Stephen Grossberg, Consciousness Researcher - Abstracts

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Alfredo Pereira Jr (group admin)

Date:

27 August 2007

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1 comment

1: Neural Netw. 2004 Jun-Jul;17(5-6):707-18.

Fast synchronization of perceptual grouping in laminar visual cortical circuits.

Yazdanbakhsh A, Grossberg S.

Department of Cognitive and Neural Systems, Boston University, Boston, MA 02215,
USA.

Perceptual grouping is well known to be a fundamental process during visual
perception, notably grouping across scenic regions that do not receive
contrastive visual inputs. Illusory contours are a classical example of such
groupings. Recent psychophysical and neurophysiological evidence have shown that
the grouping process can facilitate rapid synchronization of the cells that are
bound together by a grouping, even when the grouping must be completed across
regions that receive no contrastive inputs. Synchronous grouping can hereby bind
together different object parts that may have become desynchronized due to a
variety of factors, and can enhance the efficiency of cortical transmission.
Neural models of perceptual grouping have clarified how such fast synchronization
may occur by using bipole grouping cells, whose predicted properties have been
supported by psychophysical, anatomical, and neurophysiological experiments.
These models have not, however, incorporated some of the realistic constraints in
which groupings in the brain are conditioned, notably the measured spatial extent
of long-range interactions in layer 2/3 of a grouping network, and realistic
synaptic and axonal signaling delays within and across cells in different
cortical layers. This work addresses the question: Can long-range interactions
that obey the bipole constraint achieve fast synchronization under realistic
anatomical and neurophysiological constraints that initially desynchronize
grouping signals? Can the cells that synchronize retain their analog sensitivity
to changing input amplitudes? Can the grouping process complete and synchronize
illusory contours across gaps in bottom-up inputs? Our simulations show that the
answer to these questions is Yes.

Publication Types: Comparative Study Research Support, U.S. Gov’t, Non-P.H.S.

PMID: 15386904 [PubMed – indexed for MEDLINE]

2: Neurosci Biobehav Rev. 2001 Aug;25(6):513-26.

Linking the laminar circuits of visual cortex to visual perception: development,
grouping, and attention.

Grossberg S.

Department of Cognitive and Neural Systems and Center for Adaptive Systems,
Boston University, 677 Beacon Street, Boston, MA 02215, USA. steve@bu.edu

How do the laminar circuits of visual cortical areas V1 and V2 implement
context-sensitive binding processes such as perceptual grouping and attention,
and how do these circuits develop and learn in a stable way? Recent neural models
clarify how preattentive and attentive perceptual mechanisms are intimately
linked within the laminar circuits of visual cortex, notably how bottom-up,
top-down, and horizontal cortical connections interact within the cortical
layers. These laminar circuits allow the responses of visual cortical neurons to
be influenced, not only by the stimuli within their classical receptive fields,
but also by stimuli in the extra-classical surround. Such context-sensitive
visual processing can greatly enhance the analysis of visual scenes, especially
those containing targets that are low contrast, partially occluded, or crowded by
distractors. Attentional enhancement can selectively propagate along groupings of
both real and illusory contours, thereby showing how attention can selectively
enhance object representations. Recent models explain how attention may have a
stronger facilitatory effect on low contrast than on high contrast stimuli, and
how pop-out from orientation contrast may occur. The specific functional roles
which the model proposes for the cortical layers allow several testable
neurophysiological predictions to be made. Model mechanisms clarify how
intracortical and intercortical feedback help to stabilize cortical development
and learning. Although feedback plays a key role, fast feedforward processing is
possible in response to unambiguous information. Model circuits are capable of
synchronizing quickly, but context-sensitive persistence of previous events can
influence how synchrony develops.

Publication Types: Research Support, U.S. Gov’t, Non-P.H.S. Review

PMID: 11595271 [PubMed – indexed for MEDLINE]

3: J Int Neuropsychol Soc. 2000 Jul;6(5):583-92.

How hallucinations may arise from brain mechanisms of learning, attention, and
volition.

Grossberg S.

Department of Cognitive and Neural Systems, Boston University, MA 02215, USA.

This article suggests how brain mechanisms of learning, attention, and volition
may give rise to hallucinations during schizophrenia and other mental disorders.
The article suggests that normal learning and memory are stabilized through the
use of learned top-down expectations. These expectations learn prototypes that
are capable of focusing attention upon the combinations of features that comprise
conscious perceptual experiences. When top-down expectations are active in a
priming situation, they can modulate or sensitize their target cells to respond
more effectively to matched bottom-up information. They cannot, however, fully
activate these target cells. These matching properties are shown to be essential
towards stabilizing the memory of learned representations. The modulatory
property of top-down expectations is achieved through a balance between top-down
excitation and inhibition. The learned prototype is the excitatory on-center in
this top-down network. Phasic volitional signals can shift the balance between
excitation and inhibition to favor net excitatory activation. Such a volitionally
mediated shift enables top-down expectations, in the absence of supportive
bottom-up inputs, to cause conscious experiences of imagery and inner speech and
thereby to enable fantasy and planning activities to occur. If these volitional
signals become tonically hyperactive during a mental disorder, the top-down
expectations can give rise to conscious experiences in the absence of bottom-up
inputs and volition. These events are compared with data about hallucinations.
The article predicts where these top-down expectations and volitional signals may
act in the laminar circuits of visual cortex and, by extension, in other sensory
and cognitive neocortical areas, and how the level of abstractness of learned
prototypes may covary with the abstractness of hallucinatory content. A similar
breakdown of volition may lead to delusions of control in the motor system.

Publication Types: Research Support, U.S. Gov’t, Non-P.H.S. Review

PMID: 10932478 [PubMed – indexed for MEDLINE]

4: Spat Vis. 1999;12(2):163-85.

How does the cerebral cortex work? Learning, attention, and grouping by the
laminar circuits of visual cortex.

Grossberg S.

Department of Cognitive and Neural Systems and Center for Adaptive Systems,
Boston University, MA 02215, USA.

The organization of neocortex into layers is one of its most salient anatomical
features. These layers include circuits that form functional columns in cortical
maps. A major unsolved problem concerns how bottom-up, top-down, and horizontal
interactions are organized within cortical layers to generate adaptive behaviors.
This article models how these interactions help visual cortex to realize: (i) the
binding process whereby cortex groups distributed data into coherent object
representations; (ii) the attentional process whereby cortex selectively
processes important events; and (iii) the developmental and learning processes
whereby cortex shapes its circuits to match environmental constraints. New
computational ideas about feedback systems suggest how neocortex develops and
learns in a stable way, and why top-down attention requires converging bottom-up
inputs to fully activate cortical cells, whereas perceptual groupings do not.

Publication Types: Research Support, U.S. Gov’t, Non-P.H.S. Review

PMID: 10221426 [PubMed – indexed for MEDLINE]

5: Conscious Cogn. 1999 Mar;8(1):1-44.

The link between brain learning, attention, and consciousness.

Grossberg S.

Department of Cognitive and Neural Systems, Boston University, MA 02215, USA.

The processes whereby our brains continue to learn about a changing world in a
stable fashion throughout life are proposed to lead to conscious experiences.
These processes include the learning of top-down expectations, the matching of
these expectations against bottom-up data, the focusing of attention upon the
expected clusters of information, and the development of resonant states between
bottom-up and top-down processes as they reach an attentive consensus between
what is expected and what is there in the outside world. It is suggested that all
conscious states in the brain are resonant states and that these resonant states
trigger learning of sensory and cognitive representations. The models which
summarize these concepts are therefore called Adaptive Resonance Theory, or ART,
models. Psychophysical and neurobiological data in support of ART are presented
from early vision, visual object recognition, auditory streaming, variable-rate
speech perception, somatosensory perception, and cognitive-emotional
interactions, among others. It is noted that ART mechanisms seem to be operative
at all levels of the visual system, and it is proposed how these mechanisms are
realized by known laminar circuits of visual cortex. It is predicted that the
same circuit realization of ART mechanisms will be found in the laminar circuits
of all sensory and cognitive neocortex. Concepts and data are summarized
concerning how some visual percepts may be visibly, or modally, perceived,
whereas amodal percepts may be consciously recognized even though they are
perceptually invisible. It is also suggested that sensory and cognitive
processing in the What processing stream of the brain obey top-down matching and
learning laws that are often complementary to those used for spatial and motor
processing in the brain’s Where processing stream. This enables our sensory and
cognitive representations to maintain their stability as we learn more about the
world, while allowing spatial and motor representations to forget learned maps
and gains that are no longer appropriate as our bodies develop and grow from
infanthood to adulthood. Procedural memories are proposed to be unconscious
because the inhibitory matching process that supports these spatial and motor
processes cannot lead to resonance. Copyright 1999 Academic Press.

Publication Types: Research Support, U.S. Gov’t, Non-P.H.S. Review

PMID: 10072692 [PubMed – indexed for MEDLINE]

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