Components of


Psychology of Subjective Experience


Theory of consciousness :

'Is reduction of consciousness feasible?'


- Characteristics of consciousness

[First website version 16-02-2009;
revised version 07-03-2020]

Characteristics of consciousness

Below we will briefly discuss a number of aspects and phenomena that qualify as candidates for features of consciousness.
The candidate characteristics of consciousness can first be classified into the following main categories:

With these characteristics we can illuminate all kinds of aspects of consciousness, and try to form a fairly clear overview of those aspects and properties that consciousness comprises as a phenomenon. The latter provides a first basis for understanding and explaining it.

(I) Non-unique characteristics of consciousness.

(I.1) Non-unique characteristics - that are neuronal related.

First we have non-unique characteristics of consciousness that are derived from physical phenomena. These mainly concern properties of brain processes, or neurophysical characteristics: certain features, phenomena and processes in the nervous system that (almost) always occur simultaneously with conscious experience.
{Nb There are all sorts of measuring instruments that provide indications and data with which certain characteristics of the activity of the nervous system can be detected in a fairly reliable manner.

Physiological measures or indicators for those characteristics are, for example:

Central nervous system:

EEG: Electro Encephalo-Gram.
ERP: Event Related Potential.

Somatic system:

EMG: Electro Myo-Gram.
EOG: Electro Oculo-Gram.

Autonomous nervous system:

HR: Heart Rate.
BP: Blood pressure.
GSR: Galvanic Skin Response.
Pupil dilettation.

Endocrine system:

Adrenaline levels.
Nor-adrenaline levels.

Measurements for performance, task execution are for example:

Measurements for 'Steady State' or 'Probe' functioning.

Indicators for characterizing:
Memory Performance.
Selectivity of attention, etc.

Measures for subjective experience.

'Traite' or 'State' measures.

Quality of the subjective experience:
Kind of emotion.
Required effort.
With all these and other measures and indicators, it remains obvious that they only reflect information about characteristics that are immediately empirically observable. We simply keep seeing, hearing and touching only the 'outside'. For our physical senses there is no sign whatsover of the 'mental inner' or 'inner life' of one another. }

A large number of statistical correlations have been found from neurophysiological and biopsychological research of reported contents of consciousness with physical locations, substances and processes in the nervous system: the so-called 'neuronal correlates'.
(neuronal correlates of consciousness, NCC: cf.e.g. Kandel & Schwartz, 1985).
It is therefore clear that consciousness is usually accompanied by a certain degree, level or mode of activity of the (central) nervous system. This activity usually occurs in the daily waking state, but also in the more 'active' stages of sleep, in particular the so-called REM sleep, the sleeping stage in which also most episodes of conscious dreaming occur.

(I.1.1) Characteristics of neuronal aspects - related to consciousness.

States of consciousness are generally associated with specific modes or activities of all kinds of neuronal components, from overall to local scale, and from macro to microscopic scale.
We will briefly describe a number of known characteristics of these types of activity below:

Global internal states of the organism.

The most important of these are:
(1) Waking state (W), which mainly includes active functioning (arousal, active waking, AW) and vigilance (alertness);
(2) Conscious dreaming, which mainly takes place during the so-called REM sleep, also called active sleep or paradoxical sleep (PS);
(3) Special states such as - not too deep - hypnotic trance (without complete elimination of conscious sensations).


Activity of special functional systems of the nervous system.

This is in particular the system for active functioning, the orthosympathic (the so-called effort system, Sympathetic-Nerve Activity, SNA), and more specifically and centrally the control system for vigilance, the Ascending Reticular Activating System (ARAS) in the formatio reticularis, a net-like system of nuclei and circuits in the brainstem (truncus cerebri). This activity is accompanied by, among other things, faster heart rate (heart rhythm), higher levels and greater variance of blood pressure, higher tone of skeletal muscles, and so on.


Activity of certain neuro-anatomic areas.

Consciousness seems to be located in specific neuronal areas. Traditionally, a very simple reasoning is followed to identify the brain areas which might be locations of consciousness.
• People can communicate with other people, especially verbally (talking, writing), in a way that usually works better than with (other) animals. (Of course, for many animal species the same will apply with respect to humans).
• This communication shows that people report conscious subjective experience, which is often recognizable or even tactile to others of the same kind - at least much easier than from the observable signs of animals. (The latter of course says nothing about the comprehensibility of communication that animals may experience among themselves).
• It is on this basis that consensus arose among humans that humans are conscious, and animals are not or practically not. In this reasoning the stacking of fallacies is obvious.
• Further, there are certain demonstrable differences with animals, like a more complex intelligence on certain cognitive tasks, and more highly developed brain areas that make this possible. These areas are mainly located in the upper cortex cerebri. On this basis it was concluded: subjective consciousness is pre-eminently linked to such brain areas that are more developed in humans. However, by systematically focusing unilaterally on functions that are more developed in humans as opposed to animals, one may of course easily fall prey to 'selective inference' (selection bias) and ignore capabilities of animals.
• Next, by strong simplification it is assumed that a global 'division of labour' or specialisation applies: The unconscious processes appear to be more associated with brain areas that are relatively 'older' and 'more animalistic': they lie in lower areas (subcortical, infernal), at the back side (dorsal), and at the right (dextral) of the brain: mainly the cortex cerebri, and to a lesser extent, the allocortex with the limbic system.
While the conscious processes generally are more likely present in areas that are relatively 'newer' and 'more humane': they lie in higher areas (cortical, supernal), at the front side (frontal) and at the left side (sinister) of the brain:
mainly in the mediate brain (diencephalon, midbrain (mesencephalon, brain stem (truncus cerebri), and extended marrow (modulla oblongata).

This representation of affairs is, however, unsustainable with regard to the neuronal areas that may cause or maintain consciousness as a mode of functioning of the brain. Crucial to the emergence and the maintenance of conscious functioning remarkably appear not to be, as the myth would have it, the 'higher' brain areas, like cortex cerebri, that we associate with primates and humans, but most notably the evolutionary 'older' fish, amphibians and reptile brain.

A number of neuronal phenomena which usually co´ncide with ordinary waking consciousness, appear to gradually increase shortly before the waking state, and only decrease again after loss of consciousness - in deep sleep, anaesthesia and so forth. In particular, these concern factors causing increased vigilance and global activation (arousal ) of the organism. With higher vigilance typically an increase takes place of the intensity of consciousness, as well as increase of alertness, extroversion, effort and action readiness, and motor mobility (dominance of the sympathetic system).
The overall level of vigilance thus forms an important neuronal correlate of consciousness. It is mainly arranged by the so-called Ascendent Reticular System, located in the central nervous system, in particular in a network-like structure of fibres and nodes called formatio reticularis. The formatio reticularis extends over the brain stem (truncus cerebri) - consisting of exstended marrow (medulla oblongata) and bridge ( pontis varolis) - the midbrain (mecencephalum) and the mediate brain (diencephalum, especially the thalamus).
{Nb. The formatio reticularis is already to be found, albeit in a rather rudimentary form, in invertebrates, inter alia round beaks (Cyclostomae) or also jawless marine fish (Agnatha) such as hagfish, pricks and stings (lampreys). In more fully-fledged form it's already there in primitive vertebrates, including the cartilaginous fish (Chondrichthyes, Elasmobranchii) such as cuttlefish, dragonfish, rays and sharks; the bonefish (Osteichthyes), consisting of the ray fins (Actinopterygii) like sturgeons, and the real bony fish (Teleostei) to which approximately 95 percent of all fish belong, and finally the brush fins or muscle fins (Sarcopterygii), like lungfish, that are most akin to four-legged animal species. }

An increasing arousal follows increasing activity of specific nerve nuclei in the brainstem (in the formatio reticularis) and the release of specific neurotransmitters (especially mono-amino acids and glutamate).
The waking state is related to activity of among others the following neuro-anatomical structures, that all produce neuro-transmitters that have a fast, activating effect (an excitatory nature).
  • The locus coeruleus (LC) in the midbrain (tegmentum mecencephali):
    it produces Noradrenaline (NA).
  • The substantia nigra (SN) in the midbrain (tegmentum mecencephali): these produce Dopamine (DA).
  • The nuclei reticulari pontinis medialis (FRPM) in the bridge (the area peribrachium): these produce Acetylcholine (ACh).
  • The nuclei raphei (NR) in the inner marrow (medulla oblongata, centralis): it produces Serotonin (5-HT).
All these structures and substances play a role in regulating vigilance, arousal and sleep-wake rhythm, and thus also with the emergence and maintenance of consciousness. Moreover they play a role during REM sleep and its episodes of mental activity and conscious dreaming.


Activity of specific neurotransmitters.

The aforementioned neurotransmitters play a rol as follows:
  • NA and DA are mono-amino acids, in particular catecholamines, that play an important role in waking state and arousal.
  • Ach is a typical neurotransmitter for REM-sleep.
  • 5-HT is associated with relaxation, feelings of comfort and a sound sleep.
  • Glutamate is one of the most abundant amino acids in the human body, also present in almost every part of the nervous system. This is the fastest and most powerful excitatory neurotransmitter, playing a role in well over 90 percent of the synaptic connections in the human brain. It furthers synaptic plasticity and is thus involved in processes of adaptation, accomodation, learning and memory in the entire nervous system. Glutamate itself serves as metabolic precursor for the neurotransmitter gamma-Aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the nervous system.


Activity of specific neuronal cell types.

In effect of the aforementioned subcortical processes and substances, functions in the more 'modern' areas of the cerebral cortex (cortex cerebri) are among others globally stimulated, activated and modulated.
{Nb Conscious exercise of will seems to involve a specific neuronal circuit in which 'higher' brain organs do play a role, it runs between cortex, basal ganglia and thalamus, the so-called 'cortico-basal ganglia-thalamo-cortical loop' (cf.Newman, 1997).
After preliminary unconscious processing by "interneurons", principal neurons present in the cortex provide for decisions about sending of 'summarized' signals that may come under conscious attention (P.M. Churchland, 1993).
Those principal neurons particularly constitute of so-called pyramidal cells: relatively large, fast-acting neurons that fire their signals in powerful bursts (bursty pattern) with frequency upto 5 Hz. They work activating (excitatory) instead of inhibitory.
These pyramidal neurons mostly lay in the neocortext (and further in the hippocampus and the amygdala ), in particular in the deeper, so-called inner pyramidal layer (cortical layer V, the lamina ganglionary; cf. Crick, 1994, p.251). They seem to be mainly involved in higher sensory, motor and cognitive processing, memory tasks, and conscious intentional attention (Shepherd 1994, Crick 1994, p.251, Ransford 1995).


Post-synaptic (dendronal) receptors.

Important in this regard are post-synaptic receptors of the relatively quick, NMDA-activated type (NMDA = N-methyl D-asperate). These are found in the dendronal synapses of pyramid cells.
They are partially voltage-sensitive, and have a critical voltage threshold of -35 mV of the postsynaptic membrane potential to become activated by presynaptic release of fast neurotransmitters such as glutamate (H. Flohr, U. Glade, D. Motzko, 2000; in: J. Schulte am Esch, J. Scholz, P.H. Tonner (Eds.)).
In partical the NMDA receptors become disabled with general anaesthesia. Thus they turn out to be crucial for maintenance of subjective consciousness.


A dominant role of specific ions.

In the transition from unconscious to conscious processing specific ions may play a role. These are mainly Calcium, but probably also Sodium and Potassium. They are important in processes such as:
• Interneuronal signal transmission,
• Transduction of membrane potentials to internal chemical signals,
• intracellular signal conduction.
Especially ionized Calcium (Ca++) serves, among others in NMDA receptors, for transduction of an electric signal and its transposition into a chemical signal inside the cell, which can help to depolarization of the cell. (Cooper et al. 1991, Levitan & Kaczmarek 1997, p.124).


Specific Brain activity.

During conscious episodes, the active brain areas show, roughly said, specific signal patterns and brainwaves with typical characteristics. This is particularly the case during wakefulness but also, albeit much less unambiguous, at various sleep stages with dreamlike mental activity (mentation) that is subjectively noticeable as conscious sensations.
The general - and obvious - idea is that there is a symmetry between processes on distinct levels of functioning:
• while the global activation of the central nervous system increases, in particular of the "higher" and "newer" cortical brain areas;
• the subject's mental activity will increase proportionally;
• and thus the presence, intensity and variation of consciousness will also increase.
First of all it turns out that during conscious episodes a global 'undertone' of activation occurs, as well as local activity in connection with specific stimulation, focused attention, and intensive mental processing or effort.


Brain activity during conscious waking state.

During conscious episodes the action potentials of neurons of the neocortex show an active and brisk discharge behaviour. The discharge rhythm has, as represented by a electroencephalogram (EEG), a relatively high firing speed (frequency of action potentials); this lies in case of active and intensive functioning in the ranges called Beta (approx. 15-35 Hz) and gamma (approx. 35-85 Hz) with low signal power (approx. 2-20 ÁV); and in a calm and relaxed state within alpha range (approx. 7-15 Hz), with higher amplitude (approx. 20-50 ÁV).
In active waking state neurons react highly independent of each other on their specific input signals. As a result the cortical EEG shows an irregular, so-called dissynchronized lapse. Because of this it seems like the neocortex shows overall a seemingly chaotic or random discharge behavior.
In a more relaxed state the brain activity shows a more diffuse and monotonous conduct, and the EEG shows a more regular, synchronized routine.


Global stimulation during waiting episodes.

In conscious episodes the activity of the cortex is globally modulated through continuous stimulation from neurons in subcorticalareas: in particular the brainstem (especially the serotonergic nuclei raphae) and the midbrain (especially the noradrenerge nuclei locus coeruleus). During waking state (W) this concerns PS-off cells, and during REM sleep PS-on cells. The characteristic signals from these cells are tonically : yhey have a prolonged elevated baseline activity, and as a result they exhibit a box-shaped signal pattern. They may provide a higher signal-to-noise ratio of brainwaves in thalamus and cortex.
As a result more prominent and thus deterministic signal patterns may become possible. It is thought that hereby 'higher' mental functions are supported, in particular sharpening of attention and relatively complex information processing (Sutton, et al. 1992; Keeler, et al., 1989; Servan-Schreiber, et al. 1990; Siegel, Nienhuis & Tomaszewski, 1984).


Selective activation in conscious episodes.

Specific stimulation of cortex areas causes signal transmission to take place with fast, excitatory synaptic transmission. Whith sensory stimuli that are more salient - i.e. strong, deviant or variable - as in task exercise, the EEC shows typical event-related discharges (event-related potentials, ERPs) (cf. Flohr, 1992). The signal in doing so has a high amplitude, and a frequency of about 40 Hz., which falls within the high-frequency range of 35-85 Hz., which is typical for so-called gamma waves (cf.Crick & Koch, 1990; also 1995; 1998). It is found in various sensory modalities - mainly related to observation of environment and sense of movement (exteroception and proprioception).


Brain activity during conscious dreaming (especially during REM sleep).

Not only during everyday watchfulness, but also while sleeping, there are conscious sensations, which occur in the form of dreams.
The wake-sleep rhythm, the circadian rhythm, is centrally controlled by an area in the hypothalamus: the nucleus suprachiasmatic (or supraoptic), (NSC).
• The internal 'clock' of this nucleus is set on basis of changes in the light from the outside. The NSC receives this information from the light-sensitive ganglion cells in the retina through the optical trajectory ( tractus opticus, tractus retinohypothalamicus, RHT).
• The NSC transmits its circadian signals amongst others to the nucleus paraventricularis (PVN) in the hypothalamus. From the PVN a signal is sent to the preganglionic neurons through-out the spinal cord, belonging to the autonomous, sympathic nerve system.
• The latter sents out a signal to the peripheral ganglion cervical superioris (SCG) at the front of the second and third cervical vertebrae.
• Next, via noradrenergic (NA) fibres these signals reach the pineal gland, glandula pinealis or epiphysis (EF), located in the mediate brain (diencephalon) under the brain bar (corpus callosum). In response to signals from the NSC about diminishing ambient light the epiphysis provides the conversion of serotonin into melatonin, a monoamine neurohormone. (As also happens in the nucleus raphae). Melatonin is an important factor in the induction of sleep.
• Finally the epiphysis secretes more melatonin into the bloodstream.
• A number of fibers of the photosensitive retinal ganglion cells reach the lateral and ventrolateral preoptic regions, that control the production and secretion of hormones by the hypophysis, located at the bottom of the hypothalamus. These hormones affect various circadian bodily functions (Hattar et al., 2006).
Towards the end of the waking state, the supply of norepinephrine/ noradrenaline (NA) to the pituitary gland, and with it the secretion of melatonin by the epiphysis.

Characteristics of sleep stages:

The nature and intensity of moments of conscious dreaming appear to vary with the course of sleep. It has been shown that sleep usually takes place in cycles of approx. 60 to 90 minutes (a BRAC = basic rest to activity cycle), each with a fixed number of typical phases or stages. Some typical phenomena at various stages of sleep are these:
The first three stages of sleep are the non-REM (NREM) stages (N1 to N3):
  • At stage N1, the 'beginning sleep' (sleep onset, SO) there is a transition from relaxed waking state with alpha waves (approx. 7-13 Hz) to "drowsing" or "dozing off" with theta waves (approx. 4-7 Hz).
  • At stage N2, of light sleep without consciousness, a further slowing down of brainwaves takes place.
  • At stage N3, the 'deep sleep' (slow wave sleep, SWS, formerly called stages 3 and 4) the brainwaves have high signal power (75 ÁV), but they slow down to delta waves (approx. 0.5-4 Hz).
The final sleep stage is that of the so called REM sleep. Here the brainwaves shows features closely resembling those in waking state: high frequencies, especially in the beta range (approx. 15-35 Hz), low voltages (approx. 10-20 ÁV) and asynchronous lapse. in the secondary cerebral cortex, more specifically visual areas in the occipital-parietal areas and auditory areas in the forebrain.

Consciousness during sleep.

It turns out that dream processes are primarily taking place in the final phase of the sleep-wake cycle. This sleep state has a whole range of characteristics that set her apart from those in the other four sleep phases, and is often referred to as the "active," the "paradoxical", the "de-synchronized," or the "REM" sleep. The latter because of the performance of typical Rapid Eye Movements. (For the first reports of this connection cf. Aserinsky & Kleitman, 1953; Dement 1955; Dement & Kleitman 1957; Arkinet al., 1978).
For REM sleep, dream recall is rather high: approx. 82 percent on average (T.A. Nielsen, 2000, 'Mentation in REM and NREM sleep'). In REM sleep dreams appear a little longer as well, having a relatively vivid and 'anecdotal' form. Based on these findings, the conviction found general acceptance that REM sleep is an inherent feature of dream activity, in particular conscious dreaming (cf.for an overview: Nielsen & Montplaisir 1994; Lavie 1994; Rechtschaffen 1994; Berger 1994; Foulkes 1993).
Furthermore, the beginning of the REM sleep phase is fairly easy to recognize on the basis of specific neuronal correlates or markers. Some of these constitute physiological indicators of mental activity in a waking state - which is usually accompanied by consciousness. It is therefore possible that these correlates may also, at least partly, apply to moments of conscious dreaming.

Further interesting are characteristic waves of approx. 2 mV, thate arise in the pons and follow a pontar-(thalamo-)genicular-occipital route: and are therefore called PGO waves. These signals are typically phasic: they have a short, high signal, which is peak-shaped (burst mode firing).
  • The PGO waves start from - especially cholinergic - "PGO-on" cells, located in the region peribrachium in the pons (especially the nuclei tegmentis meso-pontinis, lateralis dorsalis) and in the midbrain (especially the nuclei tegmenti pedunculo-pontinis, lateralis medialis).
  • The efferent fibres (axons) of these nuclei project to the forebrain (procencephalon), more specifically the thalamus (in particular nucleus genicilatum lateralis).
  • The PGO signals further reach the endbrain (telencephalon), in particular the visual cortex (lobus occipitalis ).
The PGO signals seem to cause, among other things a selective stimulation of secondary visual and auditory areas in the forebrain. It is conceivable that they can thus contribute to the typical, 'cinematic' dream images that people often experience during REM sleep.
It is thought that through this specific REM activity in the brain a kind of "pseudo-waiting state" is being created, in which learning experiences can be consolidated, as it were in vitro. However, for the time being this is highly speculative.
During REM sleep there are also in the hippocampus autonomous, short-living, tonic synchronized discharges, in waves of slower theta rhythms (4-7 Hz).

Conscious dreaming and REM sleep.

Clearly there appears to be a certain relation between REM sleep and conscious dreaming. However, these are only weakly correlated.

REM sleep is not sufficient for conscious dreaming.

There is still about 18 percent of REM sleep with no memory of a dream. REM sleep therefore does not seem to be a sufficient condition for remembrance of dreams.

REM sleep is not necessary for conscious dreaming.

People also report dream-like mental processes (indicated with the broad term mentation) when they wake up from other than REM sleep stages, the so-called NREM sleep (Goodenough et al., 1959; Foulkes 1962; 1966; 1985; Foulkes & Vogel 1965; Foulkes et al. 1966; Vogel et al. 1966; Pivik and Foulkes, 1968; Vogel 1978; Foulkes 1982; Foulkes and Schmidt, 1983; Antrobus, 1983; Rechtschaffen et al., 1963a; Fein et al. 1985; Cavallero and Foulkes, 1990; Cavallero et al., 1992; Stickgold et al., 2001). For the different NREM stages, the average scores of dream memory roughly amount: in stage 1 ( sleep onset, SO) approx. 31-76 percent, in stage 2 approx. 40 percent, and in stage 3 and 4 ('deep sleep', slow wave sleep, SWS) approx. 40-60 percent. The average score of dream recall from NREM sleep is less than half of REM's, but it's still significant: i.e. on average 43 percent (T.A. Nielsen, 2000).
It's to be expected though that the neurophysiological characteristics of NREM sleep with the most vivid mental activity will resemble having the characteristics of REM sleep, with typically associated mental activity (Nielsen, et al. 1995). Conversely can be expected that low cortical activity during sleep with maximal brainwaves synchronization cannot be associated with any mental activity of significance.
However, on the other hand people report that, even after waking up from the deepest sleep stages, when overall cerebral activity has been reduced to a minimum and the brainwaves only show a slow, unified and synchronous rhythm - and therefore offer a negative indication for neuronal activity - they had certain mental activity in the form of dreams that they seem to have experienced consciously. (P.C. Cicogna, V. Natale, M. Occhionero, M. Bosinelli, 2000). ".. vivid imagery may appear well before classical signs of REM sleep, during a period of apparent EEG-synchronized sleep" (Steriade et al., 1989, p. 2228; cf.also McCarley, 1994).
In all these cases, it remains difficult to determine whether there really are conscious dreams to be remembered, or just unconscious mental processes reported, that are only 'remembered' afterwards, during or after waking up.
All in all, we can't say that REM sleep definitely is a prerequisite for remembrance of dreams.
In short, the specifics of REM sleep during conscious sensations may give clues on the neurophysical factors which are quite closely related to the causal conditions for consciousness - but the last ones are thus far not revealed.


Other potentially relevant neurophysiological phenomena.

All kinds of other neurological processes and functions are proposed to be characteristics, carriers or causers of consciousness, e.g. special micro-biological structures such as so-called ' microtubules', which are proteins who are located in certain neuro-synaptic gates and channel (cf. a.o. Stuart R. Hameroff & Roger Penrose, 1996).
It should be noted that all these theories are highly speculative, or even improbable in more ways than one (cf.a.o. R. Grush & P. Smith-Churchland ).

This very concise overview already shows that there are many neuro-physical properties related to consciousness.
The neuronal activity which is usually accompanied by consciousness consists of a combination of innumerable factors and variables which interact in countless ways that are highly complex and still largely unexplained. It is therefore very difficult and often not (yet) possible to isolate, distill and determine causal factors for consciousness out of the entire system of neurophysical activity.
The crucial question still is whether there are any neurophysiological symptoms which constitute uniform characteristics that can be used to demarcate consciousness. Put in another way: can be shown that these characteristics are never present without consciousness present, and vice versa? For that purpose at least two things must be demonstrated:
(1) The characteristics must be truly only present, and play an active role, in relation to the actual presence of subjective consciousness.
(2) It must also be proven that these characteristics cannot apply as well, to a greater or lesser extent, to unconscious, preconscious or unconscious phenomena.
Results of neurophysiological examinations do indicate, for some of these characteristics, to certain tendencies in that direction. But there's still no definite answer (cf. among others C.V. Borst, 1970).

Some contra-indications

There are also indications that undermine conclusive correlation between cortical activity and presence of consciousness:

Not necessarily unique.

It's difficult to determine to what extent all characteristics of cortical activity really are unique for consciousness, that is, never are present without consciousness.
A lot of those factors, variables and interactions turn out to be, and sometimes to a large extent, active during unconscious states. In that case it is excluded that they really are a sufficient indication for consciousness.

Not necessarily inherent.

In addition, it is difficult to determine whether features like high cortical activity really are inherent to conscious, that is, are always present when consciousness is present.
This showes that it is also impossible to designate specific neuronal characteristics which are strictly necessary for subjective consciousness in contrast with function unconsciously.

Possible inverse causality?

Thus a tricky point is that certain cortical activity can be strongly related statistically to consciousness, while there still may occur exceptions or contraindications that are not due to chance variance (noise or random error), but to a systematic structure of the interaction between body and 'mind': where neurophysical factors in turn are effected by conscious mental processes. After all, certain conscious mental maneuvers or operations (like thinking, fantasizing, deciding, etc.) demonstrably turn out to have an effect on the processes in the brain: they are followed by proportionate changes in those processes, and although this yet again can only be proven to be a chronological relationship, it cannot strictly be excluded that this in addition could be a causal relationship.
We'll look into this in more detail in reviewing forms of neurophysical reduction of consciousness.

(I.1.2) Inherent characteristics of consciousness that are physically- and information-related


('Pseudo-physical' characteristics of consciousness).

There are further features that seem to be inherent to consciousness, and at the same time indirectly associated to neuronal phenomena. Moreover, they have to do with ordering relations and form aspects of conscious experiential content. In that respect we can consider them as information-related characteristics.
But apart from that, they are related in indirect manner, and at least at face value, to various neurophysical or at least physical processes and properties. Thus these characteristics seem to constitute combinations of physical factors and information aspects. They are in other words features that are not, or not necessarily, unique to consciousness.
In some ways they look like physical properties but they're not actually to be determined as 'purely' physical.
Examples are:

Degrees in consciousness and experience intensity.

The intensity of consciousness and experience is considerably correlated at the global level of neuronal activity. (We can find an analogy for this in physical measures of intensity, such as power, energy, and the like).


Degrees in conscious-to-unconscious transit phases.

Conscious states, episodes or phases have a gradual transition, boundary or demarcation in time as opposed to unconscious or less conscious phases, processes and contents. This is strongly related to the sleep-wake rhythm, and within the sleep cycle, with the most striking phase changes: (1) from waking to the first stages of sleep or non-REM stages, (2) from the last to the REM sleep stage with any conscious dreams, (3) and from there to (conscious) awakening. It appears somewhat harder to determine of psychological contents where precisely the boundary lies between conscious experience and unconscious processes, because this is highly individualized and instantaneous (the Introspection problem).
With respect to sleeping and waking stages we can find numerous characteristics and correlates in processes and structures of the nervous system. But to decide which one of these possibly delivers a robust causal contribution to consciousness, appears to be an extraordinarily complex problem.


Degrees in conscious-to-unconscious contents.

There is a gradual delimitation of conscious content as opposed to unconscious or less conscious content. The selection of mental contents for consciousness is somewhat indicated by the direction of conscious attention, and the activation of specific neuronal areas such as sensory and somato-sensitive function fields in the spinal cord, the extended marrow, the thalamus, and the cortex.


Indirect relation between modalitiesof subjective mental content and physical laws.

Consciousness always 'contains', as it were, some subjective experience content. For example sensory perceptions, physical and/or emotional feelings, memories, fantasies, reasoning, expectations, desires and dreams. These contents may in principle also remain unconscious, stronger, there are no indications of intentional content that were not before, at the same time or after unconscious.
In any case the conscious contents belong to subjective experiences, and the latter to the more general, psychological contents. We can establish that our conscious sensations not all come down to the same thing, they can have countless differential properties. We can look however for main lines, the dimensions or categories of mental content. Then first and foremost we'll find the sensory modalities and submodalities. These modalities we experience subjectively in qualities such as image, sound, feeling, taste and smell.
Of course we can trace back the sensory categories with the help of scientific knowledge (particularly physics) to certain characteristics and laws in the physical domain. For example, what we in general, subjectively and intersubjectively, perceive in the visual modality as the color 'red' appears to coincide with certain measured values of light waves i.e. electromagnetic radiation, in the visible spectrum, namely one wavelength of roughly 627 to 780 nanometers respectively 478 to 384 teraHz. It is clear however that we don't need that knowledge at all to experience the qualia of our mental contents, like the 'redness' of red. Moreover, although those physical laws may be well descriptive for the processes in external empiricism, they are not, and certainly not directly, relevant to our immediate subjective perception.


Indirect relationship between modalitiesof subjective psychic contents and neurophysical processes.

We can thus make a division, or mapping, of conscious contents to their corresponing neuronal-related dimensions, like sensory channels, i.e. sensory and somato-sensitive modalities, systems and circuits. These, in turn, are clearly correlated with specific neuroanatomical and physiological components in peripheral and central nervous system, such as sensory organs, neuronal cell types, fibers, tissues, and trajectories, synaptic receptors, transmitter molecules, ions, brain waves, locations, and functional areas of cerebral organs like thalamus and cerebral cortex, etcetera.
Therefore, all indicates that the substantive subjective experiential features - i.e. characteristics of conscious content - are constructed through neurophysical processes in the central areas of the cortex.
Ironically, however, it's precisely there, that we still can not find them at all through empirical observation.
The relationship between these neurophysic processes and consciousness thus has to be highly indirect concerning experiential content.
{Nb. See inter alia the "Binding Problem", the "Upshot Problem", the "Qualia Problem and other tantalizing riddles, mysteries and issues. }


Indirect relationship between form aspects of subjective mental contents and physical characteristics.

The content of conscious perception has all sorts of other form aspects or quantitative aspects. Some subjective form aspects of consciousness have a strong resemblance to physical properties, and that counts first and foremost for the totality of our subjective experience at virtually any moment of daily conscious wake functioning. This totality is also known as the so-called ' Bubble of Perception' (D. Gordon, 1984), or the "Cartesian Theatre (a.o. Dennett & Kinsbourne, 1992b, pp.234-247).
  • In the visual and kinesthetic modality this is this characterized by a certain spatial volume. It thus basically seems to be a kind of "pseudo-physical space". which can only be experienced in a exclusively subjective and exclusively individual way, but which, nevertheless, is very widely familiar as a type of phenomenon, and has a number of typical characteristics that can be recognized by almost everyone on the basis of purely conscious subjective experience. This spaciousness for instance is clearly related to the physical position and contours of one's own body. But this relationship is yet again not without peculiarities. We usually experience this space as a multiplicity of the physical volume of the brain (which in itself is curious): at least as far as the horizon of our sensory perception reaches out at the same time. At times she can be quite outstretched: for example when overseeing a clear view down from a plane, or when so-called "flying" that we can experience in lucid dreams.
    In addition, it has in general, in our experience, a kind of spherical, oval or dome shape, with strong (visual) transparency, a certain lucidity.
  • In the auditory modality there is first and foremost awareness of time, or chronology (e.g. in relation to the day and night cycle).
The contents of this intra-psychic 'space-time' can be are related with external environmental observations as well as internal sensations (like memories, thoughts, feelings, etcetera).
Properties like these clearly bear a certain relationship of resemblance and correlation with dimensions of physical reality, but we can hardly persist that they "are" physical in the same way.

Extra features (quasi-physical).

A mental representation, like a reasoning, fantasy or dream, no matter how intense, vibrant and compelling, simply obeys to quite different laws and ordering principles than external empiry, c.q. the physical domain. Herein lies the precise difference between fantasy and reality. The subjective experience seems to be of a virtual nature par excellence, and in terms of content and scope quite flexible, pliable and stretchy, depending among others on the scope of conscious attention, and freedom of nchoice with respect to selfcontrol. We can thus for now better consider conscious perception as 'quasi-physical'.

Missing features.

Moreover, consciousness typically lacks certain physical properties, which are otherwise quite common in the material universe, such as mass, electrical charge and the like.
{Nb. Absence of physical properties can, however, in principle also apply to some situations in physical reality, like a so-called "absolute vacuum". Although in that utter emptiness still certain things seem to take place in the form of spontaneous and haphazard appearance and disappearance of subatomic particles, radiations or energy packets, the so-called quantum fluctuations. Such exotic eccentricities which occur on a subatomic or astronomical scale nevertheless remain of quite a different order than the already puzzling characteristics of the most ordinary everyday experiences in consciousness.}


Network structure in conscious thinking and decision making.

The 'behaviour' of conscious processes such as thinking and deciding may well take place in accordance with the general system of signal processing in the nervous system, which resembles a network structure (neural network , neural net).
We can empirically recognize this network structure from the quick divergence and convergence of chemical and electrical signals, such as neurotransmitters and action potentials in the nervous system (to be made visible using scanning techniques such as EEG, MRI, PET, CAT, etc.). The point is, however, that these characteristics can also occur in unconscious psychic processes, including subliminal cognitive processing. So again it turns out that similarity, co´ncidence or correlation of certain neuronal properties provides insufficient grounds to assume a causal or other derivation relationship with consciousness.

(I.2) Non-unique characteristics which are related to information.

Next we take a look at the non-unique characteristics of consciousness that are related to information aspects.
This concerns in particular aspects of structure, coding, Information and information processing.
We can divide the category of non-unique, information-related characteristics into two groups.
{Nb. This does not concern the group of characteristics that, at face value, also seem to be related to certain neurophysical properties, as mentioned earlier (under 1). Instead, we will now focus on the group of characteristics which (seemingly) not per se needs to have such a relationship with neurophysical aspects.}

(I.2.1) Information related features of consciousness of reflective nature

(also valid for neuro-characteristics).

These are characteristics of consciousness, related to reflective information. That means they're a "reflection" of certain arrangements in the physical domain, most notably in the nervous system. Examples of this:

Gradual Difference.

Or difference 'of the first order' (Bateson, 1970). That is any 'significant' deviation of utter noise or random variance (signal-to-noise ratio), so it's a gradual difference, continuous and analog in nature. The detection of this type of difference depends on arbitrary sizes, scales and criteria for 'significance - and so it is not unequivocally determinable.
We can easily establish that the nervous system pre-eminently works with distinctions, and also that, as a general rule, during conscious episodes more striking patterns are detectable in brain activity.


Change: phenomena with process character.

This concerns in particular the ongoing variation in conscious processes. These may be related to the varying patterns of neuronal 'impulses' or 'signals'.


Statistically detectible coherence.

For example correlations between different neuronal processes.


Ranking of physical phenomena.

In particular arrangement of neuronal processes to space and time coordinates.

These information-related properties will often go hand in hand with consciousness, and therefore be more or less inherent to consciousness. That is: even on a physical level the episodes of consciousness are generally accompanied by reflective or inductive information patterns. But it's clear that they can occur virtually with all possible physical phenomena in the universe, and thus are far from unique to consciousness.

(I.2.2) Information related characteristics of consciousness of abstract nature

(independent of neuro characteristics).

Further we have the non-unique, information-related characteristics which do not necessarily have to be related with certain neurophysical characteristics. That is, they can be found in certain ways in neuronal processes, but at the same time it's possible to find them in certain artificial forms, such as the editing processes of automats, computers and robots.
These are characteristics of consciousness, that are closely related to abstract pattern information. This information consists of abstract content (concepts, structure images, mappings). This category concerns fairly clear structural characteristics.
Abstract pattern information has as intrinsic characteristics for example:

Unequivocal difference.

This kind of difference is called difference "of the second order" (G. Bateson, 1972).
It follows logically from distinctions and ordering patterns that have already been pre-accepted - some particular frame of reference, context or scenario, that has become 'fixed' - and it is discontinuously, discreet and digital in nature. The detection of this type of difference does not depend on arbitrary sizes, scales and criteria for 'significance' - and therefore it is unambiguously decideable.


Discrete information units.

This information consists of demarcated, discreet units, it exhibits as it were a "pigeonhole structure".


Syntactic coherence.

The ordering relationships within this type of information are typically 'syntactic' in nature. They have as such no inherent meaning of themselves, and are not bound to a certain specific or fixed interpretation.



Because of her syntactic nature this information is also not bound to a specific (physical) 'raw material', a carrier or medium. As a result, this information the property of Multiple Realizibility.


Not physically reducible.

This type of information is not reducible to physical domain. We may rightfully say that In this respect she is immaterial.
{Nb. For the substantiation of this assertion: Dimensions of information. Data from different sources and levels.}


Sequential organization of information.

Because of the aforementioned properties this information can be encoded one-dimensionally. This implies for example the possibility of "linearization" (Chafe, 1970), that is applied by natural language ability in the construction of language structures.
{Nb. Language makes primarily use of sound, is therefore heavily dependent on the dimension of time for the encoding of information about the multi-dimensional world of experience, and as a consequence, is linear, sequential in nature See for these and other effects of linguistic coding: Limitations of human knowledge and judgment - The influence of translation on information. }



The foregoing leads to the consequence that this type of information is countable and measurable: it is quantifiable . Two sub-forms count:

Quantitative information capacity.

The quantity that is represented by information is calculated from the number of possible combinations: i.e. (syntactic) complexity, maximum combinatory volume, data volume, and memory capacity.
(Less exact, for being analog measures, are displacement velocity, processing speed).

Quantitative information content.

This is the quantity of excluded alternatives, or positive entropy, substantial information storage.


Availability for analytical information processing.

This information is basis of processes of "formal intelligence", which includes abilities like combining, reasoning and arithmetic. These include induction and modelling, logical analysis and deduction, causal explanation and prediction, verification and falsification, etcetera. This includes possibilities as feedback and recursivity.


Immunity for qualitative difference.

This kind of information is, on the other hand, inherently "qualitatively neutral", in other words, qualitatively irrelevant.
A process in which quality arises out of quantity a so-called "emergence", is very hard to imagine. This of course concerns in principle a reduction problem.
From a general materialist view, this process should be causal. And indeed, the concept of emergence suggests this, although somewhat vagely, if not mystifying.
However, causal processes are typical - if not unique - to the domain of physical phenomena. The domain of quality (information) only contains relations of logical combination and derivation. The domain of quality (subjective awareness), on the other hand, only contains relations of associative combination within the 'virtual' space-time of consciousness. Neither of the two domains concerned shows any sign of causal processes, or any laws, mechanisms or dynamics of causality for that matter.
Of course, we may suppose that at least a factor is required that directly delivers a qualitative contribution or component to some quantity. But this assumption only shifts the question to the precise workings of that factor, and the origin of that contribution, and the realization of its effect.
The conclusion must be that no trace can be found as yet of a solution to this reduction problem.

In view of the foregoing it appears that abstract information patterns have their own unique characteristics, that cannot be traced back to the physical domain, but maybe also not completely to conscious domain. However, the latter is not yet a foregone conclusion. In case this does succeed, then we can of course categorise the unique characteristics of information among characteristics of consciousness.

(I.2.3) Information-related characteristics of consciousness of content nature.

These are characteristics of consciousness, related to subjective information.
Subjective information belongs to content information. This information is in any case not neuronal or otherwise objectively, empirically demonstrable. She is completely dependent on subjective interpretation or a "cognitive agent " (cognizer).
(See hermeneutics, semiotics, domain analysis, and so on).
What's more, she's at least indirectly depending on consciousness.

A subjective reference point.

An observational position, a reference point or point of view.
{Nb. Cf. the 'first person point of view (of the agent)' in Searle, 1980a, p.419-420; 1980b, p.451; 1980c, p.421; 1987a, p.145; 1992, p.20; resp. ontological subjectivity'. in Searle, 1989b, p.194; and Velmans, 1997.}



That is, recognition of difference, distinction.


A a coherence (coherence) exists in subjective perception.

The interconnection of content (coherence) becomes apparant from aspects of continuity, wholeness and unity. This coherence gives structure to mental contents. That structure is needed for subjective matters, such as 'understanding', 'insight', 'knowledge' or 'knowing' and the like, with regard to situations or situations. Again applies that such mental contents and their structural characteristics can very well also be unconscious, more specifically in the form of state characteristics of neurophysiological substances, structures and processes. And of course the concept of coherence has no meaning whatsoever at the physical process level.


Referring function.

Coherence creates the possibility of subjective referral relationships, or meaning relationships between content data.


Functiuonal to meaning.

The relationships of meaning determine the extent to which actually can be referred to matters, so-called intensionality, or aboutness.


Consciousness relates to 'higher' intelligence.

Within consciousness, among other things, processes take place of information processing; via perception, cognition and rational thinking: like logical analysis, modeling, deduction, prediction or expectation, planning and behavioural control.
Consciousness is strongly related to memory tasks, such as learning processes and retrieving or re-activation of data and reaction patterns. Consciousness is in particular connedted to contents of the so-called Short Term Memory (STM), which can be compared to the dynamic or virtual 'internal memory'. of computers. Such content are exchanged with content from the unconscious Long Term Memory (LTM), which can be compared to 'fixed' memory bansk of computers like hard disks, CDs, DVDs, pen drives, etc.).


Consciousness mainly relates to the end result of psychological processes.

Consciousness is apparently a gathering point of 'summarizing' data from pre-conscious processing.


Conscious processes are concentrated and focused in conscious attention.

Conscious attention serves as a special focus, it acts as a kind of 'internal spotlight'.
Processes under conscious attention are characterized by sequential processing.
The 'concentration' in thinking depends on all kinds of variable characteristics of the attention: gradations in convergence, mobility (volubility), distribution, firmness (stability) and steerability.
{Nb. That last characteristic, controllability of conscious attention, is actually one of the characteristics of 'free will'. See under category (3b) of characteristics.}


Potential of self-reflexive cognition.

The conscious sensation process is in principle prone to a self-reflexive ability. As a result the possibilities arise of self-referential perception, cognition, valuation and evaluation. This is for example necessary for the formation of a self-concept or 'self-image' (Concept of Self , see below). However, these processes can of course also take place unconsciously.
{Nb. This is at's beside the point to what extent the content of a self-image can apply as 'objective' or even 'meaningful'.}

Reference is hereby made to various types of modelling and information processing in human thought. We can think on several cognitive functions in this regard:

World Model.

The formation of a general world model, as a kind of virtual mirror version of reality.
As is well known, the world model has been built from abstractions such as generalizations, simplifications, stylizations and symbols.


Knowing the known.

'Knowing what you know' is useful for independent checking or testing if there's anything you already know, or already have in memory (self-reflexive cognition).



The ability to perceive or observe oneself, own's own appearance and external reactions (via self-reflexive perception).



The formation of an internal representation of oneself, a self-presentation, self-image, or concept of self' (or 'autobiographical self', according to A. Damasio, 1994).
"Perhaps consciousness arises when the brain's simulation of the world becomes so complete that it must include a model of itself" (Richard Dawkins, 1976).
Again, this self-image can stay in principle completely or largely unconsciousness, as appears to be the case with lots of people.



Testing new self-observations to the built up internal self-image: by means of self-reflexive recognition.



Conscious perception offers the possibility of introspection: observing one's own "internal" subjective sensations and processes.



The development of the idea of an own "I", self or identity, the realization that one is somebody: a conscious self-awareness. This arises partly on the basis of awareness of the self-image mentioned above (see a5).



The use of language including the ability to think in language, and to consult and discuss with oneself inwardly through the so-called 'internal dialogue'.

Here we see a series of steps in increasing subjectivity, abstraction and complexity. Thought is that consciousness would arise in particular out of the most advanced forms of mental representation.

Typical properties of information-related features.

When we now make a global comparison between the neuronal correlates of consciousness and the information-related characteristics, then some notable differences stand out. The latter category concerns fairly clear structural characteristics. They have a number of typical characteristics in common, so-called unifying properties:

They are fairly easy to recognize and describe.

As a result, they can in principle be analysed logically, and thus are well formalizable, and often even quantifiable. We can also draw up reasonably sharp agreements and rules about it, such as definitions and formulas.


These are characteristics of the way in which phenomena, events, objects, etc. can be arranged in space, in time or to other dimensions, quantities, scales or criteria. However, this arrangement can in principle easily be transferred from one thing to an other. Structural characteristics are therefore in principle not bounded to a specific carrier - of a material or immaterial nature (the aforementioned Multible Realizability).

Not uniqueness of information-related features.

There are thus all kinds of information-related properties, as well as certain neurophysical characteristics, that often go hand in hand with consciousness. For many of these characteristics a strong, positive correlation with consciousness seems to apply. But also these characteristics have not been demonstrated either to be always present with consciousness, so inherent in consciousness; or not to equally apply to other, i.e. unconscious phenomena and processes, in other words, to be unique for consciousness.

For the aforementioned 'meta properties', inherent of information-related characteristics, it has been proved possible to a certain extent to successfully imitate (simulate) processes of human information processing in artificial form, for example in machines, automatons, computers, robots. But that makes them even less unique to consciousness.
Information-related aspects therefore have their own, unifying and unique meta characteristics. And precisely because of the nature of these meta-characteristics a unique character of information-related aspects of consciousness is far less likely than in the case of the aforementioned neuro-characteristics.

When we consider some characteristics of the neurophysical and the information category in combination, certain characteristics are likely to appear of the nervous system as an intelligent system. However, these are also not necessarily unique characteristics of consciousness: because intelligent processes - in the sense of complex information processing with highly valid results - can obviously also take place unconsciously, within the nervous system, and moreover in the entire organism, in every living cell and even in the most primitive form of life.
{Nb. There's even talk of a kind of self-employed or leading internal entity, an "unconscious mind", a "personality part" or "ego-state that can operate independently outside consciousness as a regulating, reasoning and deciding internal authority, a kind of 'internal zombie' or 'zombie within'. (cf. David Chalmers's website).
About dissociation and unconscious processing, cf. e.g.: A. David Milner & Melvyn A. Goodale, 1991; 1993; 1995; 1998.}

The information-related characteristics therefore do also not belong to the unique characteristics of consciousness. Until now, the neuronal correlates basically have "the best papers" to act in a reductionist explanatory model of consciousness.

II. Uniquecharacteristics of consciousness.

As said before, it's conceivable that consciousness also has real unique characteristics. We will now first identify a number of possible candidates for such characteristics, and then address the question whether it's actually possible and meaningful to identify features unique to consciousness.

Now when can we say whether a characteristic is unique to consciousness? This must then be a characteristic that is not, or at least very hard, to be discovered just in another area, like in forms of matter or information. Truly unique characteristics of consciousness will never be present without the presence of consciousness. Thanks to this property they can serve for a clear delimitation (a cesure or demarcation) of the field of consciousness relative to the area of unconscious or extra-conscious phenomena.

The candidate unique characteristics of consciousness can be divided into two groups: a group related to relatively ' passive' experience, and a group related to relatively 'active' properties.

(II.1) Unique characteristics of consciousness that are relatively 'passive'.

These characteristics relate to the receiving end, the input or "perception side" of the psychic process: the perception of incoming data from sensory perception, body sensation, memory, association and the like, which consist of impressions, perceptions and concepts.
For example:

Overall intensityof consciousness.

This can vary from more or less awake, lucid, vivid, to calm, numb, drowsy, and the like. The intensity of consciousness locally reaches a 'peak' level in the conscious attention.
(Consciousness, however, includes not necessarily the most active psychological content - which might as well be unconsciously manifest).


A gradual convergence in the intensity of conscious attention.

In other words, the 'spearhead' structure of conscious attention. This in contrast to the more differentiated and fragmented, divergent and simultaneous unconscious processes.


Subjective sensations (sentiency).

All contents of the 'phenomenal field'. This concerns mental contents, or subjective sensations. These retain their differential qualities, that partially correspond to sensory modalities (see above, under 2a). Thus we experience in consciousness images, sounds, feelings, smells, tastes and the like.


Experience quality (experienced qualia).

For example sensory quality such as luminosity, redness, melody, heaviness, heat, hardness; 'emotional value' such as mood, "atmosphere," pleasure; emotional quality such as fun, disappointment, sadness, glee, love, endearment, anger, trust, fear, and the like.
{Nb. These different types of perception quality can of course have various hybrid forms, overlaps and mixtures.}


Experience intensity (impression).

This is about the force, depth or 'affective' intensity of experience: like neutral, 'flat', pervasive, 'sharp' and the like.


Experienced usefulness (pregnancy).

The degree of recognizability, familiarity, clarity... of a conscious representation or a perception.


Experienced meaningfulness.

(intensionality, cf. John Searle).
The degree of (un)importance, impressiveness, which does not result directly from the experience intensity, but out of the content implications and connotations.


Overall quality experience.

The degree of well-being or satisfaction: happiness, versus suffering ...

(i) op het verloop van het eigen denken, voelen en reageren.


Forms of conscious self-reflexivity.

These differ from the aforementioned possibilities of self-reflexive cognition in respect that they are consciously experienced.
For example:

Conscious introspection.

For example: conscious 'supervision' in the course of thinking, feeling and reacting.

Conscious awareness of conscious knowing.

The ability to consciously know or notice that one has a conscious awareness of something: a self-reflexive awareness of consciousness. After all, we can 'observe' directly within our consciousness what we ourselves - consciously - think and feel. And next we can realize that we're 'watching' this consciously.

Conscious self-awareness.

The conscious experience or noting that one is a "self". an individual, person, etc.., with their own, unique subjective perspective or point of reference. An "I-feeling", "Self-feeling", "Me-awareness, ( self-awareness).
{Nb. Cf. the so-called Homunculus problem, or Cartesian Theatre problem.}

(II.2) Unique features of consciousness that are more 'active'.

These characteristics have to do with the "reaction side" of the psychic process, and are therefore closely related to specific forms of (conscious) appreciation, 'colouring' or control: processes like conscious appraisal, preference, choice formation, will-decisions and more or less effective self-steering.
For example:

'Dynamic' properties of conscious attention.

For example direction of movement, frequency and speed of movement (agility, volubility), change of focus range ( focus).


Components of 'free will' (voluntarism).

Furthermore, for consciousnes various unique characteristics of 'free will' apply (voluntarianism).
This is in itself a wide-ranging subject, in short we can distinguish the following aspects and ingredients:
(1) Conscious awareness of a range of available choices or options.
(2) Experience of a certain room for conscious choice.
(3) Formation of subjectively preferred value (appraisal, appreciation, evaluation, preference), determining the extent of (in)desirability.
(4) Formation of a conscious target outcome, objective, intent, motive (intensionality).
(5) Conscious concept formation, selection, eventually also planning, of a desired action or operation.
(6) Conscious decision, will, or "free choice".
(7) Actually operational conscious self-management (with feedback-guided modification).
(8) The conscious choice to recognize one's own freedom of choice: taking responsibility.
(9) Conscious meta-evaluation: a conscious retrospective evaluation with respect to one's own evaluations, and thus considerations, goals, choices, reactions and conduct.

In any case, it is reasonable to say that the characteristics listed here are of a completely different order than the aforementioned properties in relation to physical and abstract phenomena.
{Nb. Cf. the Knowledge argument: consciousness has certain properties, such as the subjective experiential content or knowledgeability of colours, which are not known solely on the basis of physical knowledge or logical insight (Frank Jackson, 1982). A common characteristic of these properties is that they are typically related to qualia}.

If we assume for a moment that there are no other important, essentially different domains in reality, it seems that this gives us plausible examples of truly unique characteristics of consciousness.

The qualification of some consciousness traits as 'unique' does call for a philosophical nuance. We do not yet have to exclude the logical possibility, that there could be a reality, a so-called possible world, in which none of these characteristics prove to be unique to consciousness, and they might as well all apply to something else. In other words, we shouldn't lapse into a premature, positive assumption, implying the closure of logical options (i.e. the fallacy 'petitio principii', or "begging the question").
On the other hand, in everyday life we do not have to deal directly with the universe of all conceivable logical possibilities all of which are mutually undecided to exactly the same degree, and thus are still 'open'. We are rather dealing with a domain, or world, in which some states of affairs are more real, or at least better imaginable, and thus at least less excluded, than other states of affairs. With this context - which we generally tend to call 'reality' - we have to deal most directly and most concretely, and probably most frequently. And within this context, we have the least to do with the most unthinkable of possibilities. The latter context may therefore be considered our most relevant, i.e. primary framework for assessment.
From this last context we can also approach the question to the uniqueness of characteristics of consciousness. The first question that follows is whether it is thinkable that the mentioned characteristics, which here are considered to be 'unique' for consciousness, may also apply, to a greater or lesser extent, for unconscious, preconscious or extra-conscious phenomena. That's kind of hard to imagine, because they seem to be deeply involved and entangled in the 'essence' of what we usually understand by consciousness.
The reverse seems to be much better imaginable: the possibility that these characteristics are really only present in relation to consciousness, and exclusively play an active role in it. This also seems to be a real fact.
That's why I think that for the time being we can take the characteristics mentioned here as truly unique characteristics of consciousness - until proven otherwise.

(III) Characteristics that are both unique and inherent to conscious.

Finally is it conceivable that there are unique characteristics of consciousness which are also inherent to consciousness. These would then of course be found among the aforementioned unique characteristics.
These unique characteristics do not always have to be present at the same time as consciousness. In other words, they don't all have to be inherent characteristics of consciousness. There is a distinction at this point between the more 'passive' and the more 'active' unique characteristics. It is hard to imagine that consciousness can exist without the former unique characteristics, which mainly have to do with the perceptual, experiential, relatively 'passive' side of conscious perception (II.1). But the characteristics on the more 'active' side, such as conscious appraisal, preference, choice, will decisions and self-direction (II.2), seem to be less 'standard' and much more 'optional' present. So the relationship seems to be loosening from the level where the more 'passive' elements like subjective sensations and meaning aspects are complemented with more 'active' elements as preferred value and aspects of free will.
We can in any case find a most common factor (most general unifier) in the 'passive' unique characteristics which is at the same time inherent:

Conscious awareness.

A conscious noticing of something (on grounds of difference), the notion 'there's something'.