Towards solving the hard problem of consciousness: The varieties of brain resonances and the conscious experiences that they support

Reviews

The Equations for Consciousness: A Reply to “Tracking the Travels,” a Review of <i>Journey of the Mind</i>

EDITORIAL article Front. Psychol., 01 September 2011 | https://doi.org/10.3389/fpsyg.2011.00191

Although subjective conscious experience and introspection have long been considered unscientific and banned from psychology, they are indispensable in scientific practice. These terms are used in scientific contexts today; however, their meaning remains vague, and earlier objections to the distinction between conscious experience and unconscious processing, remain valid. This also applies to the distinction between conscious visual perception and unconscious visual processing. Damage to the geniculo-striate pathway or the visual cortex results in a perimetrically blind visual hemifield contralateral to the damaged hemisphere. In some cases, cerebral blindness is not absolute. Patients may still be able to guess the presence, location, shape or direction of movement of a stimulus even though they report no conscious visual experience. This “unconscious” ability was termed “blindsight”. The present paper demonstrates how the term conscious visual experience can be introduced in a logically precise and methodologically correct way and becomes amenable to scientific examination. The distinction between conscious experience and unconscious processing is demonstrated in the cases of conscious vision and blindsight. The literature on “blindsight” and its neurobiological basis is reviewed. It is shown that blindsight can be caused by residual functions of neural networks of the visual cortex that have survived cerebral damage, and may also be due to an extrastriate pathway via the midbrain to cortical areas such as areas V4 and MT/V5.

Theories of consciousness using neurobiological data or being influenced by these data have been focused either on states of consciousness or contents of consciousness. These theories have occasionally used evidence from psychophysical phenomena where conscious experience is a dependent experimental variable. However, systematic catalog of many such relevant phenomena has not been offered in terms of these theories. In the perceptual retouch theory of thalamocortical interaction, recently developed to become a blend with the dendritic integration theory, consciousness states and contents of consciousness are explained by the same mechanism. This general-purpose mechanism has modulation of the cortical layer-5 pyramidal neurons that represent contents of consciousness as its core. As a surplus, many experimental psychophysical phenomena of conscious perception can be explained by the workings of this mechanism. Historical origins and current views inherent in this theory are presented and reviewed.

The problem of consciousness is mostly regarded as identical to the mind-body problem. According to Chalmers’ philosophical arguments, the hard problem of consciousness lies in establishing and explaining the link between physical processes and conscious experiences, via psychological processes. A brief history of various theories of consciousness is given and a selection of theories are tested against Zeman’s three fundamental intuitions and Chalmers’ controversial zombie argument. The hard problem of consciousness is further described using Levine’s notion of an explanatory gap between physical matter and conscious experience, through the first and third persons. Various states, contents, levels and processes of consciousness are summarised, including Damasio and Meyer’s dual perspective for defining consciousness. Tart’s three definitions do not entirely describe altered states of consciousness. While the challenge of finding the core function of human and animal sleep remains unknown when tested under the null hypothesis, studies on the neural correlates of consciousness during meditation have revealed neuroplasticity effects. The synchrony of gamma brain oscillations reflecting various styles of meditation or attention, also known as the binding problem, may be related to conscious experiences. This binding problem with gamma brain oscillatory synchronization also arises in relation to sensory awareness or perception, affecting the perception of time and hallucinatory experiences in various disorders of consciousness such as severe schizophrenic and deja vu (in healthy or epileptic) patients. In conjunction with medication treatments, music therapy is often useful in accelerating the healing process in most such disorders of consciousness. It is still unknown how this sensory awareness to music is perceived in medicated patients suffering from disorders of consciousness. More clinically elusive are near death experiences, in which consciousness persists independently of brain function, where there is no scientific basis for such consciousness to exist and no physiological or psychological model that can explain it. Near death experiences can be regarded as a special state of consciousness, which provides further evidence that the consciousness problem may be very close to the mind-body problem that originates in Descartes’ classic theory of dualism and is transformed into Chalmers’ contemporary theory of natural dualism. The final section of this chapter offers an overview of all invited chapters.

The processes whereby our brains continue to learn about a changing world in a stable fashion throughout life are proposed to lead to conscious experiences. These processes include the learning of top-down expectations, the matching of these expectations against bottom-up data, the focusing of attention upon the expected clusters of information, and the development of resonant states between bottom-up and top-down processes as they reach a predictive and attentive consensus between what is expected and what is there in the outside world. It is suggested that all conscious states in the brain are resonant states, and that these resonant states trigger learning of sensory and cognitive representations when they amplify and synchronize distributed neural signals that are bound by the resonance. Thus, processes of learning, intention, attention, synchronization, and consciousness are intimately bound up together. The name Adaptive Resonance Theory, or ART, summarizes the predicted link between these processes. Illustrative psychophysical and neurobiological data have been explained and quantitatively simulated using these concepts in the areas of early vision, visual object recognition, auditory streaming, and speech perception, among others. It is noted how these mechanisms seem to be realized by known laminar circuits of the visual cortex. In particular, they seem to be operative at all levels of the visual system. Indeed, the mammalian neocortex, which is the seat of higher biological intelligence in all modalities, exhibits a remarkably uniform laminar architecture, with six characteristic layers and sublamina. These known laminar ART, or LAMINART, models illustrate the emerging paradigm of Laminar Computing which is attempting to answer the fundamental question: How does laminar computing give rise to biological intelligence? These laminar circuits also illustrate the fact that, in a rapidly growing number of examples, an individual model can quantitatively simulate the recorded dynamics of identified neurons in anatomically characterized circuits and the behaviors that they control. In this precise sense, the classical Mind/Body problem is starting to get solved. It is further noted that many parallel processing streams of the brain often compute properties that are complementary to each other, much as a lock fits a key or the pieces of a puzzle fit together. Hierarchical and parallel interactions within and between these processing streams can overcome their complementary deficiencies by generating emergent properties that compute complete information about a prescribed form of intelligent behavior. This emerging paradigm of Complementary Computing is proposed to be a better paradigm for understanding biological intelligence than various previous proposals, such as the postulate of independent modules that are specialized to carry out prescribed intelligent tasks. Complementary computing is illustrated by the fact that sensory and cognitive processing in the What processing stream of the brain, that passes through cortical areas V1-V2-V4-IT on the way to prefrontal cortex, obey top-down matching and learning laws that are often complementary to those used for spatial and motor processing in the brain’s Where/How processing stream, that passes through cortical areas V1-MT-MST-PPC on the way to prefrontal cortex. These complementary properties enable sensory and cognitive representations to maintain their stability as we learn more about the world, while allowing spatial and motor representations to forget learned maps and gains that are no longer appropriate as our bodies develop and grow from infanthood to adulthood. Procedural memories are proposed to be unconscious because the inhibitory matching process that supports their spatial and motor processes cannot lead to resonance. Because ART principles and mechanisms clarify how incremental learning can occur autonomously without a loss of stability under both unsupervised and supervised conditions in response to a rapidly changing world, algorithms based on ART have been used in a wide range of applications in science and technology.

Consciousness or conscious experience is a mental phenomenon that is familiar to all of us, but the way in which it is produced escapes us to a large extent. Each person has a vague idea of what it means to be conscious, but consciousness is rather hard to define, albeit easy to identify. It is that function of the brain that makes us conscious of external or internal stimuli and of our thoughts regarding these subjective experiences. Conscious experience is a first-person perspective of mental states and events tracking as they unfold. It includes mental phenomena such as a perception, emotion, memory, idea, continuous temporal sequence of events. A mental process and its adjoining neurophysiological phenomena represent two aspects of the same event. We have direct access to the mental aspect, while we can observe the neurophysiological aspect only when we study the event as a biological process. The psychological study of consciousness describes the special properties of this brain function, its origin and utility in the global economy of an animal organism. The neurobiological study aims to find the neural correlates of consciousness, aims to establish causal relations between the neural phenomena and the different conscious states. Lastly, the formulation of an explanatory theory can provide a satisfactory understanding of the phenomenon. This review aims to bring some clarification in the field of consciousness, selecting the hypotheses which mostly fulfill the requirements, in order to be confirmed as explanatory theories. A valuable test for confirming an explanatory hypothesis is its predictive power. Using this criterion we have evaluated comparatively, some of the proposed explaining hypotheses.

Consciousness CLEARS the mind

Multiple Perspectives on Consciousness for Cognitive Science Richard A. Carlson (racarlson@psu.edu) Department of Psychology, Penn State University 613 Moore Building, University Park, PA 16802 USA The huge contemporary literature on consciousness spans multiple disciplines, including psychology, philosophy, and neuroscience. This tutorial will introduce participants to major proposals about consciousness, and their empirical and methodological implications. The goal is to prepare participants to explore the consciousness literature in greater depth. Our consideration of perspectives on consciousness will be organized by considering how these perspectives address core questions about consciousness, including: (a) How can subjectivity and agency be accommodated in a scientific theory of consciousness? (b) How can conscious and nonconscious or unconscious processes and representations be systematically distinguished? (c) How can conscious mental states be assessed or measured? (d) How can dissociations and impairments of consciousness be understood? The literatures to be considered address these questions in analytic, functional, computational, and implementational terms. Philosophical Perspectives Philosophers approach the problem of consciousness from a variety of analytic perspectives, some focusing on contemporary formulations of the mind-body problem and others on analyses of subjective experience. Among the philosophical perspectives we will consider are John Searle’s (1992) analysis of consciousness in terms of intentionality, David Chalmer’s (1996) distinction between “easy” and “hard” problems of consciousness, David Rosenthal’s (1993) “higher order thought” proposal, and Daniel Dennett’s (1991) “multiple drafts” theory of consciousness. Neuroscience Perspectives Neuroscientists have made a wide variety of proposals concerning the neural correlates of consciousness (NCC). A starting assumption is that a subset of current neural activity is correlated with current conscious experience. There is controversy, however, concerning how that subset is to be identified. For example, the NCC might be limited to particular types of cells or anatomical structures, or comprise global patterns of synchronized neural activity. We will consider recent proposals concerning NCC by Crick and Koch (1998), Damasio (2000), and Edelman and Tononi Psychological Perspectives Psychological perspectives on consciousness generally focus on functionally-defined aspects of cognition. For example, psychologists have identified consciousness with working memory (Baars, 1988), attention (Schneider & Pimm-Smith, 1997), metacognition (Nelson, 1996), and with the structure of mental states (Carlson, 1997). Cognitive research often focuses on distinguishing conscious and nonconscious influences on psychological processes such as learning (Dienes & Berry, 1997) and perception (Merikle, Smilek, & Eastwood, 2001). This research has generated a rich literature on methods for assessing consciousness. References Baars, B. J. (1988). A cognitive theory of consciousness. New York: Cambridge University Press. Carlson, R. A. (1997). Experienced Cognition. Mahwah, NJ: Lawrence Erlbaum Associates. Chalmers, D. (1996). The conscious mind. Oxford: Oxford University Press. Crick, F., & Koch, C. (1998). Consciousness and neuroscience. Cerebral Cortex, 8, 97-107. Damasio, A. R. (2000). A neurobiology for consciousness. In T. Metzinger (Ed.), Neural correlates of consciousness Cambridge, MA: The MIT Press. Dienes, Z., & Berry, D. (1997). Implicit learning: Below the subjective threshold. Psychonomic Bulletin and Review, 4, Dennett, D. C. (1991). Consciousness explained. Boston: Little, Brown and Company. Edelman, G. M., & Tononi, G. (2000). Reentry and the dynamic core: Neural correlates of conscious experience. In T. Metzinger (Ed.), Neural correlates of consciousness. Cambridge, MA: The MIT Press. Merikle, P. M., Smilek, D., & Eastwood, J. D. (2001). Perception without awareness: perspectives from cognitive psychology. Cognition, 79, 115-134. Nelson, T. O. (1996). Consciousness and metacognition. American Psychologist, 51, 102-116. Rosenthal, D. M. (1993). Thinking that one thinks. In M. Davies, & G. W. Humphreys (Eds.), Consciousness: Psychological and philosophical essays. Oxford: Blackwell. Searle, J. R. (1992). The rediscovery of the mind. Cambridge, MA: The MIT Press. Schneider, W., & Pimm-Smith, M. (1997). Consciousness as a message aware control mechanism to modulate cognitive processing. J. Cohen, & J. Schooler (Eds.), Scientific approaches to consciousness: The 25th Carnegie Symposium on Cognition. Mahwah, NJ: Erlbaum.

How consciousness arises from brain activity has been a topic of intense scientific research for decades. But how does one identify the neural basis of something that is intrinsically personal and subjective? A hallmark approach has been to ask human observers to judge stimuli as 'seen' (conscious) and 'unseen' (unconscious) and use post hoc sorting of neural measurements based these judgments. Unfortunately, cognitive and response biases are known to strongly affect how observers place their criterion for judging stimuli as 'seen' versus 'unseen', thereby confounding neural measures of consciousness. Surprisingly however, the effect of conservative and liberal criterion placement on neural measures of unconscious and conscious processing has never been explicitly investigated. Here, we use simulations and electrophysiological brain measurements to show that conservative criterion placement has an unintuitive consequence: rather than selectively providing a cautious estimate of conscious processing, it inflates effect sizes in neural measures of both conscious and unconscious processing, while liberal criterion placement does the reverse. After showing this in simulation, we performed decoding analyses on two electroencephalography studies that employ common subjective indicators of conscious awareness, in which we experimentally manipulated the response criterion. The results confirm that the predicted confounding effects of criterion placement on neural measures of unconscious and conscious processing occur in empirical data, while further showing that the most widely used subjective scale, the Perceptual Awareness Scale (PAS), does not guard against criterion confounds. Follow-up simulations explicate how the experimental context determines whether the relative confounding effect of criterion placement is larger in neural measures of either conscious or unconscious processing. We conclude that criterion placement threatens the construct validity of neural measures of conscious and unconscious processing.

How consciousness arises from brain activity has been a topic of intense scientific research for decades. But how does one identify the neural basis of something that is intrinsically personal and subjective? A hallmark approach has been to ask human observers to judge stimuli as ‘seen’ (conscious) and ‘unseen’ (unconscious) and use post hoc sorting of neural measurements based these judgments. Unfortunately, cognitive and response biases are known to strongly affect how observers place their criterion for judging stimuli as ‘seen’ versus ‘unseen’, thereby confounding neural measures of consciousness. Surprisingly however, the effect of conservative and liberal criterion placement on neural measures of unconscious and conscious processing has never been explicitly investigated. Here, we use simulations and electrophysiological brain measurements to show that conservative criterion placement has an unintuitive consequence: rather than selectively providing a cautious estimate of conscious processing, it inflates effect sizes in neural measures of both conscious and unconscious processing, while liberal criterion placement does the reverse. After showing this in simulation, we performed decoding analyses on two electroencephalography studies that employ common subjective indicators of conscious awareness, in which we experimentally manipulated the response criterion. The results confirm that the predicted confounding effects of criterion placement on neural measures of unconscious and conscious processing occur in empirical data, while further showing that the most widely used subjective scale, the Perceptual Awareness Scale (PAS), does not guard against criterion confounds. Follow-up simulations explicate how the experimental context determines whether the relative confounding effect of criterion placement is larger in neural measures of either conscious or unconscious processing. We conclude that criterion placement threatens the construct validity of neural measures of conscious and unconscious processing.

How consciousness arises from brain activity has been a topic of intense scientific research for decades. But how does one identify the neural basis of something that is intrinsically personal and subjective? A hallmark approach has been to ask human observers to judge stimuli as ‘seen’ (conscious) and ‘unseen’ (unconscious) and use post hoc sorting of neural measurements based these judgments. Unfortunately, cognitive and response biases are known to strongly affect how observers place their criterion for judging stimuli as ‘seen’ versus ‘unseen’, thereby confounding neural measures of consciousness. Surprisingly however, the effect of conservative and liberal criterion placement on neural measures of unconscious and conscious processing has never been explicitly investigated. Here, we use simulations and electrophysiological brain measurements to show that conservative criterion placement has an unintuitive consequence: rather than selectively providing a cautious estimate of conscious processing, it inflates effect sizes in neural measures of both conscious and unconscious processing, while liberal criterion placement does the reverse. After showing this in simulation, we performed decoding analyses on two electroencephalography studies that employ common subjective indicators of conscious awareness, in which we experimentally manipulated the response criterion. The results confirm that the predicted confounding effects of criterion placement on neural measures of unconscious and conscious processing occur in empirical data, while further showing that the most widely used subjective scale, the Perceptual Awareness Scale (PAS), does not guard against criterion confounds. Follow-up simulations explicate how the experimental context determines whether the relative confounding effect of criterion placement is larger in neural measures of either conscious or unconscious processing. We conclude that criterion placement threatens the construct validity of neural measures of conscious and unconscious processing.

How consciousness arises from brain activity has been a topic of intense scientific research for decades. But how does one identify the neural basis of something that is intrinsically personal and subjective? A hallmark approach has been to ask observers to judge stimuli as ‘seen’ (conscious) and ‘unseen’ (unconscious) and use post hoc sorting of neural measurements based these judgments. Unfortunately, cognitive and response biases are known to strongly affect how observers place their criterion for judging stimuli as ‘seen’ vs. ‘unseen’, thereby confounding neural measures of consciousness. Surprisingly however, the effect of conservative and liberal criterion placement on neural measures of unconscious and conscious processing has never been explicitly investigated. Here we use simulations and electrophysiological brain measurements to show that conservative criterion placement has an unintuitive consequence: rather than selectively providing a cautious estimate of conscious processing, it inflates effect sizes in neural measures of both conscious and unconscious processing, while liberal criterion placement does the reverse. After showing this in simulation, we performed decoding analyses on two electroencephalography studies that employ common subjective indicators of conscious awareness, in which we experimentally manipulated the response criterion. The results confirm that the predicted confounding effects of criterion placement on neural measures of unconscious and conscious processing occur in empirical data, while further showing that the most widely used subjective scale, the Perceptual Awareness Scale (PAS), does not guard against criterion confounds. Follow-up simulations explicate how the experimental context determines whether the relative confounding effect of criterion placement is larger in neural measures of either conscious or unconscious processing. We conclude that criterion placement threatens the construct validity of neural measures of conscious and unconscious processing.

How consciousness arises from brain activity has been a topic of intense scientific research for decades. But how does one identify the neural basis of something that is intrinsically personal and subjective? A hallmark approach has been to ask observers to judge stimuli as ‘seen’ (conscious) and ‘unseen’ (unconscious) and use post hoc sorting of neural measurements based these judgments. Unfortunately, cognitive and response biases are known to strongly affect how observers place their criterion for judging stimuli as ’seen’ vs. ’unseen’, thereby confounding neural measures of consciousness. Surprisingly however, the effect of conservative and liberal criterion placement on neural measures of unconscious and conscious processing has never been explicitly investigated. Here we use simulations and electrophysiological brain measurements to show that conservative criterion placement has an unintuitive consequence: rather than selectively providing a cautious estimate of conscious processing, it inflates effect sizes in neural measures of both conscious and unconscious processing, while liberal criterion placement does the reverse. After showing this in simulation, we performed decoding analyses on two electroencephalography studies that employ common subjective indicators of conscious awareness, in which we experimentally manipulated the response criterion. The results confirm that the predicted confounding effects of criterion placement on neural measures of unconscious and conscious processing occur in empirical data, while further showing that the most widely used subjective scale, the Perceptual Awareness Scale (PAS), does not guard against criterion confounds. Follow-up simulations explicate how the experimental context determines whether the relative confounding effect of criterion placement is larger in neural measures of either conscious or unconscious processing. We conclude that criterion placement threatens the construct validity of neural measures of conscious and unconscious processing.