The closer cortical activity is observed, the more it resembles coherent, task driven signaling between small regions.
Major features of conscious states and contents:
1. Raw scalp EEG signature of waking.
The raw scalp EEG signature of waking appears to be “irregular, low-voltage and fast” (12-70 Hz). However, direct cortical recording improves signal-to-noise by a factor of 1,000 over scalp EEG. These data show much more detailed, local, and content-specific signaling among small regions of cortex and thalamus.
Direct brain recordings in waking epileptic patients have been particularly important.
Patients wearing implanted electrode grids superimposed on cortex show prominent activation of auditory speech perception areas (Wernicke’s area) when they are asked to listen to a word attentively. When they repeat the same word, both Broca’s and Wernicke’s area are activated, precisely as one would expect.
By analogy, the audience in a football arena may give out undifferentiated crowd noises from a distance, but a set of local microphones will pick up thousands of one-to-one conversations, which are not random but highly regular, event-specific and organized.
The closer cortical activity is observed, the more it resembles coherent, task driven signaling between small regions. Newer methods, such as genetically coded voltage imaging of the mouse cortex, have very high spatiotemporal resolution and wide spatial coverage. These methods show the quiet waking state to be “near criticality,” with scale-invariant spatiotemporal patterns of neuronal activity spanning four orders of magnitude.
The near-criticality state of waking cortex implies a high level of readiness for a wide range of specific types of information processing, at multiple scales. Other typical signatures of nonlinear dynamical regimes have also been found. Walter J. Freeman and colleagues have developed analytical and physiological tools for characterizing these phenomena.
Direct brain recordings suggest a very large spatiotemporal signaling vocabulary, linking small cortical regions in a task- and stimulus-specific fashion, with oscillations from <.1 – 200 Hz. Single neurons can join or compete with these population oscillations.
Complex waveforms in the intracranial EEG are believed to reflect a phase-linked wave hierarchy from slow to fast oscillations. The traditional understanding of scalp EEG therefore appears to be an artifact of older, low-resolution, and unanalyzed recording techniques.
2. Conscious vs. unconscious vision.
Much visual cortical processing is not conscious. Retinal input is conveyed to the optic nerve via ganglion cells, which terminate in the visual thalamus (LGN) without loss of spatial resolution. LGN signals the first cortical projection area, Area V1, with point-to-point accuracy. Long-lasting binocular rivalry is enabled using continuous flash suppression, which allows for single-neuron and multi-unit recording of visual neurons throughout the hierarchy. Neurons responding to the conscious visual stream can be followed independently of those responding to the unconscious stream. For almost three decades, Logothetis and coworkers have systematically traced the two visual streams through the macaque cortex.
While the optic nerve is unidirectional, all higher-level signaling among thalamic and cortical neurons is bidirectional, giving rise to reentrant signaling or adaptive resonance, the typical signaling mode of the cortex and thalamus. From Area V1 the visual signal percolates through more than 40 topographical arrays, emerging as high-level, reportable gestalts near the top of the hierarchy. Recent findings show that reportable visual gestalts emerge in MTL (medial temporal lobe), and are propagated from there to prefrontal regions. Conscious visual contents therefore correspond well to convergent visual “gestalts” in MTL. This is an historic result, built systematically on almost 30 years of cumulative studies.
It seems likely that auditory, rhinal and somatosensory gestalts may also emerge in high level sensory cortex in those modalities. Baars et al (2013) propose that reportable Feelings of Knowing (FOKs) emerge in non-sensory regions of cortex, e.g., the dorsolateral prefrontal cortex for feelings of subjective effort. This is consistent with brain imaging evidence.
Sensory conscious contents emerge in high-level posterior cortex, while abstract Feelings of Knowing, as in feelings of mental effort or familiarity, may do the same in prefrontal cortex. This evidence is now quite strong in the case of vision, while other modalities need further testing. Consistent reports describe conscious visual cortical activity (compared to unconscious) as higher in amplitude, wider in oscillatory phaselinking, and propagated more widely, including causal (Granger) propagation (Gaillard et al, 2012). There is ongoing debate whether prefrontal activity is necessary for conscious perception. Panagiotaropoulou et al (2014), using direct cortical recording in the macaque, find that visual gestalt formation (integration) occurs in the medial temporal lobe, from where the gestalt is accurately propagated to lateral prefrontal cortex.
3. Deep sleep
Deep sleep is most natural unconscious brain state, with widespread delta waves (<2 Hz) observable in the raw EEG as regular, high-amplitude, and slow waves. Delta waves reflect coordinated pausing and firing among billions of cortical and thalamic neurons. Delta sleep serves to consolidate episodic memories acquired in recent conscious periods.
The brain behaves differently in the delta peak compared to the trough. The UP half of delta sleep allows for a rich mixture of microlevel oscillations and firing for about a second, while the DOWN half shows widespread neuronal pausing. The UP state may be a momentary waking period. The major difference between deep sleep and waking may be the regular disruption of processing during the troughs of delta waves.
Steriade (2006) has shown that slow oscillations in deep sleep reflect large, traveling waves flowing from front to back via the interhemispheric fissure. Induced unconscious states like general anesthesia are sometimes called “artificial comas,” and are thought to be different from natural slow-wave sleep.
4. REM dreams.
REM dreams resemble the waking state, with eyes closed and large, regular, and stereotyped eye movements. Scalp EEG during REM shows “irregular, low-voltage and fast activity,” suggesting waking-like spatiotemporal signaling in the C-T core. Subjects awoken during REM report rich conscious imagery and dramatic scenarios, with narrative discontinuities after perhaps 10 seconds. During lucid (self-conscious) dreaming humans can count to ten using eye movements as voluntary “start” and “end” signals, similar to the 10-30 second time of working memory.
During REM dreams sensory inflow is blocked at the level of the thalamus, so that conscious dream contents reflect endogenous cortical activity. Dream content shows “day residues” from recent waking periods, as well as motivationally driven “current concerns.” fMRI in dreams shows high metabolic activity in visual and emotional regions of cortex.
5. Brain anatomy.
Conscious contents depends on the thalamocortical complex, with major circadian states switched on and off by brainstem neuromodulation. Regions outside of the C-T complex constantly interact with, but do not directly support reportable conscious contents. Biologically, the C-T complex emerges with mammals (approx. 200 million years ago) and has anatomical homologues in the bird pallium. Pre-mammalian amnionts show paleocortex (rhinal cortex and hippocampus).
A great deal of new evidence on the connectivity pattern of the C-T system reveals small-world connectivity, which serves to optimize signal flow. The C-T system is the most highly parallel-interactive system in the mammalian brain, in marked contrast to the cerebellum, which has similar numbers of neurons but reveals parallel streams of processing. The structural road-map of the C-T system appears to be ideally suited for resolving focal uncertainties, ambiguities, and decision-points, a major biological challenge that is associated with conscious states and contents. (See Baars et al, 2013.)
Like the structural map of the C-T system, the power in EEG frequency bands follow an inverse frequency law ((1/f) EXP B).
6. Sensory gestalt “broadcasting.”
Neuronal activity corresponding to conscious gestalts propagates widely in the brain, as indicated by highly distributed long-term memory traces, implicit learning, and biofeedback training of autonomic and motor functions. The very fact of accurate reportability implies that executive regions like the prefrontal cortex receive accurate source information from posterior sensory regions.
7. A very wide range of conscious contents.
The conscious state has an extraordinary range of contents — sensory perception in the various senses, endogenous imagery, emotional feelings, inner speech, abstract concepts, action-related ideas and Feelings of Knowing such as familiarity, confidence judgments, feelings of effort, and much more. The set of conscious contents may be open-ended. Spontaneous conscious mentation is believed to reflect “current goaldriven concerns.”
8. Informativeness. (See automaticity)
Conscious contents fade when input signals become redundant, a general phenomenon that can be observed across the senses. Sensorimotor skills also fade from conscious access with repetition. Such redundancy effects apply to high-level semantics as well, as in the case of semantic satiation.
A classical example in vision involves stabilized retinal images. During normal vision the eyes exhibit a constant, fast tremor, so that incoming light edges and gradients do not fall on the same retinal receptors. If a tiny light projector is mounted on a contact lens so as to stabilize light input to the fovea, the image will rapidly fade from consciousness. Any change in the incident pattern will return the stimulus to consciousness.
These very general effects suggest that sensory consciousness thrives on informative input, rather than physical energy patterns as such. The senses are not simple energy transducers, but fast-adapting neuronal networks at multiple levels of input analysis. When a constant stimulus becomes predictable it is no longer consciously perceived.
Thus “informativeness” seems to be a necessary condition for conscious perception.
9. The fleeting nature of conscious events.
Our experience of the sensory present may last a few seconds, while our cognitive present may be less than half a minute. In contrast, much unconscious knowledge resides in long-term memory, interacting constantly with sensory and endogenous input.
10. Internal consistency.
Conscious contents are marked by a strong consistency constraint. For example, while multiple meanings of most words are active for a brief time after presentation, only one becomes conscious at any given time. This point also applies to perceptual stimulation (as in perceptual ambiguities or competing inputs), and it may also apply to beliefs, as in the case of cognitive dissonance.
In general, of two mutually inconsistent contents, only one can become conscious at a time.
11. Limited capacity and seriality.
Many careful experiments show that momentary conscious capacity is only 1-4 separate “items.” When unpredictable items are presented visually while the subject repeats a short word like “the… the… the” this radically limited capacity appears consistently.
Thus the isolated capacity of conscious contents at any given moment is radically limited. We can circumvent these narrow limits by chunking, stimulus organization, and learned associations to established knowledge and skills in long-term memory. Yet the flow of isolated conscious items is serial, in contrast with the massive parallelism of the (mostly unconscious) brain when it is observed directly.
12. Multiple levels of binding (integration).
Sensory cortex is regionally specialized such that different cortical “visuotopical maps” respond to different visual features such as retinal location, size, contrast, color, object identity and motion. One classical question is how these cortical arrays coordinate their activities to generate the integrated gestalts of everyday perception.
Recent evidence implicates MTL (medial temporal lobe) in gestalt integration.
13. Multiple problem-solving functions.
Because conscious cognition is involved in perception, learning and novelty-processing it appears to be necessary for (novel) problem-solving. Herbert Simon and Alan Newell’s studies of explicit problem-solving protocols beginning in the 1950s, demonstrated the radical limited capacity of conscious cognition, and led to their later work on cognitive architectures, which have both a small-capacity and large-capacity component.
In explicit problem-solving, as in mathematical proofs, every needed step is conscious. But most real-life problems have predictable and automatic components — such as the act of reading this sentence. Most real-life problem solving involves alternating conscious and unconscious moments.
Based on thought monitoring studies it has been argued that the spontaneous flow of thoughts involve multiple “threads” of conscious and unconscious elements, intertwined with each other. Jerome Singer and colleagues have shown that spontaneous thought is mostly driven by “current concerns.” In healthy subjects the stream of spontaneous cognition is neither random nor dysfunctional. It appears to be goal-directed, often unconsciously.
Conditions like depression show repetitive ruminations on unrealistically self-critical thoughts. Cognitive behavioral therapy studies strongly suggest the existence of half-conscious or unconscious dysfunctional beliefs that drive negative moods. Thought monitoring studies in traumatized subjects often show unwanted and intrusive thoughts, feelings, images, and intense emotions.
These findings helped to establish post-traumatic stress disorder (PTSD) as a formal psychiatric category.
14. Implicit self-attribution — the observing I.
Conscious experiences are generally attributed to an experiencing but implicit self, the “observing self,” as William James called it. Self-functions appear to be associated with precuneus and orbitofrontal cortex in humans. However, it engages a wider network of cortical and subcortical regions, such as the vestibular balance system.
There is little evidence that the “observing ego” can report its own functioning, since it is implicit. Self-knowledge is a cognitive skill that varies radically between individuals.
Informal beliefs about the implicit ego are generally inaccurate. Rather, the perceiving “I” seems to involve an implicit framework within which conscious events are defined, but which is not conscious in and of itself. For example, the egocentric visual maps of the parietal cortex work in coordination with allocentric (objectcentered) maps, and with motor cortex, much like gravitational lines of force around large masses in physics. Both hippocampal/entorhinal and parietal regions are thought to have egocentric and allocentric maps.
15. Accurate reportability.
Conscious contents are reportable by a wide range of voluntary responses, often with very high accuracy. The conventional operational index of consciousness is based on accurate reportability.
Notice that humans are also distinguished by a lush imaginative life, as shown by way of legends, other-worldly beliefs, dreams and waking fantasies. Thus our brains have dual specializations — we can be extremely accurate (which is essential in dealing with dangers and opportunities) and we are also very much driven by imagined events.
16. Subjectivity.
Consciousness is marked by a private flow of events available only to the reporting observer. Reportability applies to the classical senses, but not to the vestibular (balance) sense, for example, nor to parietal control of sensorimotor reaching, syntactic analysis, and much more. The brain bases of these unconscious functions is not wellunderstood.
17. Focal-FOK distinction.
While conscious contents tend to be viewed in terms of focal percept-like contents, Feelings of Knowing (FOKs) are common and important. Judgments, intuitions, abstract concepts, and vivid expectations are experienced as FOKs, including the famous tip-of-the-tongue state, which involves complex semantic and linguistic knowledge.
This may reflect the distinction between percepts and concepts.
18. “Consciously-mediated” learning is very effective.
The evidence is strong that non-trivial learning requires some time for conscious access. Many thousands of subliminal perception experiments have tried to show nontrivial unconscious learning, but robust learning of novel material has not been found.
New claims for unconscious learning appear often, but seem to be limited to priming of pre-existing knowledge. Stored knowledge can be easily activated. For example, unconscious pictures of snakes may trigger amygdala activation, though there is still debate on this point.
However, “consciously mediated learning” is very effective. In a classical experiment by Standing (1977), subjects were shown thousands of conscious pictures for less than 10 seconds each. They were not asked to memorize them, but only to pay attention.
Several days later they were able to tell “old” from “new” pictures at more than 90 percent accuracy. Thus robust learning occurs merely when information becomes conscious. Such high learning efficiency has never been reported for subliminal perception.
These “easy-learning” results may seem counterintuitive, because we are used to academic study, which is effortful and demanding. The difference is in the task conditions. Academic learning requires deliberate memorizing and recall on demand, while highly efficient incidental learning is found for easier retrieval tasks, such as old vs. new recognition and cued recall.
The term “implicit learning” is often misunderstood to mean “unconscious learning,” but this is not correct. Implicit learning experiments always show a set of conscious stimuli to the subjects. What is genuinely unconscious about “implicit learning” is the process of inference that occurs, once the conscious stimulus set is perceived and learned. Implicit learning is vital for the acquisition of natural language, but there, too, infants hear numerous conscious utterances before they implicitly infer the regularities of their native language. Adults naturally engage in “baby talk” with infants, imitating infant tonal melodies while using adult words. Language acquisition therefore seems to be consciously mediated.
In sum, the weight of evidence shows that significant learning requires conscious mediation. Compared to the weak effects of unconscious learning, consciously mediated learning is both effortless and effective.
19. Experienced stability of contents.
Conscious percepts are impressively stable, given the very high variability of proximal physical stimuli that are nevertheless perceived as constant. Even abstract cognitions, such as beliefs, concepts, and personality patterns, are extremely stable over the adult lifetime.
20. Allocentricity (Object-centeredness).
Conscious percepts generally have allocentric character (object-centered), though they are also shaped by unconscious egocentric maps of the parietal cortex. After one-sided parietal damage to the visual dorsal stream, the opposite side of the visual field disappears from consciousness. Such “visual neglect” shows that parietal maps do not support conscious vision by themselves, though they are needed for ventral feature maps to become conscious. They are said to be “contextual.”
21. Consciously-mediated decision making.
Conscious mediation is useful for making decisions, for goal pursuit and problem-solving. These tasks require conscious moments, intertwined with unconscious periods for routine and predictable processes.
Similarly, voluntary decision-making involves both conscious and unconscious moments. Essentially all cognitive tasks are mixtures, since each kind of process has its own pros and cons.
Consciousness In Philosophy and Science
A clear boundary between philosophy and science is recent, starting about 1900. Historically, philosophers made important empirical as well as conceptual contributions. Descartes studied the optics of oxen eyes and the bilateral organization of the brain. William James summarized an immense body of experimental facts in his Principles of Psychology of 1890. The Asian tradition of experiential observations and mental praxes may date back to the Indus Valley culture of some 4,000 years ago.
However, with the rise of positivism around 1900, philosophers focused on analyzing words and arguments, and avoided empirical topics. Philosophers of mind tend to study the mind-brain question, with its three traditional perspectives of physicalism, mentalism and dualism. Common sense alternates readily between public “physical” observations (e.g., the sight of an aspirin) and “mental” ones (e.g., noticing that an aspirin cured a subjective headache).
The sight of a physical aspirin can be directly shared with others, but a fading headache cannot.
Modern philosophers tend to discuss consciousness from a subjective perspective. The major question therefore becomes “what is it like to be a certain conscious being?”
For scientists, Karl Popper’s distinction between empirically falsifiable and non-falsifiable claims continues to be fundamental. Empirical falsifiability is necessary for science.
[Excerpted from Part I – Major Features of Conscious States and Contents & Consciousness in Philosophy and Science from Bernie Baars’ latest book “On Consciousness: Science & Subjectivity.”]
Global Workspace Theory (GWT) began with this question: “How does a serial, integrated and very limited stream of consciousness emerge from a nervous system that is mostly unconscious, distributed, parallel and of enormous capacity?”
GWT is a widely used framework for the role of conscious and unconscious experiences in the functioning of the brain, as Baars first suggested in 1983.
A set of explicit assumptions that can be tested, as many of them have been. These updated works by Bernie Baars, the recipient of the 2019 Hermann von Helmholtz Life Contribution Award by International Neural Network Society form a coherent effort to organize a large and growing body of scientific evidence about conscious brains.
