion years ago, one can make mammalian neuroanatomy amenable to dramatically simple rationalisation, the roles of the cerebrum, thalamus, basal ganglia, cerebellum and hippocampus all becoming readily understandable. This alternative model even gives a strong hint as to the neural underpinnings of intelligence. Above all, the theory produces an attractively transparent explanation of the unity of conscious experience (Cotterill, 1998).   Cotterill, R.M.J. (1998). Enchanted Looms - Conscious Networks in Brains and Computers (Cambridge: Cambridge University Press). ISBN: 0-521-62435-5  Crick, F. & Koch, C. (1995). Are we aware of neural activity in primary visual cortex? Nature, 375, 121-123.  Zeki, S. & Bartels, A. (1999). Toward a theory of visual consciousness. Consciousness and Cognition, 8, 225-259.  Contact: Rodney Cotterill (firodcot@gbar.dtu.dk) Department of Physics  Technical University of Denmark  Building 307-309  DK-2800 Lyngby  DENMARK

 

PL-08

Fractionating the binding process Glyn W. Humphreys

I will present evidence from patients with visual agnosia and simultanagnosia that suggests that the binding process in vision can be fractionated into several isolatable processes. First I show that early processes involved in computing edge collinearity can be preserved in agnosia, though there can then be poor assignment of edges to shape. Thus a first stage of binding local elements into edges can be separated from a process of shape integration. Subsequently I show that binding by shape can fractionate from the binding of shape to surface detail, in a simultanagnosic patient. I suggest that shape binding can operate in the ventral visual system, whilst binding of shape and surface detail requires linkage through the dorsal visual stream, perhaps modulated by spatial attention. Contact: Glyn W. Humphreys (G.W.HUMPHREYS@Bham.ac.uk) The School of Psychology  University of Birmingham  Edgbaston  Birmingham B15 2TT  U.K.

 

PL-09

Overt and covert face recognition Andrew W. Young

One of the most intriguing revelations from research into the ways we perceive the world and access stored information about it is the finding, repeated across a number of areas, that, in addition to that which is consciously processed, information is picked up, stored and retrieved in ways that are variously described as implicit, covert or unconscious.  This phenomenon has also provoked attention from those interested in face recognition. It is a matter of common observation that recognition of a highly familiar face occurs more or less automatically - we cannot look at a familiar person and decide not to recognise them. Strikingly, some of these automatic aspects of face recognition seem to be preserved in cases of prosopagnosia, a severe defect of face recognition caused by brain injury. Covert recognition of familiar faces in prosopagnosia has now been demonstrated with a range of physiological and behavioural measures. Similar effects occur in neurologically normal individuals when stimuli are presented in such a way as to prevent their being consciously identified - like prosopagnosic patients, neurologically normal observers can show discriminative responses to faces they are not aware of having recognised.  Although such findings are now well-established, their correct interpretation remains a matter of debate. Contentious issues have included the relation between overt and covert recognition, the neurological pathways involved, and attempts to simulate the patterns of findings with computer models.  I will review these issues, and relate them to potentially important recent findings which have come from demonstrations that overt recognition can sometimes be achieved in prosopagnosia and from investigations of the basis of the Capgras delusion (the delusional belief that close relatives have been replaced by impostors) and its relation to prosopagnosia. Contact: Andrew W. Young (a.young@psych.york.ac.uk) Departement of Psychology  University of York  Heslington  York  YO10 5DD  U.K.

 

PL-10

The Disunity of Consciousness Semir Zeki

The most fundamental function of the visual brain is to acquire knowledge about the constant, essential properties of the visual world, in conditions in which the information reaching the brain is never constant from moment to moment. This requires the brain to undertake complex operations on the incoming visual signals, discounting all that is not essential for it to acquire knowledge about the world, selecting that which is important and subjecting the latter to operations that make the brain independent of the continually changing and non-essential information reaching it. One strategy that the brain uses in undertaking this task is that of functional specialization, through which different essential features, such as motion and colour, are extracted in specialized and geographically distinct visual areas lying outside the primary visual cortex area V1. Our recent psychophysical experiments show that, just as the processing systems for different attributes of vision are separate, such as colour, form and motion are perceived at different times, with colour leading motion by about 80 ms, thus leading to a perceptual asynchrony in terms of real time. The end-result of the operations in these individual areas is the acquisition of knowledge. But knowledge can only be acquired in the conscious state. A conscious awareness is therefore the corollary of activity in the specialized visual areas. Recent experiments using imaging and time resolution methods as well as patients blinded by lesions either in V1 or in more extensive parts of the visual cortex show that the activity in one or a small number of visual areas, without involvement of V1, can give rise to both conscious experience and a crude knowledge about the visual world. This leads us to the conclusion that consciousness itself may be modular.  The work of our laboratory is supported by the Wellcome Trust, London. Contact: Semir Zeki (s.zeki@ucl.ac.uk) University College London  Wellcome Department of Cognitive Neurology  Gower Street, London WC1E 6BT  U.K.

 

PL-11

Action and the Unity of Consciousness Susan Hurley

Can consciousness be only partially unified? This question cannot be addressed purely subjectively, in terms of 'what it is like' to be in conscious states. But how might it be answered in objective terms? Several neuropyschological examples will be examined and interpreted for what light they can shed on the possibility of partial unity. I argue that the possibility of partial unity cannot be settled by appeal to neuroanatomical isomorphism. However, the cases suggest how certain assumptions about the relationship of action to consciousness may make the attribution of partial unity attractive. Questioning these assumptions leads to a different, two-level approach to the unity of consciousness and its relation to action, in terms of normative coherence at the personal level and 'dynamic singularity' at the subpersonal level. Contact: Susan Hurley (s.l.hurley@warwick.ac.uk) Department of Philosophy  University of Warwick  Coventry CV4 7AL  U.K.

 

PL-12

Consciousness and co-consciousness Sydney Shoemaker

Let "consciousness atomism" be the view that the factors that go into making a mental state conscious are independent of those that constitute unity of consciousness, i.e., make different states co-conscious, and let "consciousness holism" be the view that denies this. Consciousness holism affirms, and consciousness atomism denies, that consciousness and co-consciousness are internally related -- that the factors that constitute them are inextricably intertwined.  Although seldom articulated, consciousness atomism is frequently taken for granted. Two current views of consciousness can seem to imply it. One is the view that a mental state's being conscious is its having phenomenal character, where this in turn is a matter of having properties of a certain sort -- "qualia." The other is the view which says that a state is conscious in virtue of its subject being conscious of it, where this in turn consists in its being accompanied by a "higher order thought" which ascribes it to the subject. But a state's having qualia cannot make a state conscious unless the subject is aware of the qualia, or at least unless they are introspectively accessible to the subject (as they are not in a case of blindsight, supposing there are qualia there at all). And a state's being accompanied by an appropriate higher-order thought will not make it conscious, and will not make the subject conscious of it, if both the state and the thought are insulated from the rest of the subject's mental life. So neither view is satisfactory unless supplemented with the requirement that the states in question are integrated with, stand in "access" relationships to, other states of the subject. And supplementing the views in this way involves abandoning consciousness atomism, since the integration and access relationships are an important part of what constitutes the unity of consciousness. This is one way in which consciousness and unity consciousness are internally related.  Consciousness and the unity of consciousness are internally related in another way. Perceptual experiences, which are paradigmatically conscious, are of things that are either temporally extended (e.g., a melody, or a spoken sentence) or spatially extended (written sentences, ordinary physical objects, entire landscapes). Such experiences have parts corresponding to the temporal or spatial parts of what they represent, and these must be so related that together they represent relations between the parts they represent. And this requires that they be co-conscious. The very existence of such conscious mental states requires unity of consciousness. But the specification of this sort of unity of consciousness is precisely a specification of what it takes to make such states conscious, and more generally what it takes for a person to perceive spatial and temporal relations between different things. And this, in turn, involves the considerations that go into constituting the sort of unity of consciousness considered earlier, specifically the co-consciousness of perceptual experiences with other mental states. Contact: Sydney Shoemaker (ss56@cornell.edu) Sage School of Philosophy  Cornell University  218 Goldwin Smith Hall  Ithaca  New York 14853-3201  U.S.A.

 

PL-13

Unifying consciousness with explicit knowledge Zoltan Dienes

In this talk I will establish what it is for something to be implicit or explicit. The approach to implicit knowledge is taken from Dienes and Perner (1999), which relates the implicit-explicit distinction to knowledge representations. What it is for a representation to represent something implicitly or explicitly is defined and those concepts are applied to knowledge. Next I will show how maximally explicit knowledge is naturally associated with consciousness, how some degree of explicitness is needed for voluntary control and thus how increasing explicitness is associated with increasing metacognitive abilities. I will argue that fully explicit knowledge should be associated with a sense of being part of a unified consciousness, both because of the explicit representation of the subject of the mental experience and because explicit knowledge can be represented as knowledge and hence as coherent (or incoherent) with respect to other knowledge. New evidence indicating the extent of people's implicit or explicit knowledge in an implicit learning paradigm will then be presented. This evidence will indicate people can be consistently correct in dealing with a context-free grammar while lacking any knowledge that they have knowledge. The relation of this to unity in consciousness will be discussed. Contact: Zoltan Dienes (dienes@biols.susx.ac.uk) University of Sussex  Brighton BN1 9QG  ENGLAND  U.K.

 

PL-14

Thinking Learning Differently: The Self-Organizing Consciousness (SOC) Model Pierre Perruchet & Annie Vinter

In the prevalent conceptions of learning, whether based on symbolic or connectionist architectures, most if not all of the information manipulation and computation involved during a training episode takes place at an unconscious level. The function assigned to consciousness consists in making the end-product of these computations accessible. This access is thought of as an epiphenomenon, or at best as allowing the high-level control of certain operations or actions.  Starting from an alternative, "mentalistic" (e.g. Dulany, 1991; Searle, 1992) view, we propose the hypothesis that the content of phenomenal consciousness is the very stuff on which unconscious associative processes operate. This hypothesis explains why conscious percepts and representations become increasingly isomorphic with the world structure. Indeed, when ubiquitous principles of associative memory and learning (such as unit strengthening through repetition, or disappearance in the absence of reinforcement) are applied to the content of consciousness, this content self-organizes as a consequence of repeated exposure to a structured environment. This is simply because associative learning processes tend to bind together the features of the world that co-occur, and the features of the world that co-occur have a high chance of belonging to the same world units. This self-organizing property which, in the most simple cases, has been demonstrated by means of computational modeling, may be tentatively generalized to very complex situations if we admit a few additional, but psychologically plausible, assumptions. After generalization, this conception accounts for important phenomena involved in human development and learning, without the necessity of postulating any sophisticated unconscious learning system.  Given this view, the unity of consciousness is no longer conceived of simply as a phenomenon that requires explanation, but instead itself becomes an explanatory concept. Our proposal is that binding together the various components of phenomenal experience is a necessary and sufficient condition for the occurrence of associative learning. Recent empirical data on the role of attention in learning provide strong support for this proposal. The unified field of experience resulting from this integration is certainly of importance in terms of the immediate adaptive function of any internal representation of the world. However, when considered within a dynamical perspective, it is itself the condition for an improvement of the representativity of conscious contents in subsequent occasions. Although this view is presented here in connection with cold aspects of cognition, such as visual and auditory representations, it is worth mentioning that entering the rich content of phenomenal experience into a causal schema of learning opens the path for the integration of emotional and motivational aspects of human life into future developments of this framework. Contact: Pierre Perruchet (perruche@u-bourgogne.fr) LEAD  Faculte des Sciences  Universite de Bourgogne  6 Bd. Gabriel  21000 Dijon  FRANCE

Overview

Submission

Registration

Travel Info

Programme

Complete URL to this document:  http://www.assc.caltech.edu/assc4/prog/plenaries.html  Last updated 11 May 2000 by Axel Cleeremans