From: Rafal Smigrodzki (rafal@smigrodzki.org)
Date: Fri Feb 14 2003 - 23:21:38 MST
From: <brent.allsop@attbi.com>
To: <extropians@extropy.org>
Sent: Friday, February 14, 2003 4:01 PM
Subject: RE: Where the I is
>
> Rafal Smigrodzki <rafal@smigrodzki.org> commented:
>
> >>>However, we have to remember that only a very small number of neurons, if
> any, in the primary visual cortex, is correlated with conscious experience.<<<
>
> This can only be true if you are talking about the voluntary cognitive part of
> conscious experience. Though important, this voluntary part is a small part of
> conscious experience. Everything we experience visually fills the primary
> visual cortex. This is the non-voluntary part of conscious experience. The
> non-voluntary nature leads to the deception that it is really what we are
> looking at beyond our senses, rather than simply our involuntary representation
> in the visual cortex. If there is any damage any place in the primary visual
> cortex the corresponding involuntary space in our visual awareness no longer
> exists. The primary visual cortex is a very big part of conscious experience.
>
### I do not quite understand your above paragraph. Specifically, I do not know what is "voluntary cognitive part of conscious experience".
In any case, my comment you quoted refers to the progressive increase in the percentage of neurons whose activity correlates with conscious experience as one goes from V1 to the parietal to frontal cortices. Please see the abstracts below.
Rafal
Neuron 2002 Dec 5;36(5):791-804
View from the top: hierarchies and reverse hierarchies in the visual system.
Hochstein S, Ahissar M.
Department of Neurobiology, Neural Computation Center, Hebrew University, Jerusalem, Israel. shaul@vms.huji.ac.il
We propose that explicit vision advances in reverse hierarchical direction, as shown for perceptual learning. Processing along the feedforward hierarchy of areas, leading to increasingly complex representations, is automatic and implicit, while conscious perception begins at the hierarchy's top, gradually returning downward as needed. Thus, our initial conscious percept--vision at a glance--matches a high-level, generalized, categorical scene interpretation, identifying "forest before trees." For later vision with scrutiny, reverse hierarchy routines focus attention to specific, active, low-level units, incorporating into conscious perception detailed information available there. Reverse Hierarchy Theory dissociates between early explicit perception and implicit low-level vision, explaining a variety of phenomena. Feature search "pop-out" is attributed to high areas, where large receptive fields underlie spread attention detecting categorical differences. Search for conjunctions or fine discriminations depends on reentry to low-level specific receptive fields using serial focused attention, consistent with recently reported primary visual cortex effects.
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Vision Res 2000;40(10-12):1507-21
The role of primary visual cortex (V1) in visual awareness.
Lamme VA, Super H, Landman R, Roelfsema PR, Spekreijse H.
Department of Visual System Analysis, AMC, Graduate School of Neurosciences, University of Amsterdam, P.O. Box 12011, 1100 AA, Amsterdam, The Netherlands. v.lamme@amc.uva.nl
In the search for the neural correlate of visual awareness, much controversy exists about the role of primary visual cortex. Here, the neurophysiological data from V1 recordings in awake monkeys are examined in light of two general classes of models of visual awareness. In the first model type, visual awareness is seen as being mediated either by a particular set of areas or pathways, or alternatively by a specific set of neurons. In these models, the role of V1 seems rather limited, as the mere activity of V1 cells seems insufficient to mediate awareness. In the second model type, awareness is hypothesized to be mediated by a global mechanism, i.e. a specific kind of activity not linked to a particular area or cell type. Two separate versions of global models are discussed, synchronous oscillations and spike rate modulations. It is shown that V1 synchrony does not reflect perception but rather the horizontal connections between neurons, indicating that V1 synchrony cannot be a direct neural correlate of conscious percepts. However, the rate of spike discharges of V1 neurons is strongly modulated by perceptual context, and these modulations correlate very well with aspects of perceptual organization, visual awareness, and attention. If these modulations serve as a neural correlate of visual awareness, then V1 contributes to that neural correlate. Whether V1 plays a role in the neural correlate of visual awareness thus strongly depends on the way visual awareness is hypothesized to be implemented in the brain.
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Neuroimage 2001 Apr;13(4):654-61
Is V1 necessary for conscious vision in areas of relative cortical blindness?
Kleiser R, Wittsack J, Niedeggen M, Goebel R, Stoerig P.
Institute of Experimental Psychology, Heinrich-Heine-University, Dusseldorf, 40225, Germany.
Visual field defects result from postgeniculate lesions. It is generally assumed that absolute defects are caused by total destruction or denervation of primary visual cortex (V1) and that the degraded but conscious vision that remains or returns in relative or partial defects is mediated by compromised V1 cortex that retains a sufficiently large population of functional neurons. We here report the results of three patients with long-standing postgeniculate lesions who underwent functional magnetic resonance imaging while their partial defect was stimulated with high-contrast reversing checkerboard stimuli. Although the stimulation evoked conscious visual impressions in all three, in only one patient did it activate perilesional V1. In the other two we found no evidence for perilesional activation, indicating that some conscious vision may return in the absence of functional ipsilesional V1. Copyright 2001 Academic Press.
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