Most ?theories of consciousness? are based on vague speculations about the properties of conscious experience. We aim to provide a more solid basis for a science of consciousness. We argue that a theory of consciousness should provide an account of the very processes that allow us to acquire and use information about our own mental states ? the processes underlying introspection. This can be achieved through the construction of information processing models that can account for ?Type-C? processes. Type-C processes can (...) be specified experimentally by identifying paradigms in which awareness of the stimulus is necessary for an intentional action. The Shallice (1988b) framework is put forward as providing an initial account of Type-C processes, which can relate perceptual consciousness to consciously performed actions. Further, we suggest that this framework may be refined through the investigation of the functions of prefrontal cortex. The formulation of our approach requires us to consider fundamental conceptual and methodological issues associated with consciousness. The most significant of these issues concerns the scientific use of introspective evidence. We outline and justify a conservative methodological approach to the use of introspective evidence, with attention to the difficulties historically associated with its use in psychology. (shrink)

The standard behavioral index for human consciousness is the ability to report events with accuracy. While this method is routinely used for scientific and medical applications in humans, it is not easy to generalize to other species. Brain evidence may lend itself more easily to comparative testing. Human consciousness involves widespread, relatively fast low-amplitude interactions in the thalamocortical core of the brain, driven by current tasks and conditions. These features have also been found in other mammals, which suggests that consciousness (...) is a major biological adaptation in mammals. We suggest more than a dozen additional properties of human consciousness that may be used to test comparative predictions. Such homologies are necessarily more remote in non-mammals, which do not share the thalamocortical complex. However, as we learn more we may be able to make “deeper” predictions that apply to some birds, reptiles, large-brained invertebrates, and perhaps other species. (shrink)

Traditional explanations of multistable visual phenomena (e.g. ambiguous figures, perceptual rivalry) suggest that the basis for spontaneous reversals in perception lies in antagonistic connectivity within the visual system. In this review, we suggest an alternative, albeit speculative, explanation for visual multistability – that spontaneous alternations reflect responses to active, programmed events initiated by brain areas that integrate sensory and non-sensory information to coordinate a diversity of behaviors. Much evidence suggests that perceptual reversals are themselves more closely related to the expression (...) of a behavior than to passive sensory responses: (1) they are initiated spontaneously, often voluntarily, and are influenced by subjective variables such as attention and mood; (2) the alternation process is greatly facilitated with practice and compromised by lesions in non-visual cortical areas; (3) the alternation process has temporal dynamics similar to those of spontaneously initiated behaviors; (4) functional imaging reveals that brain areas associated with a variety of cognitive behaviors are specifically activated when vision becomes unstable. In this scheme, reorganizations of activity throughout the visual cortex, concurrent with perceptual reversals, are initiated by higher, largely non-sensory brain centers. Such direct intervention in the processing of the sensory input by brain structures associated with planning and motor programming might serve an important role in perceptual organization, particularly in aspects related to selective attention. (shrink)

I argue that informational models of consciousness, including those proposed by the Integrated Information Theory, don’t presuppose or entail any particular view about the physical or metaphysical nature of consciousness. Such models only tell us how certain properties of consciousness can be mathematically described, thus providing a quantitative characterization of the phenomenon of consciousness that may contribute to the development of new methods of assessment and guide the explanatory project by supplying additional constraints on theoretical proposals. While informational models are (...) in principle compatible with multiple physical interpretations, a preliminary argument in favour of the continuity between informational approaches and the mechanistic project in neuroscience can be made based on historical precedents. (shrink)

Fronto-parietal activity has been frequently observed in fMRI and PET studies of attention, working memory, and episodic memory retrieval. Several recent fMRI studies have also reported fronto-parietal activity during conscious visual perception. A major goal of this review was to assess the degree of anatomical overlap among activation patterns associated with these four functions. A second goal was to shed light on the possible cognitive relationship of processes that relate to common brain activity across functions. For all reviewed functions we (...) observed a consistent and overlapping pattern of brain activity. The overlap was most pronounced for the bilateral parietal cortex , and dorsolateral prefrontal cortex . The common fronto-parietal activity will be discussed in terms of processes related to integration of distributed representations in the brain. (shrink)

Correspondence should be addressed to David A. Leopold [email protected] the viewing of certain patterns, widely known as ambiguous or puzzle figures, perception lapses into a sequence of spontaneous alternations, switching every few seconds between two or more visual interpretations of the stimulus. Although their nature and origin remain topics of debate, these stochastic switches are generally thought to be the automatic and inevitable consequence of viewing a pattern without a unique solution. We report here that in humans such perceptual alternations (...) can be slowed, and even brought to a standstill, if the visual stimulus is periodically removed from view. We also show, with a visual illusion, that this stabilizing effect hinges on perceptual disappearance rather than on actual removal of the stimulus. These findings indicate that uninterrupted subjective perception of an ambiguous pattern is required for the initiation of the brain-state changes underlying multistable vision.Visual perception involves coordination between sensory sampling of the world and active interpretation of the sensory data. Human perception of objects and scenes is normally stable and robust, but it falters when one is presented with patterns that are inherently ambiguous or contradictory. Under such conditions, vision lapses into a chain of continually alternating percepts, whereby a viable visual interpretation dominates for a few seconds and is then replaced by a rival interpretation. This multistable vision, or 'multistability', is thought to result from destabilization of fundamental visual mechanisms, and has offered valuable insights into how sensory patterns are actively organized and interpreted in the brain1, 2. Despite a great deal of recent research and interest in multistable perception, however, its neurophysiological underpinnings remain poorly understood. Physiological studies have suggested that disambiguation of ambiguous patterns. (shrink)

Binocular rivalry provides a useful situation for studying the relation between the temporal flow of conscious experience and the temporal dynamics of neural activity. After proposing a phenomenological framework for understanding temporal aspects of consciousness, we review experimental research on multistable perception and binocular rivalry, singling out various methodological, theoretical, and empirical aspects of this research relevant to studying the flow of experience. We then review an experimental study from our group explicitly concerned with relating the temporal dynamics of rivalrous (...) experience to the temporal dynamics of cortical activity. Drawing attention to the importance of dealing with ongoing activity and its inherent changing nature at both phenomenological and neurodynamical levels, we argue that the notions of recurrence and variability are pertinent to understanding rivalry in particular and the flow of experience in general. (shrink)

The neural basis of binocular rivalry has beenthe subject of vigorous debate. Do discrepantmonocular patterns rival for awareness becauseof neural competition among patternrepresentations or monocular channels? In thisarticle, I briefly review psychophysical andneurophysiological evidence pertaining to boththeories and discuss important new neuroimagingdata which reveal that rivalry is fullyresolved in monocular visual cortex. These newfindings strongly suggest that interocularcompetition mediates binocular rivalry and thatV1 plays an important role in the selection ofconscious visual information. They furthersuggest that rivalry is not a unitaryphenomenon. (...) Interocular competition may fullyaccount for binocular rivalry whereas aseparate mechanism involving patterncompetition likely accounts for monocular andstimulus rivalry. (shrink)

Research into the neural correlates of consciousness (NCCs) has blossomed, due to the advent of new and increasingly sophisticated brain research tools. Neuroimaging has uncovered a variety of brain processes that relate to conscious perception, obtained in a range of experimental paradigms. But methods such as functional magnetic resonance imaging or electroencephalography do not always afford inference on the functional role these brain processes play in conscious vision. Such empirical NCCs could reflect neural prerequisites, neural consequences, or neural substrates of (...) a conscious experience. Here, we take a closer look at the use of non-invasive brain stimulation (NIBS) techniques in this context. We discuss and review how NIBS methodology can enlighten our understanding of brain mechanisms underlying conscious vision by disentangling the empirical NCCs. (shrink)

Logothetis, N.K.: Single units and conscious vision. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 353, 1801-1818 (1998) Abstract.

Physiological studies of binocular rivalry have provided important clues to the relationship between neural activity in the brain and visual awareness.However, uncertainty about these insights has been raised by a recent study showing that the events underlying binocular rivalry occur earlier in the visual pathway than was previously thought.

Aftereffects induced by invisible stimuli constitute a powerful tool to investigate what type of neural information processing can occur in the absence of visual awareness. This approach has been successfully used to demonstrate that awareness of oriented gratings or translating stimuli is not necessary to obtain a robust orientation-specific or motion-specific aftereffect. We exploit motion-induced blindness to investigate the related question of the influence of visual awareness on the formation of negative afterimages. Our results show that MIB does not affect (...) the persistence and intensity of afterimages. Thus, there is no significant contribution to the formation of afterimages beyond the sites mediating MIB. (shrink)

Recent experiments have shown that the amplitudes of cortical gamma band oscillatory activities that occur during anesthesia are often greater than amplitudes of similar activities that occur without anesthesia. This result is apparently at odds with the hypothesis that synchronized oscillatory activities constitute the neural correlate of consciousness. We argue that while synchronization and oscillatory patterning are necessary conditions for consciousness, they are not sufficient. Based on the results of a binocular rivalry study of Fries et al. (1997), we propose (...) that the degrees of oscillatory strength and synchronization of neuronal activities determine the degree of awareness those activities produce. On the other hand, the overal firing rates of neurons in cortical sensory areas are not correlated with the degree of awareness the activities of those neurons produce. The results of the experiment of Fries et al. (1997) appear to conflict with the results of another binocular rivalry experiment, in which monkeys were trained to pull a lever in order to report which stimulus object was being perceived (Leopold & Logothetis, 1996). In the latter experiment, it was demonstrated that the firing rates of neurons in striate cortex did not change during perceptual alterations, while 90% of neurons in inferior and superior temporal cortices changed their firing rate when the perceived image changed. This result led to the conclusion that activities in temporal cortex are correlated with visual awareness, but those in striate cortex are not. We argue that activities in temporal cortex contribute little, if anything, to perceptual awareness, and that their primary function is computational. Thus the correlation between the firing rates of neurons in these areas and the responses of the monkeys is due to the recognition of a particular stimulus object, which in turn is due to the computations made there. (shrink)

It is now conventional wisdom that conscious experience — or in Nagel’s canonical characterization, “what it is like to be” for an organism — is what makes the mind-body problem so intractable. By the same token, our current conceptions of the mind-body relation are inadequate and some conceptual development is urgently needed. Our overall aim in this paper is to make some progress towards that conceptual development. We first examine a currently neglected, yet fundamental aspect of consciousness. This aspect is (...) the spontaneity of consciousness, by which we mean its inner plasticity and inner purposiveness. We then sketch a “neurophenomenological” framework for thinking about the relationship between the spontaneity of consciousness and dynamic patterns of brain activity as studied in cognitive neuroscience. We conclude by proposing that the conscious mentality of sentient organisms or animals is active and dynamic, and that this “enactive” conception of consciousness can help us to move beyond the classical dichotomy between materialism and dualism. (shrink)

Process aspects are prevalent in many domains of reality, and consciousness is no exception. Nevertheless, while the processual approach implicitly underlies the theories of consciousness, an explicit statement of the question is scarcely found in the literature. This paper tries to bridge this gap. Here, I argue that conscious experience fulfils all the requirements for a processual analysis: it is complex, functionally/causally determined, and has a temporal basis. Then, I revisit an old concept, self-transformative processes, which refers to processes that (...) change themselves. These processes are very common. A stretched bow is the classical Heraclitean example. However, it is easy to misunderstand what self-transformativeness is. To provide a well-formed description, I characterize self-transformative processes in terms of composition (using a non-classic mereology) and in terms of functionality (by developing the concept of self-modulating variables). Finally, I apply self-transformative processes to explain consciousness. Traces of self-transformativeness can be found in many theories of consciousness, particularly when they are stressed about their internal mechanisms. Here, I focus on Integrated Information Theory as a paradigmatic example of a mathematically well-described theory, and I demonstrate that quantitative self-transformativeness is a requirement at the very core of the integration of the information. (shrink)