Revonsuo
- Inner Presence |
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Book |
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Topic |
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Revonsuo; Inner Presence |
16 |
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Conceptualize consciousness as the phenomenal level of organization in the brain. |
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Revonsuo; Inner Presence |
95 |
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Neural basis of consciousness is
realized during REM sleep. |
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79 |
Revonsuo; Inner Presence |
95 |
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Synchronous gamma-band
oscillations have been shown to correlate with consciousness in humans and
animals. |
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Revonsuo; Inner Presence |
96 |
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Synchronized
gamma rhythms have
been recorded over the neocortex during waking and REM sleep by using magnetoencephalography. |
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1 |
Revonsuo; Inner Presence |
96 |
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Gamma-band synchronous
oscillations are associated with the realization of the phenomenal level in the awake state. |
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Revonsuo; Inner Presence |
99 |
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Metaphors
of Consciousness |
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3 |
Revonsuo; Inner Presence |
99 |
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At a stage
of scientific research when there is no well-developed theory available of the phenomenon to be
explained, the explanations are often described in terms of a suitable metaphor. |
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Revonsuo; Inner Presence |
99 |
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A fruitful metaphor captures the essential features of a phenomenon in a single,
captivating picture. |
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Revonsuo; Inner Presence |
99 |
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A famous metaphor
in physics is Bohr's model of the internal structure of the
atom. The atom was compared to the solar system where several planets (electrons)
orbit around the sun (the nucleus). |
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Revonsuo; Inner Presence |
105 |
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The representation
of the world in dreams is so amazingly realistic that it is fully justified to call
it a "reality." |
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6 |
Revonsuo; Inner Presence |
105 |
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In both wakefulness and in dreaming we have similar representations of a "world" or a "reality." |
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Revonsuo; Inner Presence |
106 |
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Consciousness
at the phenomenal level
is engaged in internal "world
simulation." |
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1 |
Revonsuo; Inner Presence |
109 |
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"World-Simulation" Metaphor of Consciousness |
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3 |
Revonsuo; Inner Presence |
109 |
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The "world
simulation" metaphor captures consciousness from the first-person
point of view -- the way we subjectively experience it. |
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Revonsuo; Inner Presence |
111 |
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Consciousness
at the phenomenal level
is described as self-in-world, full immersion or presence as the you-are-there experience. |
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2 |
Revonsuo; Inner Presence |
119 |
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World-simulation metaphor of consciousness |
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8 |
Revonsuo; Inner Presence |
181 |
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The phenomenal
contents of consciousness make up a world of subjective
experience -- a world
simulation. |
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62 |
Revonsuo; Inner Presence |
181 |
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Throughout our waking and dreaming lives, we find ourselves
in the center of a phenomenal world simulation. |
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Revonsuo; Inner Presence |
181 |
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Consciousness
involves a hierarchical structure -- first comes phenomenal space, then qualities in this space, then organized
bundles of qualities, then meaningful bundles of qualities. |
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Revonsuo; Inner Presence |
181 |
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Visual shape
is the presence of an organized pattern of qualitative features in a phenomenal coordinate system. |
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Revonsuo; Inner Presence |
182 |
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The phenomenal
world is largely constituted by multitude of organized patterns of qualities. |
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1 |
Revonsuo; Inner Presence |
192 |
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Virtual Objects As Gestalt Windows and Semantic Windows |
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10 |
Revonsuo; Inner Presence |
192 |
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Phenomenal features of an object and its overall gestalt. |
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Revonsuo; Inner Presence |
193 |
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Hierarchical Organization of the Virtual World |
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1 |
Revonsuo; Inner Presence |
193 |
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Virtual world
consists of the following hierarchy -- phenomenal space, qualities, patterns of qualities,
virtual objects (gestalt
windows and semantic
windows), virtual place, and map location. |
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Revonsuo; Inner Presence |
197 |
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Binding and
the Phenomenal Unity of
Consciousness |
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4 |
Revonsuo; Inner Presence |
197 |
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One of the most conspicuous
features of consciousness is
its unity. |
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Revonsuo; Inner Presence |
197 |
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The binding problem is the difficulty
in seeing how any brain mechanisms could account for the phenomenal unity
of consciousness. |
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Revonsuo; Inner Presence |
207 |
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Binding and
Phenomenal Disunity I -- What Visual Disorders Tell Us about Consciousness |
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10 |
Revonsuo; Inner Presence |
207 |
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Gestalt psychologists discovered several "laws" or principles that the visual system uses to organize the content of visual awareness. |
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Revonsuo; Inner Presence |
207 |
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Visual perception groups basic elements in the phenomenal visual field in such a way that those
elements are experienced as perceptual units that naturally belong together. |
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Revonsuo; Inner Presence |
208 |
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As a result of the principles of
perceptual organization, we
are in our conscious visual perception surrounded by a world of coherent bundles of qualitative features: virtual
objects (Gestalt windows). |
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1 |
Revonsuo; Inner Presence |
208 |
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Patients suffering from apperceptive agnosia have widespread brain damage in the occipital cortex and surrounding regions;
a typical cause of the damage is carbon
monoxide poisoning. |
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Revonsuo; Inner Presence |
227 |
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Binding and
Phenomenal Disunity II -- Objects in Space |
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Revonsuo; Inner Presence |
227 |
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As we serially scan our
surroundings, not only do the elementary features of
objects become bound
into coherent entities, but we instantaneously
know what kinds of objects are present. A separate object activates a coherent
network of semantic
knowledge. |
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Revonsuo; Inner Presence |
227 |
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We not only
see a coherent bundle of features ("Gestalt window"), we see it as a representative
of a specific category of objects ("semantic window"). |
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Revonsuo; Inner Presence |
228 |
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To transform a Gestalt window to a meaningful virtual object requires semantic-conceptual binding. |
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1 |
Revonsuo; Inner Presence |
228 |
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Location Binding and the
Space around Us |
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Revonsuo; Inner Presence |
229 |
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We not only immediately see the shape and identity of an object, we are also aware of its position in relation to our body and to other
objects in the scene. This is a location
binding. |
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Revonsuo; Inner Presence |
235 |
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Split-Brain
Patients |
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6 |
Revonsuo; Inner Presence |
239 |
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Binding in Dreams |
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4 |
Revonsuo; Inner Presence |
239 |
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Binding and Dream Bizarreness |
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Revonsuo; Inner Presence |
239 |
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In the dream
world we often experience unusual combinations of perceptual
features forming novel, creative, even absolutely
crazy or nonsensical wholes. |
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Revonsuo; Inner Presence |
239 |
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Dream
experiences reveal how
binding mechanisms in
the brain go awry during sleep. |
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Revonsuo; Inner Presence |
242 |
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Failures of Semantic-Conceptual
Binding in Dreams |
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Revonsuo; Inner Presence |
246 |
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Mechanisms of Bizarreness in Dreams |
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Revonsuo; Inner Presence |
252 |
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Dreaming brain reveals how the phenomenal level is put together even in the absence of sensory
input. |
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6 |
Revonsuo; Inner Presence |
252 |
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In the dreaming
brain, phenomenal features are bound to locations in simulated space; object parts are bound together to construct integrated simulated objects; objects and persons are recognized and identified as particular objects and persons;
they are temporally continuous and embedded in the overall spatial context of the phenomenal world. |
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Revonsuo; Inner Presence |
253 |
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Specialized modules produce the Gestalt windows, the of phenomenal surrogates of objects, almost flawlessly. |
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1 |
Revonsuo; Inner Presence |
253 |
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Dreaming
shows a high level of organization and may serve important functions. The physiologically normal state of dreaming may be indispensable in trying to understand how the brain
puts together the inner
simulated reality --
the phenomenal level of organization in the brain. |
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Revonsuo; Inner Presence |
255 |
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Cognitive Mechanisms of
Phenomenal Unity |
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2 |
Revonsuo; Inner Presence |
259 |
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Consciousness
and Attention |
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4 |
Revonsuo; Inner Presence |
259 |
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In cognitive science, attention has been the concept
that comes closest to consciousness. |
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Revonsuo; Inner Presence |
259 |
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Often "attention,"
"awareness," and "consciousness" are
treated as referring to more or less the same
thing, although their precise relation is rarely
explicated. |
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Revonsuo; Inner Presence |
259 |
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Attention
is a necessary prerequisite of consciousness. |
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Revonsuo; Inner Presence |
259 |
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The contents of consciousness equal to or fully
determined by the contents of selective attention. |
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Revonsuo; Inner Presence |
265 |
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Phenomenal Vision outside the Attentional Spotlight |
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6 |
Revonsuo; Inner Presence |
265 |
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The world
simulation metaphor claims that visual phenomenology also exist outside of the focus of attention,
and before attentional selection takes place. |
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Revonsuo; Inner Presence |
266 |
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Our subjective
phenomenal visual field is structured through attention into two parts -- the
region of focal
awareness and the surrounding
regions of the peripheral awareness. |
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1 |
Revonsuo; Inner Presence |
266 |
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A paradigm example of phenomenal experience outside attention are the regions of the visual field where attention has not
yet focused -- call them regions of preattentive
vision. |
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Revonsuo; Inner Presence |
266 |
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The preattentive
scene is merely a collection of unrecognized objects and a rough spatial layout. |
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Revonsuo; Inner Presence |
266 |
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Attention
moves across the field of preattentive visual
stuff, selecting among the loose bundles of candidate objects, choosing one to
enter the focus of attention. |
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Revonsuo; Inner Presence |
266 |
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When the
focus of attention settles on one object, it
becomes a coherent virtual or phenomenal object that can be recognized (i.e. that can open a semantic window). |
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Revonsuo; Inner Presence |
266 |
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When the focus
of attention
departs from a virtual object, it falls apart again, rapidly receding
back to the state where
it was before attention arrived. It becomes again just a bundle of loosely related features without any global shape. |
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Revonsuo; Inner Presence |
267 |
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A virtual,
phenomenal object is instantaneously
reconstructed from a few pieces of disorganized visual phenomenal stuff. But the life of an organized virtual object is short.
As soon as the spotlight of attention departs, the virtual object a shattered into pieces once more. But in some
other place in which the focus of attention has moved, another virtual object is being
created for its short-lived existence. |
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1 |
Revonsuo; Inner Presence |
267 |
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Attention seems to be necessary only for visual
awareness of coherent
objects,
but outside
focal attention, there is a whole field of phenomenal visual background, full
of phenomenal visual stuff that is not organized into coherent visual objects. |
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Revonsuo; Inner Presence |
268 |
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There is a constant
interplay between the preattentive phenomenal background,
selective attention and the focus of consciousness, and the coherently bound visual information transferred to reflective
consciousness. |
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1 |
Revonsuo; Inner Presence |
268 |
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Incoherent bundles of preattentive features can be experienced only as vague parts of the phenomenal background, before being attended. |
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Revonsuo; Inner Presence |
268 |
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We have the subjective
feeling that we are at all times surrounded by world of coherent meaningful objects, even when we do not necessarily focus on those objects or see them
as tightly bound entities. |
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Revonsuo; Inner Presence |
268 |
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When we focus
on an object,
it instantaneously becomes coherent and
meaningful;
and after we have focused on it even once, it tends to remain meaningful for us even if it
becomes just blurry figure in the phenomenal background. |
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Revonsuo; Inner Presence |
269 |
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Neural Mechanisms of Binding |
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1 |
Revonsuo; Inner Presence |
269 |
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Grandmother
cell coding,
population
coding,
and temporal
coding
are the three major theories that had been put forward to solve the neural binding problem. |
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Revonsuo; Inner Presence |
272 |
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Temporal Binding |
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3 |
Revonsuo; Inner Presence |
272 |
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The notion of temporal coding posits that one
specific cell assembly is distinguished
from others by the synchronicity of firing in all the
members belonging to the same assembly. |
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Revonsuo; Inner Presence |
272 |
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Different but simultaneously
active assemblies can be distinguished from each other by
the timing of their activity (rather than the level of activity). |
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Revonsuo; Inner Presence |
272 |
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Synchronous activity may constitute a recurrent regular pattern or oscillatory rhythm. |
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Revonsuo; Inner Presence |
272 |
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An oscillatory
rhythm exhibits a characteristic frequency of coherent neuron
discharges at perhaps 40 Hz. |
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Revonsuo; Inner Presence |
272 |
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Wolfgang Singer, one of the main architects of the theory of temporal coding, presented several
predictions that may be derived from the temporal
coding hypothesis. |
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Revonsuo; Inner Presence |
272 |
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Spatially
segregated neurons should synchronize their responses if activated by features that can be grouped
together to form one
perceptual unit. |
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Revonsuo; Inner Presence |
272 |
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Synchronization should be frequent among neurons within a particular cortical area, but it should also occur across cortical areas. |
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Revonsuo; Inner Presence |
272 |
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The probability
that neurons synchronize their responses both
within a particular
area and across areas should reflect some of the gestalt criteria used for perceptual
grouping. |
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Revonsuo; Inner Presence |
272 |
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Individual
cells must be able to rapidly change the partners with which they synchronize their responses if stimulus
configurations change and require new associations. |
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Revonsuo; Inner Presence |
272 |
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If more
than one object is
present in a scene, several assemblies should form. |
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Revonsuo; Inner Presence |
272 |
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Synchronization probability should depend on the functional architecture of reciprocal corticocortical connections and should change if
this architecture is modified.
Specifically, the disruption of synchronization should impair visual perception. |
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0 |
Revonsuo; Inner Presence |
273 |
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Synchronization of neural activity has been found to oscillate around 35 to 45 Hz. |
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1 |
Revonsuo; Inner Presence |
273 |
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Synchronization is observable among adjacent cells in the same visual area, between spatially segregated cell groups within the same visual area, between groups in different visual areas, and even between
groups of cells located in visual areas of the two different hemispheres. |
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0 |
Revonsuo; Inner Presence |
273 |
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Gestalt features of the stimulus strongly modulate synchronization. |
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0 |
Revonsuo; Inner Presence |
273 |
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Wolfgang Singer suggests that synchronization reflects Gestalt criteria for perceptual grouping (proximity, similarity, continuity, common fate). |
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0 |
Revonsuo; Inner Presence |
273 |
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Singer has suggested that neural mechanisms of synchronization are primarily
mediated by intracortical (i.e. corticocortical) connections. |
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0 |
Revonsuo; Inner Presence |
273 |
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A theoretical
model of synchronizing
connections incarnates the Gestalt criteria for perceptual grouping. |
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Revonsuo; Inner Presence |
274 |
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Synchronization spreads to all those neurons in the interaction skeleton that are both independently
activated and directly
connected by Gestalt
cues. |
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1 |
Revonsuo; Inner Presence |
274 |
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Local synchronization is easily achieved because of the perceptual
grouping criterion of proximity. |
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0 |
Revonsuo; Inner Presence |
274 |
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The spread of synchronization to neurons not directly connected with each other could be achieved by a regular firing pattern, such as oscillations within a narrow frequency band. |
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Revonsuo; Inner Presence |
274 |
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A regularly
oscillating rhythm is
essential for global synchronization between all the elements of that whole. |
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Revonsuo; Inner Presence |
274 |
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Global synchronization can be established via the transitivity
of synchronization even across several synaptic connections. |
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Revonsuo; Inner Presence |
274 |
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If each pair of two adjacent, directly connected cells are firing in synchrony with the same regular frequency, then
necessarily all the neurons participating in the
same pattern do, even ones distant from each other in the
interaction skeleton. |
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0 |
Revonsuo; Inner Presence |
274 |
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This transitivity
of synchronization is proposed to account for the
nonlocal Gestalt grouping criteria. |
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0 |
Revonsuo; Inner Presence |
274 |
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Transitivity of synchronization could create the connectedness between separated elements of the same contour of separate
features of the same object. |
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0 |
Revonsuo; Inner Presence |
274 |
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Bottom-up binding during sensory input processing must be augmented by top-down influences that have a role in establishing
perceptual wholes. |
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0 |
Revonsuo; Inner Presence |
274 |
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In Singer's theory, attention is seen as an internal, top down synchronization mechanism that is needed especially to organize
complex feature combinations. |
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0 |
Revonsuo; Inner Presence |
274 |
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Attended percepts differ from non-attended ones in that the responses of neurons coding for the
attended percept are strongly synchronized with each other. |
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0 |
Revonsuo; Inner Presence |
274 |
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Although the representation of
the perceptual whole is
realized in intracortical connections, the attentional modulation of synchronization may be realized through subcortical
connections such as thalamocortical
interactions. |
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Revonsuo; Inner Presence |
277 |
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Cortical synchronization can be observed even in anesthetized
animals. |
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3 |
Revonsuo; Inner Presence |
277 |
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Researchers Engle and Singer
have formulated specific ideas about the relationship between neural synchrony and consciousness. They propose that
there are four processes (arousal, segmentation,
selection, working memory) that may together form
the neural correlate of awareness, and that the neural mechanisms of each of these processes
involves neural synchrony. |
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Revonsuo; Inner Presence |
277 |
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Arousal is
characterized by an enhanced precision of neural synchrony and a shift to a high oscillation
frequencies. |
|
0 |
Revonsuo; Inner Presence |
277 |
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Arousal
seems to be a necessary condition of awareness. |
|
0 |
Revonsuo; Inner Presence |
277 |
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Phenomenal consciousness is always organized, which requires the segmentation of different objects from each other and the background. |
|
0 |
Revonsuo; Inner Presence |
277 |
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If only a subset of all input information is selected to
awareness, synchronization could act as a signature of those representations that will be made
globally available to
the system. |
|
0 |
Revonsuo; Inner Presence |
278 |
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Synchronization may transiently stabilize neural states so that the information can be held temporarily in
a working memory
mechanism. |
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1 |
Revonsuo; Inner Presence |
278 |
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Synchronization could be the mechanism of selective
attention and reflective
consciousness. |
|
0 |
Revonsuo; Inner Presence |
278 |
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Researchers Engle and Singer
speculate that temporal binding may establish patterns
of large-scale coherence so that cross modality binding becomes
possible. |
|
0 |
Revonsuo; Inner Presence |
278 |
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Researchers Engle and Singer
propose their overall view of the neural basis of consciousness as a hierarchy of neural assemblies bound together by neural
interactions in different frequency bands. |
|
0 |
Revonsuo; Inner Presence |
278 |
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Researchers Engle and Singer
propose that synchronization is the neural
mechanism
of all the
major aspects of consciousness. |
|
0 |
Revonsuo; Inner Presence |
278 |
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The original suggestion relating
consciousness to neural synchrony goes back to Crick and Koch (1990) when they
explicitly suggest a relationship between neural
level binding through synchronization and the phenomenal level unity of perceived objects in visual consciousness. |
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0 |
Revonsuo; Inner Presence |
278 |
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Crick and Koch emphasize the role of attention in generating coherent contents of consciousness, but otherwise there theory is quite
consistent with that of Singer. |
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0 |
Revonsuo; Inner Presence |
278 |
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Rodolfo Llinás (1994) proposed that 40 Hz oscillations subserving temporal binding are generated in thalamocortical
loops. |
|
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Revonsuo; Inner Presence |
279 |
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Much of the empirical
evidence supporting the synchronization hypothesis has been based on invasive microelectrode studies of animal subjects. |
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1 |
Revonsuo; Inner Presence |
281 |
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The temporal
coding hypothesis has
been found to be the most promising candidate to account for consciousness-related
binding. |
|
2 |
Revonsuo; Inner Presence |
281 |
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Empirical evidence from animal studies using multiunit recordings and from human
studies using scalp
recordings support the view that unified visual wholes are
constructed with the help of synchronized neural
oscillations in the gamma
band. |
|
0 |
Revonsuo; Inner Presence |
312 |
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Only those events that were consciously apprehended or perceived at the time of their occurrence can lead to subsequent conscious recollection. |
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31 |
Revonsuo; Inner Presence |
312 |
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Much of the phenomenal
visual field leaves no traces behind in the hippocampus. |
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0 |
Revonsuo; Inner Presence |
312 |
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Hippocampus is densely
connected to a multitude of different areas. |
|
0 |
Revonsuo; Inner Presence |
312 |
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The parietal
lobe appears to be most important for bodily awareness and awareness
of space. |
|
0 |
Revonsuo; Inner Presence |
312 |
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It seems that
large-scale interaction
between different
areas is required for the phenomenal level of consciousness. |
|
0 |
Revonsuo; Inner Presence |
312 |
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Mechanisms of consciousness consists of networks in the brain that connect
the diverse contents
of consciousness into one
coherent whole. |
|
0 |
Revonsuo; Inner Presence |
312 |
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The constituted mechanisms of consciousness must include an
anatomically widespread complex network. |
|
0 |
Revonsuo; Inner Presence |
313 |
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In hemispatial
neglect, half of phenomenal space
disappears.. Typically, the lesions causing neglect in
different patients overlap in the inferoposterior
parietal region. |
|
1 |
Revonsuo; Inner Presence |
313 |
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Epileptic absence seizures, general anesthesia, and NREM
sleep are all states in which the phenomenal level is temporarily disabled. All of them involve remarkable changes in thalamocortical function. |
|
0 |
Revonsuo; Inner Presence |
314 |
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Epileptic absence seizures involve a brief transient loss of
consciousness.
The cause of this loss appears to be the disruption of the high frequency
thalamocortical oscillations. Suddenly, large numbers of thalamocortical loops are recruited
to a much stronger, low-frequency (~3 Hz) pattern of
the oscillatory activity. |
|
1 |
Revonsuo; Inner Presence |
314 |
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High frequency oscillations in the thalamocortical
system appear necessary for supporting the phenomenal level. |
|
0 |
Revonsuo; Inner Presence |
314 |
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Functional brain imaging experiments on the loss of
consciousness during anesthesia also point to the importance of the
thalamus. |
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0 |
Revonsuo; Inner Presence |
314 |
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A reduction in thalamocortical output may underlie the loss of
consciousness in anesthesia. |
|
0 |
Revonsuo; Inner Presence |
314 |
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Brain imaging studies have revealed that during NREM sleep, glucose and oxygen utilization in the thalamus is radically lowered. This finding
supports the idea that the thalamic level is strongly
deactivated in NREM
sleep. |
|
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Revonsuo; Inner Presence |
314 |
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Data from various sources
indicate that high frequency oscillatory activity in the thalamocortical
network plays a decisive role in the mechanism of
the conscious state. |
|
0 |
Revonsuo; Inner Presence |
314 |
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Thalamus
forms complex feedback circuits with the cortex. |
|
0 |
Revonsuo; Inner Presence |
314 |
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Two types
of thalamocortical networks can be distinguished -- diffused and focused. |
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Revonsuo; Inner Presence |
315 |
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All visual cortical areas have their own independent
connections with the thalamus. |
|
1 |
Revonsuo; Inner Presence |
315 |
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Overall picture that emerges
from current theories is that the neural constituents of consciousness are not spatially localized in one
precise place in the brain. Instead,
they probably form a complex system of corticocortical and thalamocortical networks, each contributing some essential features to the phenomenal level of organization. |
|
0 |
Revonsuo; Inner Presence |
315 |
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Synchronous neural activity at high frequencies is the leading candidate among the potential
neurophysiological mechanisms of consciousness. |
|
0 |
Revonsuo; Inner Presence |
315 |
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Gamma band oscillatory activity is involved in the conscious
perception of unified visual objects both in humans and animals. |
|
0 |
Revonsuo; Inner Presence |
315 |
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Synchronization related to visual awareness of objects has been detected by invasive
microelectrodes as well as noninvasive scalp electrodes. |
|
0 |
Revonsuo; Inner Presence |
315 |
|
Some researchers propose that gamma-band synchronous activity in
the cortex is
necessary for consciousness. Others regard synchronicity in the thalamocortical loops and subcortical circuits as more
Important for consciousness. |
|
0 |
Revonsuo; Inner Presence |
315 |
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The anatomy
and physiology of thalamocortical connections seemed
just right for producing large-scale synchronous
patterns. |
|
0 |
Revonsuo; Inner Presence |
315 |
|
Thalamic cells show inherent oscillatory
rhythmicity, and their connections
to the cortex support both specific loops and widespread loops of coherent activity. |
|
0 |
Revonsuo; Inner Presence |
315 |
|
There are both empirical and theoretical reasons to believe that
synchronicity might
serve as a mechanism for consciousness. |
|
0 |
Revonsuo; Inner Presence |
315 |
|
Empirical evidence from a variety of sources points to a connection between consciousness and gamma-band synchronicity. |
|
0 |
Revonsuo; Inner Presence |
316 |
|
Singer (2000) proposed that metarepresentations are the higher-level neural entities on
which consciousness is
based. |
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Metarepresentations have a rich combinatorial
complexity, the ability to reconfigure themselves rapidly, and
the ability to handle contents that are completely
unpredictable. |
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Temporary association of neurons into functionally
coherent assemblies could be the way to build metarepresentations. The assemblies could be defined by synchronization. |
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Conceptually, build higher-level electrophysiological entities resembling the phenomenal objects in consciousness by using synchronicity of large
neural assemblies as the mechanism. |
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Synchronicity
could be the microlevel mechanism underlying the phenomenal
contents of consciousness. |
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Dynamic core
hypothesis (Edelman and Tononi, 2000) might
be the basis of consciousness. The dynamic core is a
cluster of neuronal groups that strongly interact among
themselves.
The cluster as a whole has distinct
functional or physiological (rather than
anatomical) borders
with the rest of the brain. |
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Where in the brain is the dynamic
core localized?
Reentrant connections in the thalamocortical
system are involved,
but otherwise it is not localizable. |
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The term "dynamic
core" deliberately does not refer to a unique, invariant set of brain areas,
and the core may change
in composition from moment to moment. |
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Master Loop Hypothesis |
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According to the master loop hypothesis the neural substrate of consciousness consists of large-scale electrophysiological or bioelectrical activity patterns that are enormously complex (probably involving millions of
neurons and billions
of synapses). |
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Synchronous oscillations or other forms of spatiotemporal coherent neural activity in the large-scale networks are the mechanism by which the conscious
state, the subphenomenal space, and it's
phenomenal contents are realized in the brain. |
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The master
loop networks are characterized by an
architecture of recurrent
connectivity.
That special architecture supports closed
loops of coherent
bioelectrical activity. The loops extend "horizontally"
across the cortex (like the feedback sweep in the
ventral visual stream) and also "vertically"
between the cortex and the thalamus
("specific" and "nonspecific" thalamocortical loops). |
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Top-down constraints take the features of subjective experience as a starting
point, and try to descend from them to the features of the
constitutive mechanisms. |
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Bottom-up constraints look at neural systems that could realize large-scale
coherent states and thus be plausible candidates
for mechanisms of consciousness. |
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Evidence for the neural basis of consciousness comes from many different empirical and theoretical sources. When the sources are
integrated, a converging picture starts to emerge. Regarding the neural
correlates of visual
consciousness, the primary
visual area and the frontal
cortex seem to be not
necessary. |
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Parietal areas are necessary for the body image and the self. |
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A network of
thalamocorticosubcortical connections seems necessary for phenomenal
space and for the
state of being conscious. |
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Coherent
neural activity at high
frequencies in the thalamocorticosubcortical areas is
the prime candidate for the physiological
mechanism that might constitute
consciousness. |
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The phenomenal
level is not localized in any single cortical
lobe, but involves a large distributed network of recurrent neural activities in corticocortical and thalamocortical loops. |
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EEG abd MEG signal sources.
(diagram) |
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Functional brain imaging with PET and fMRI. |
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Neither PET nor fMRI detects electrophysiological or bioelectrical signals. |
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PET detects
gamma rays that originate when a positron is
annihilated in the brain. The positron is generated when a radioactive isotope in the tracer compound (e.g. a radioactively labeled water or glucose
molecule) in the bloodstream
decays. |
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In fMRI, it is the relative amount of oxygenated vs. deoxygenated blood
that is being detected, for these two forms display slightly
different magnetic properties. |
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The vascular
supply where fMRI
response is realized is regulated at a spatial
scale (0.5 -- 1.5 mm in
humans) that is several orders of magnitude larger than individual
neurons. This fact limits the ultimate
spatial revolution achievable
with fMRI. |
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PET and fMRI images are not images of
neurons or neural electrical activity, but of changes in the circulatory system in the brain. |
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In the temporal
dimension, when neural
activity increases in a location, there is a delay of several seconds before blood flow increases. The fMRI signal starts at two seconds and reaches its peak at about 13
seconds from the stimulus
onset. |
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The colorful computer-generated
images produced by PET and fMRI are not "images of the
mind" or even "neuroimages," but rather images of blood flow or blood oxygenation levels in the
brain. |
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Structural MRI images mostly reflect proton densities of different tissues and give good spatial resolution and contrast between different tissues. |
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Consciousness,
or the phenomenal level
of organization, probably resides at higher levels of complex electrophysiological and bioelectrical phenomena in the brain. |
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Global patterns of organized bioelectrical
activity that constitutes the phenomenal level change in about
the rate of once in 100 to 300 ms. |
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Synchronous oscillations on which the phenomenal level is based at the underlying microlevels are probably within the
gamma range (20 -- 80 Hz). |
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The temporal
resolution of the data
recording must be at least as high as the rate of reorganization of the phenomenal level. |
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What is the spatial
scale in which the subjective just-noticeable
differences of spatial location are realized within the phenomenal level? We may speculate that it must be courser
than the spatial scale of single neurons, but certainly much
finer than the scale of 1 mm3. |
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An ideal
neural signal data recorder would sample data at the rate of 100 Hz, and could resolve spatial details of
activity in volumes of space around 10-4mm3. |
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An ideal
neural signal data recorder would collect signals
at the levels where organized electrophysiological
patterns are realized in recurrent loops of coherent activity. |
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An ideal
neural signal data recorder would collect signals
from a wide range of different frequencies across the whole brain, especially in corticocortical and thalamocortical loops. |
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A living
organism as a unified
whole cannot be described in the language of chemical formulas. |
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Objective neural mechanisms and subjective consciousness can be seen as a line along the same
gapless continuum. |
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Neuroscience
will have to be a rationalized with a phenomenal
level as an integral part of the biological brain, and the empirical data must be phenomenalized and subjective consciousness itself
used as the domain of theoretical modeling. |
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Consciousness
and neuroscience must
meet across the explanatory gap, each coming halfway to meet the other. |
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Consciousness
surely seems to make an enormous difference in our behavior. |
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Blindsight
-- patient does not see anything in the blind part of the visual
field, but somehow the behavioral
responses are influenced
by the unseen stimuli. Blind regions in the
visual fields result from brain injury to the primary visual cortex (V1). |
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Prosopagnosia
-- inability to recognize familiar people from their faces. |
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Unilateral neglect -- dramatic loss of awareness of one side of space, remains a mystery, because the primary
sensory pathways may still be intact, and yet the patient is not aware of the stimulus. |
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Biological Function of Dreaming |
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Converging evidence from a wide
variety of sources supports the view that the nocturnal
world simulation we know as "dreaming" is functionally specialized in the simulation of dangers and threatening events. |
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