Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Attention Mechanisms


Ascending Arousal System divides into Two Major Branches

Ascending arousal system divides into two major branches at the junction of the midbrain and diencephalon.  One branch enters the thalamus, where it activates and modulates nuclei with extensive diffuse cortical projections.  Other branch travels through the lateral hypothalamus area, joined by other cell groups, all of which diffusely innervate the cerebral cortex. (Kandel; Principles of Neural Science, 897)

Three Interacting Networks mediate Attention

Three interacting networks mediating different aspects of attention:  (1) a posterior attention system comprising parietal cortex, superior colliculus, and pulvinar that is concerned was spatial attention; (2) anterior system centered on the anterior cingulate in the medial frontal lobe that mediates target detection and executive control; (3) a vigilance system consisting of the right frontal lobe and brainstem nuclei, principally the noradrenergic locus coerulus (LC). (Parasuraman; Varieties of Attention, 236)

The form of awareness associated with focal attention is caused by the firing of a temporally coordinated assembly of neurons firing in some special manner for at least 100 or 200 msec. This special form of neuronal activity induces short-term memory. (Koch and Crick; Neuronal Basis, 109)

Wakefulness is a dreamlike state modulated by specific sensory inputs. (Llinás; Perception as Oneiric-like, 113)

The five senses gather much more information than the human brain is able to process.  We must have a facility to ignore a lot of what is happening around us. (Andreasen, Creating Brain, 103)

Function of attention is to focus the neural resources for recognition on a specific region within a scene. Salient areas of a scene can often be defined on the basis of relatively low-level cues such as pop-out due to motion, depth, texture, or color. (Van Essen; Dynamic Routing Strategies, 278)

Subjective experience is related to activation of the anterior cingulate attention system. (Posner; Constructing Neuronal Theories, 189)

Selective component of attention seems based primarily in dorsolateral frontal cortex. (Fuster; Prefrontal Cortex, 347)

Exclusionary component of attention, the inhibitory control of interference, seems primarily based in ventral frontal cortex. (Fuster; Prefrontal Cortex, 347)

Most of the medial frontal cortex is involved in attention and somatic motility. (Fuster; Prefrontal Cortex, 199)


Currently activated memory elements are represented as a subset of long-term memory, and the focus of attention is represented as a subset of the currently activated memory elements. (Cowan; Attention and Memory, 139)


Nelson Cowan has a model of Attention and Memory.


Reticular system, attention and arousal

Reticular system: multiple ascending pathways from subcortical nuclei, each associated with different neurotransmitters and neuromodulators that have different properties and different cortical innervation patterns. (Parasuraman; Varieties of Attention, 227)

Four main projection systems have been identified as playing functional roles in arousal and attention: (1) cholinergic basal forebrain, (2) noradrenergic nucleus locus coerulus (LC), (3) dopaminergic median forebrain bundle, (4) serotonergic dorsal raphe nucleus. (Parasuraman; Varieties of Attention, 227)

Basal forebrain cholinergic system plays an important role in attention and arousal processes. (Parasuraman; Varieties of Attention, 228)

LC noradrenergic system role in cortical arousal. (Parasuraman; Varieties of Attention, 228)


Locus ceruleus crucial for attention

Brain stem contains the locus ceruleus, crucial for attention and for cognitive functions.  Fully half of all noradrenergic neurons of the brain are clustered together in this small nucleus. (Kandel; Principles of Neural Science, 871)

Hypothesized that all neurons corresponding to various aspects of the object the observer is attention to fire in an oscillatory and semisynchronous manner, binding them together. (Koch and Crick; Neuronal Basis, 99)

Original hypothesis was that the phase-locked firing of a set of neurons at 40 Hz was the neural correlate of visual awareness. (Koch and Crick; Neuronal Basis, 101)

Various types of neural connections may be associated with some forms of visual awareness. Possible examples are: (1) Connections to the hippocampal system and the higher planning levels of the motor system, (2) direct back projections to V1 and possibly V2, and (3) reentrant connections within layer 4 or between cortical areas at the same level in the anatomical hierarchy. (Koch and Crick; Neuronal Basis, 109)


Working Memory and Attention

Close relationship between working memory and attention. (Fuster; Prefrontal Cortex, 349)

Working memory is indeed a form of attention -- sustained attention focused on an executive cognitive network for the processing of perspective action. (Fuster; Prefrontal Cortex, 349)

Frontal cortex exerts 'top-down' control that biases neuronal activity in sensory cortex toward the relevant sensory information. (Squire & Kandel; Memory, 107)

Visuospatial sketch pad as the seat of phenomenological experience of visual imagery, and the central executive as the attentional controller. (Baddeley; Working Memory, 315)

Well into adulthood, attention span increases, plans become more elaborate, goals include increasing numbers of subgoals, decision-making is more dependent on deliberation, and the capacity to use both inductive and deductive reasoning increases. (Fuster; Prefrontal Cortex, 202)

Visual attention acts as an informational bottleneck that reduces to manageable levels the amount of image data reaching high-level cortical centers involved in pattern recognition. (Van Essen; Dynamic Routing Strategies, 273)

Thalamus and Attention

A major function of the thalamus is to gate and modulate the flow of information to the cortex.

Several PET experiments with humans have shown activation of the pulvinar during the visual attention. (LaBerge; Attention, the Triangular Circuit, 302)

Our ability to filter unnecessary stimuli and focus our attention is mediated by brain mechanisms in the thalamus and the reticular activating system. (Andreasen, Creating Brain, 103)

Subcortical activating systems in the thalamus, with its rich and diverse connectivity to the cortex, have been considered a likely site for selective engagement of specific cortical functions. (Fischler; Attention and Language, 385)

Reticular nucleus of the thalamus has inhibitory connections with the specific nuclei and can select or gate various combinations of their activity. (Edelman; Universe of Consciousness, 107)

Reticular nucleus in the thalamus (nRt), with its ability to gate traffic from sensory surfaces to cortex, is one natural candidate for a selective attention mechanism. (Baars; Neuronal Mechanisms of Consciousness, 270)

Nucleus reticularis thalami (nRt) possible role in selective attention and conscious processing was pointed out by Crick (1984). Because the output of the nucleus reticularis thalami (nRt) neurons is itself inhibitory, it's activation disinhibits the sensory relay pathways; i.e. increases entry to the cerebral cortex by stimuli that are currently engaging the thalamocortical loops. (Baars; Neuronal Mechanisms of Consciousness, 272)

The controlling agent of attention is presumed to be encoded within specific areas of the prefrontal cortex (PFC). (LaBerge, "Attention, Awareness, and the Triangular Circuit," Baars, Essential Sources, 323)


Research study — Attention Gateway in Visual Thalamusattention modulates thalamic visual responses in two phases: an initial modulation that attenuates TRN responses and enhances LGN responses, followed by a slowly building later enhancement limited to LGN.

Research study — Access to Consciousnessstructured spontaneous activity in thalamocortical circuits, and its critical role in allowing or blocking access by sensory stimuli.


Pulvinar of the Thalamus

Hypothesize that the pulvinar plays an important role in providing the control signals required for the routing circuit of attentional control. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar is reciprocally connected to all areas in the form pathway, making it a plausible candidate for modulating information flow from V1 to IT. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar, a subcortical nucleus of the thalamus, makes reciprocal connections with all of the visual processing cortical areas. (Van Essen; Dynamic Routing Strategies, 285)

Hypothesize that the pulvinar plays an important role in providing the control signals required for the routing circuit of attentional control. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar is reciprocally connected to all areas in the form pathway, making it a plausible candidate for modulating information flow from V1 to IT. (Van Essen; Dynamic Routing Strategies, 287)


Research study — Attention Regulated by Thalamocortical Activity between Pulvinar and Cortexhypothesized that the pulvinar, a thalamic nucleus, regulates cortical synchrony. We mapped pulvino-cortical networks within the visual system, using diffusion tensor imaging.


Cerebellum and Attention

Cerebellum has connections to many parts of the brain involved in attention and is intimately involved with the higher functions, setting the timing and rhythm and other aspects of language, memory, and emotion. (Ratey; User's Guide to Brain, 305)

Anterior Cingulate and Attention

One brain region controlling attention that is especially concerned with holding internally generated stimuli in focus is the anterior cingulate cortex, a region on the inside front edge of the longitudinal fissure, the deep chasm that runs from the front of the brain to the back. (Carter; Mapping the Mind, 195)

Anterior cingulate cortex is sensitive to information from the body and it is fiercely active when a person feels pain, and also becomes active when we are conscious of emotion. (Carter; Mapping the Mind, 195)

Anterior cingulate gyrus has strong connections with a variety of other neural areas and plays a critical role in attention and what is meant by consciousness, and relates both to awareness and to voluntary control. (Posner; Constructing Neuronal Theories, 188)

The ACC has a fundamental role in relating actions to their outcomes and consequences, and thus guides decisions and choices about actions. (Posner; Cognitive Neuroscience of Attention, 313)

Anterior cingulate is active during tasks that require some thought and its activity is reduced or disappears as tasks become routine. (Posner; Executive Attention, 411)

Anatomical studies suggests that the anterior cingulate, like many brain regions, has close contact with many other cortical areas. (Posner; Executive Attention, 409)

The cingulate's connections to the lateral frontal areas involved in word processing and to posterior parietal areas involved in orienting are particularly strong. (Posner; Executive Attention, 409)

The anterior cingulate and other midline frontal areas are involved in producing the local amplification in neural activity that accompanies top-down selection of items. (Posner; Executive Attention, 411)


Attention is necessary for consciousness. (Baddeley; Working Memory, 311)

Consciousness serves as a mental workspace, a very powerful mechanism for registering the environment and relating it to past experience, which can in turn be used to model the present, and using that model, to simulate and hence to predict the future and plan further action. (Baddeley; Working Memory, 314)



In the attention model of Edmund Rolls, control is performed by the information loaded into prefrontal cortex short-term memories, biasing early visual cortical spatial and object processing areas by backprojections. (Rolls; Memory, Attention, and Decision-Making, 442)

Thalamus, a part of the ascending reticular activating system, has a central role in the conscious state and attention. (Afifi; Functional Neuroanatomy, 258)

The afferent inputs to the pulvinar circuit from various cortical areas (such as the PPC) are regarded as the controls on the circuit mechanism that can produce the expression of attention in a localized region of another cortical area (e.g. V4). (LaBerge; Attentional Processing, 175)


Research study — Attention and Awareness in Primary Visual Cortexrecent progress in psychophysics indicates that visual attention and visual awareness are two dissociated functions in the visual system.

Research study — Attention ControlAcetylcholine (ACh) levels in the brain diminish with aging: endogenous nicotinic ACh receptor-mediated cholinergic regulation of attentional performance.

Research study — Neuronal Oscillations as a Mechanism of Attentional Selectiongamma-band neuronal oscillations appear integral to visual attention; lower-frequency oscillations seem to function in the rhythmic shifting of excitability in local neuronal ensembles.

Research study — Attention Enhances Retrieval and Stability in Hippocampusformation of episodic memories depends on the hippocampus, involving the conscious recall of events that occur in specific spatial contexts; physiological basis of the interaction between attention and memory in the hippocampus.



Complex organisms, in particular those with brains, suffer from information overload. In primates, about one million fibers leave each eye and carry on the order of one megabyte per second of raw information. One way to deal with this deluge of data is to select a small fraction of it and to process this reduced input in real-time, while the non-selected portion of the input is processed at a reduced bandwidth. In this view, attention is a mechanism that selects information of current relevance to the organism while leaving the non-selected, and thus non-attended, data to suffer from benign neglect. (Naotsugu Tsuchiya and Christof Koch (2008), Scholarpedia, 3(5):4173.)


Consciousness is surmised to have quite different functions from those of attention. These range from summarizing all relevant information pertaining to the current state of the organism and its environment and making this compact summary accessible to the planning stages of the brain, to detecting anomalies and errors, decision making, language, inferring the internal state of other animals, setting long-term goals, making recursive models, and rational thought. (Naotsugu Tsuchiya and Christof Koch (2008), Scholarpedia, 3(5):4173.)


A major function of the thalamus is to gate and otherwise modulate the flow of information to the cortex. The thalamus represents the final bottleneck of information flow before it gets to cortex. For processes of attention and other behavioral requirements, evolution has established a modification and filtering of information flow at the level of thalamus before it reaches the cortex. (S. Murray Sherman (2006), Scholarpedia, 1(9):1583.)



Network model of attention

Network model (Mesulam's) of attention in which several distinct cortical regions interact, including posterior parietal cortex, cingulate cortex, and frontal cortex, all of which are influenced by the reticular activating system. (Webster; Neuroanatomy of Visual Attention, 27)

Parietal component provides an internal perceptual map of the external world. (Webster; Neuroanatomy of Visual Attention, 27)

Cingulate component regulates the spatial distribution of motivational valence. (Webster; Neuroanatomy of Visual Attention, 27)

Frontal component coordinates the motor programs for exploration, scanning, reaching, and fixating. (Webster; Neuroanatomy of Visual Attention, 27)

Reticular component (including noradrenergic, dopaminergic, and cholinergic ascending systems) provides the underlying level of arousal. (Webster; Neuroanatomy of Visual Attention, 27)

Cortical components within the attention network are heavily and reciprocally interconnected and are also connected with subcortical structures, including the superior colliculus, which is connected to the frontal eye fields and to the parietal cortex, and the pulvinar and striatum, which are connected to all three cortical regions in the network. (Webster; Neuroanatomy of Visual Attention, 27)

In addition to the intralaminar thalamic nuclei, two other thalamic nuclei, the reticular nucleus and the pulvinar, have been implicated in attention and arousal. (Parasuraman; Varieties of Attention, 227)


Spatial attention theory

Neural processes involved in spatial attention theory proposed by Mesulam. (Awh; Spatial Working Memory, 354)

Thalamus a key brain structure of attention

Key brain structure involved in attention is the thalamus, a large collection of cells located atop the brainstem in the center of the upper brain. (Hobson; Consciousness, 59)

Attention -- dopamine, 'pleasure synapses', motivation

Attention manages the relationship of the brain with the environment. Nuclei in the reticular formation participate in the fixation of attention. Dopamine neurons in the brainstem are concerned with the control of attention, in addition to their involvement in the 'pleasure synapses' that control motivation. (Changeux; Neuronal Man, 154-156)

Attention and language

Attention and language; two of the most widely studied aspects of human cognitive skills. Basic elements of cognition. (Fischler; Attention and Language, 381)

Language competes with other processes, for access to a limited-capacity executive attentional system. (Fischler; Attention and Language, 384)

Ability to represent the phonemic or orthographical pattern that corresponds to a word is the means of communication; the goal is to communicate information, and the semantic representation of the concepts that a word stands for is the heart of language. (Fischler; Attention and Language, 388)

Neural systems that represent the meaning of words have proved particularly challenging to isolate anatomically, which has led some to conclude that semantic knowledge is by its nature diffusely represented, probably by a sort of distributed processing systems. (Fischler; Attention and Language, 389)

Cell assemblies representing knowledge may be part of a distributed network. (Fischler; Attention and Language, 389)



(paraphrase of Niebur & Koch; Computational Architectures for Attention, 168, 180)


Any information-processing system with finite resources operating in the real world requires an attentive mechanism, because the multitude of sensors would overwhelm its computational capabilities if all sensory input were processed simultaneously. Efficient processing requires careful selection of the most relevant stimuli and suppression of all others.

A significant reduction of complexity is achieved if the recognition of an object (what is it?) can be separated from its localization (where is it?). Such a separation is useful because those two properties of a stimulus are often independent from each other: a given stim­ulus can occur in many different places in a visual scene and, conversely, a given location in a visual scene can hold a variety of different stimuli. That observation allows the decoupling of the tasks of recognition and localization. Computationally, therefore, the size of the required space is only the sum of the feature space and the locality space, rather than their (outer) product, which is in general significantly larger.

The anatomical and physiological structure of the primate visual system uses distinct pathways for encoding spatial information of objects in the environment and the specific features of those objects. The locations of visual stimuli are represented in the dorsal (or "where") pathway, which is also the dominant cortical pathway for any visuomotor tasks, such as controlling the eyes, reaching with the hand toward a visually identified target, visually induced body adjustments, and so forth. Detailed feature processing and object recognition are localized in the ventral (or "what") pathway. Tight integration of the two pathways is essential.

(end of paraphrase)


Attention and Distraction

(paraphrase of Hobson; Dreaming as Delirium, 166ff)


While we need to be able to engage and disengage our attention, we also need to be able to maintain our attention once we have focused on something. As a high school or college student your academic success was related to your ability to resist distraction, to pay sustained attention to your book no matter who walked into the room, such as the library, where you were studying. You had both a sharp focus and a sustained span of attention even when friends tempted you to talk or flirt instead of study.

So how do we negotiate the tug of war between attention and distraction? How do we select the signals we want to focus on and exclude the distracters? The sensory data that compete for our attention are myriad, and our selection task is, at every instant, formidable. We have eight modalities to choose from: the five senses — vision, hearing, touch, taste, smell — and three data channels that come from within our bodies — posture, movement, and pain.

Engagement is controlled by the thalamus, a deep central struc­ture in the brain. It projects messages widely to areas of the cortex and receives powerful feedback from each of them. Because of its central position and its reciprocal firing pattern, the thalamus is the ideal point at which to intercept unwanted or unexpected data. Selective attention depends as much on the suppression irrelevant data as it does on the amplification of relevant data, and the thalamus is good at suppression. By feeding no-go signals into the thalamus, huge areas of the cortex can be effectively deprived of input. In an analogy to radio, the thalamus is a very effective tuning filter for the brain-mind.

Each thalamic area is connected to a particular cortical sector. Because these connections are reciprocal, the interaction between these areas is rapid and intense. Consciousness owes its exquisite perceptual intensity and clarity to the capacity of these thalamocortical circuits to represent the world with great fidelity. The system has a built-in propensity to tune (modulate) itself, and that tuning propensity can also be enhanced voluntarily, as when we decide to re­duce other sensory inputs the better to concentrate upon those that interest us most. (Hobson; Consciousness, 60)

(end of paraphrase)


Day Dreaming

(paraphrase of Hobson; Dreaming as Delirium, 168ff)


By changing focus from external to internal, we are moving to­ward the domain of dreaming and psychosis; Attention, like all other faculties of the brain-mind, is state dependent. One key vari­able is volition. I can voluntarily shift attention only when I am awake. In sleep my attention is riveted to internally generated data. Since we now know that the state shift from waking to sleeping is achieved by the brain stem, we might better understand attention itself by exploring those bottom-up processes that shift it. Because attention has a strongly voluntary aspect, we might also learn how to gain some top-down control over the bottom-up processes that govern our brain-mind states. The payoff would then come from finding natural and scientifically valid ways to manage our con­sciousness via the selective action of attention. Self-hypnosis, control, and the plain old power of positive thinking are among the prizes that we seek.

(end of paraphrase)


Directed Visual Attention

(paraphrase of Van Essen, et al; Dynamic Routing Strategies, 278)


Purpose of attention is to focus the neural resources for recognition on a specific region within a scene. A simple strategy for an autonomous visual system:

Form a low-pass filtered version of the scene so that objects are blurred into blobs.

Select one of the blobs from the low-pass image — whichever is brightest or largest — and set the position and size of the window of attention to match the position and size of the blob.

Feed the high-resolution contents of the window of attention to an as­sociative memory for recognition.

If a match with one of the memories is close enough (by some as yet unspecified criterion), then consider the object to have been recognized; note its identity, location, and size in the scene. If there is not a good match, then consider the object to be unknown; either learn it or disregard it.

Now inhibit this part of the scene and go to step 2 (find the next most salient blob).

(end of pharaphrase)


Model of attentional processing in visual cortex

(paraphrase of Van Essen; Dynamic Routing Strategies, 285ff)


Model of attentional processing in visual cortex. Different stages of the network correspond to the major cortical areas in the "form" pathway. Two stages for V1: V1a corresponding to layer 4C, and V1b corresponding to superficial layers. Remaining areas—V2, V4, and inferotemporal cortex (IT)— occupy one stage apiece. (Van Essen; Dynamic Routing Strategies, 285)

Each node of the attentional processing model corresponds to a feature vector that represents the activity profile of a large group (hundreds or thousands) of neurons in each visual area. (Van Essen; Dynamic Routing Strategies, 285)

Neural resources in IT are probably devoted to recognition rather than representing the contents of the window of attention itself. (Van Essen; Dynamic Routing Strategies, 287)

Hypothesize that the pulvinar plays an important role in providing the control signals required for the routing circuit of attentional control. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar is reciprocally connected to all areas in the form pathway, making it a plausible candidate for modulating information flow from V1 to IT. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar receives projections from both PP and superior colliculus, which are known to encode the direction of saccade targets and may also be involved in setting up attentional targets. (Van Essen; Dynamic Routing Strategies, 287)

Neurophysiological studies, lesion studies, and neuroimaging studies of the pulvinar, suggest that it plays an important role in visual attention. (Van Essen; Dynamic Routing Strategies, 287)

Pulvinar is spatially localized while at the same time able to communicate with vast areas of the visual cortex. (Van Essen; Dynamic Routing Strategies, 287)

Relative proximity of pulvinar neurons to each other could facilitate the competitive and cooperative interactions among the control neurons that are necessary to enforce the constraint of having a single window of attention. (Van Essen; Dynamic Routing Strategies, 287)

Intrapulvinar communication could possibly be subserved by interneurons within the, pulvinar or through the reticular nucleus of the thalamus. (Van Essen; Dynamic Routing Strategies, 287)

Neural gating mechanisms are believed to play an important role in many aspects of nervous system function. (Van Essen; Dynamic Routing Strategies, 288)

A pyramidal cell may branch to several cortical areas and make synaptic connections to a multitude of neurons. (Van Essen; Dynamic Routing Strategies, 288)


Posterior parietal cortex, critical for spatial attention

The research report highlighted below reveals a neural feedback loop along the dorsal stream of visual processing. Synchronization between neurons may be a fundamental mechanism ensuring that the output from local neural networks has an increased impact on sensory areas.

The posterior parietal cortex (PPC), a higher-order structure along the dorsal stream of visual areas, is critical for spatial attention, as discussed in the following Science article. This study, which researched the neural response of monkeys, monitored the lateral intraparietal area (LIP) and the immediately earlier stage of the dorsal pathway, the medial temporal area (MT). The studies also recorded from the overlapping receptive fields (RFs) and the local field potentials (LFPs) from the two sites. If LIP has a top-down influence on MT responses during focal attention, then the phase of the coherence should show LIP leading MT. The data show that the phase of the peak coherence of the LIP preceded MT by ~4.55 ms in one test and !7.43 ms in another test. This phase relationship is physiologically plausible for feedback from the LIP to MI, assuming a conduction velocity of 1 m/s for intracortical connections.

Competition Attentional System

To limit the amount of information that is processed, a model of attention has been proposed based on neural competition. (Webster; Neuroanatomy of Visual Attention, 29)

At several points between input and response, objects in the visual field compete for limited processing capacity and control of behavior. This competition can be biased by both bottom-up neural mechanisms that separate figures from their backgrounds as well as by top-down mechanisms that bias competition in favor of objects relevant to current behavior. (Webster; Neuroanatomy of Visual Attention, 29)

The bias for attention can be controlled by selection of spatial location or by selection of object features. (Webster; Neuroanatomy of Visual Attention, 30)

When the situation is novel on highly competitive (i.e. when it requires executive control), a supervisory attentional system intervenes and provides additional inhibition or activation to the appropriate schema for this situation. (Posner; Executive Attention, 402)

Competition for these sub-processing systems is resolved by inhibition in the local neural circuit. (Posner; Executive Attention, 403)

Competition can be biased by a top-down mechanism that selects objects that are important to the current behavior all goal. (Posner; Executive Attention, 403)

Neural Mechanisms of Visual Attention — Top-Down Feedback

Attention helps us process potentially important objects by selectively increasing the activity of sensory neurons that represent the relevant locations and features of our environment.  A research study investigated how parietal cortical output influences neural activity in early sensory areas.

Visual attention tasks preferentially modulate fast-spiking inhibitory neurons, consistent with a convergence of top-down influences upon local excitatory-inhibitory circuit balance. Recovery strategies aimed at the Lynx1 interaction for (amblyopia) could be fruitful in conjunction with attentional tasks that stimulate cholinergic release (e.g., perceptual learning, video-game training).



Attention and Consciousness (Koch; Quest for Consciousness, 153, 266, 173)

Consciousness requires attention? (Koch; Quest for Consciousness, 153, 163)



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