Editing Binding problem (section)

=== Modern theories ===
Daniel Dennett<ref name="Dennett"/> has proposed that we, as humans, sensing our experiences as individual single events is illusory and that, instead, at any one time there are "multiple drafts" of sensory patterns at multiple sites. Each would only cover a fragment of what we think we experience. Arguably, Dennett is claiming that consciousness is not unified and there is no phenomenal binding problem. Most philosophers have difficulty with this position (see Bayne),<ref name="Bayne" /> but some physiologists agree with it. In particular, the demonstration of [[perceptual asynchrony]] in psychophysical experiments by Moutoussis and Zeki,<ref>{{Cite journal|last1=Moutoussis|first1=K.|last2=Zeki|first2=S.|date=1997-03-22|title=A direct demonstration of perceptual asynchrony in vision|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|volume=264|issue=1380|pages=393–399|doi=10.1098/rspb.1997.0056|pmc=1688275|pmid=9107055}}</ref><ref>{{Cite journal|last1=Moutoussis|first1=K.|last2=Zeki|first2=S.|date=1997-10-22|title=Functional segregation and temporal hierarchy of the visual perceptive systems|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|volume=264|issue=1387|pages=1407–1414|doi=10.1098/rspb.1997.0196|pmc=1688701|pmid=9364780}}</ref> where color is perceived before orientation of lines and before motion by 40 and 80 ms respectively, constitutes an argument that, over these very short time periods, different attributes are consciously perceived at different times, leading to the view that at least over these brief periods of time after visual stimulation, different events are not bound to each other, leading to the view of a disunity of consciousness,<ref>{{Cite journal|last=Zeki|first=S.|date=May 2003|title=The disunity of consciousness|journal=Trends in Cognitive Sciences|volume=7|issue=5|pages=214–218|doi=10.1016/s1364-6613(03)00081-0|pmid=12757823|s2cid=19365977|issn=1364-6613}}</ref> at least over these brief time intervals.  Dennett's view might be in keeping with evidence from recall experiments and change blindness purporting to show that our experiences are much less rich than we sense them to be – what has been called the Grand Illusion.<ref>{{cite journal|last1 = Blackmore|first1 = S. J.|last2 = Brelstaff|first2 = G.|last3 = Nelson|first3 = K.|last4 = Troscianko|first4 = T.|year = 1995|title = Is the richness of our visual world an illusion? Transsaccadic memory for complex scenes|journal = Perception|volume = 24|issue = 9|pages = 1075–81|doi = 10.1068/p241075|pmid = 8552459|s2cid = 28031132}}</ref> However, few, if any, other authors suggest the existence of multiple partial "drafts". Moreover, also on the basis of recall experiments, Lamme<ref name="Lamme">{{cite journal|last1 = Lamme|first1 = V|year = 2002|title = The grand Grand Illusion illusion|journal = Journal of Consciousness Studies|volume = 9|pages = 141–157}}</ref> has challenged the idea that richness is illusory, emphasizing that phenomenal content cannot be equated with content to which there is cognitive access.

Dennett does not tie drafts to biophysical events. Multiple sites of causal convergence are invoked in specific biophysical terms by Edwards<ref>{{cite journal|last1 = Edwards|first1 = J. C.|year = 2005|title = Is consciousness only a property of individual cells?|url = http://www.ucl.ac.uk/jonathan-edwards|journal = Journal of Consciousness Studies|volume = 12|pages = 60–76}}</ref> and Sevush.<ref>{{cite journal|last1 = Sevush|first1 = S|year = 2006|title = Single neuron theory of consciousness|journal = Journal of Theoretical Biology|volume = 238|issue = 3|pages = 704–725|doi = 10.1016/j.jtbi.2005.06.018|pmid = 16083912|bibcode = 2006JThBi.238..704S}}</ref> In this view the sensory signals to be combined in phenomenal experience are available, in full, at each of multiple sites. To avoid non-causal combination, each site/event is placed within an individual neuronal dendritic tree. The advantage is that "compresence" is invoked just where convergence occurs neuro-anatomically. The disadvantage, as for Dennett, is the counter-intuitive concept of multiple "copies" of experience. The precise nature of an experiential event or "occasion", even if local, also remains uncertain.

The majority of theoretical frameworks for the unified richness of phenomenal experience adhere to the intuitive idea that experience exists as a single copy, and draw on "functional" descriptions of distributed networks of cells. Baars<ref>Baars, B. J. (1997), In the Theater of Consciousness New York, Oxford University Press.</ref> has suggested that certain signals, encoding what we experience, enter a "Global Workspace" within which they are "broadcast" to many sites in the cortex for parallel processing. Dehaene, Changeux and colleagues<ref>{{cite journal|last1 = Dehaene|first1 = S.|last2 = Sergent|first2 = C.|last3 = Changeux|first3 = J.-P.|year = 2003|title = A neuronal network model linking subjective reports and objective physiological data during conscious perception|journal = Proceedings of the National Academy of Sciences|volume = 100|issue = 14|pages = 8520–8525|doi = 10.1073/pnas.1332574100|pmid = 12829797|pmc = 166261|bibcode = 2003PNAS..100.8520D|doi-access = free}}</ref> have developed a detailed neuro-anatomical version of such a workspace. Tononi and colleagues<ref>{{cite journal|last1 = Balduzzi|first1 = D|last2 = Tononi|first2 = G|year = 2008|title = Integrated information in discrete dynamical systems: motivation and theoretical framework|journal = PLOS Comput Biol|volume = 4|issue = 6|page = e1000091|doi = 10.1371/journal.pcbi.1000091|pmid = 18551165|pmc = 2386970|bibcode = 2008PLSCB...4E0091B|doi-access = free}}</ref> have suggested that the level of richness of an experience is determined by the narrowest information interface "bottleneck" in the largest sub-network or "complex" that acts as an integrated functional unit. Lamme<ref name="Lamme"/> has suggested that networks supporting reciprocal signaling rather than those merely involved in feed-forward signaling support experience. Edelman and colleagues have also emphasized the importance of re-entrant signaling<!--[16]-->.<ref>{{Cite journal|last=Edelman|first=Gerald M.|date=1993-02-01|title=Neural Darwinism: Selection and reentrant signaling in higher brain function|journal=Neuron|language=en|volume=10|issue=2|pages=115–125|doi=10.1016/0896-6273(93)90304-A|pmid=8094962|s2cid=8001773|issn=0896-6273}}</ref> Cleeremans<ref>{{cite journal|last1 = Cleeremans|first1 = A|year = 2011|title = The radical plasticity thesis|journal = Frontiers in Psychology|volume = 2|page = 86|doi = 10.3389/fpsyg.2011.00086|pmid = 21687455|pmc = 3110382|doi-access = free}}</ref> emphasizes meta-representation as the functional signature of signals contributing to consciousness.

In general, such network-based theories are not explicitly theories of how consciousness is unified, or "bound", but rather theories of functional domains within which signals contribute to unified conscious experience. A concern about functional domains is what Rosenberg<ref>Rosenberg, G. (2004) A Place for Consciousness. Oxford, Oxford University Press. {{ISBN|0-19-516814-3}}.</ref> has called the boundary problem; it is hard to find a unique account of what is to be included and what excluded. Nevertheless, this is, if anything is, the consensus approach.

Within the network context, a role for synchrony has been invoked as a solution to the phenomenal binding problem as well as the computational one. In his book, [[The Astonishing Hypothesis]],<ref>Crick, F. (1995) The Astonishing Hypothesis. Scribner Paperback {{ISBN|0-684-80158-2}} {{ISBN|978-0684801582}}</ref> Crick appears to be offering a solution to BP2 as much as BP1. Even von der Malsburg,<!--[19]--><ref>{{Cite journal|last1=von der Malsburg|first1=Ch.|last2=Schneider|first2=W.|date=1986-05-01|title=A neural cocktail-party processor|journal=Biological Cybernetics|language=en|volume=54|issue=1|pages=29–40|doi=10.1007/BF00337113|pmid=3719028|s2cid=25195155|issn=1432-0770}}</ref> introduces detailed computational arguments about object feature binding with remarks about a "psychological moment". The Singer group<!--[14]--><ref>{{Cite journal|last=Singer|first=Wolf|date=2006-01-25|title=Consciousness and the Binding Problem|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.2001.tb05712.x|journal=Annals of the New York Academy of Sciences|language=en|volume=929|issue=1|pages=123–146|doi=10.1111/j.1749-6632.2001.tb05712.x|pmid=11349422|s2cid=3174911|url-access=subscription}}</ref> also appear to be interested as much in the role of synchrony in phenomenal awareness as in computational segregation.

The apparent incompatibility of using synchrony to both segregate and unify might be explained by sequential roles. However, Merker<ref name="Merker 2013"/> points out what appears to be a contradiction in attempts to solve the subjective unity of perception in terms of a functional (effectively meaning computational) rather than a local biophysical domain in the context of synchrony.

Functional arguments for a role for synchrony are in fact underpinned by analysis of local biophysical events. However, Merker<ref name="Merker 2013"/> points out that the explanatory work is done by the downstream integration of synchronized signals in post-synaptic neurons: "It is, however, by no means clear what is to be understood by 'binding by synchrony' other than the threshold advantage conferred by synchrony at, and only at, sites of axonal convergence onto single dendritic trees..." In other words, although synchrony is proposed as a way of explaining binding on a distributed rather than a convergent basis, the justification rests on what happens at convergence. Signals for two features are proposed as bound by synchrony because synchrony effects downstream convergent interaction. Any theory of phenomenal binding based on this sort of computational function would seem to follow the same principle. The phenomenality would entail convergence, if the computational function does.

The assumption in many of the quoted models suggest that computational and phenomenal events, at least at some point in the sequence of events, parallel each other in some way. The difficulty remains in identifying what that way might be. Merker's<ref name="Merker 2013"/> analysis suggests that either (1) both computational and phenomenal aspects of binding are determined by convergence of signals on neuronal dendritic trees, or (2) that our intuitive ideas about the need for "binding" in a "holding together" sense in both computational and phenomenal contexts are misconceived. We may be looking for something extra that is not needed. Merker, for instance, argues that the homotopic connectivity of sensory pathways does the necessary work.