The unity of consciousness and (cognitive) binding problem is the problem of how objects, background, and abstract or emotional features are combined into a single experience. The binding problem refers to the overall encoding of our brain circuits for the combination of decisions, actions, and perception. It is considered a "problem" because no complete model exists.
The binding problem can be subdivided into the four areas of perception, neuroscience, cognitive science, and the philosophy of mind. It includes general considerations on coordination, the subjective unity of perception, and variable binding.
General considerations on coordination Summary of problem Attention is crucial in determining which phenomena appear to be bound together, noticed, and remembered. This specific binding problem is generally referred to as temporal synchrony. At the most basic level, all neural firing and its adaptation depends on specific consideration to timing (Feldman, 2010). At a much larger level, frequent patterns in large scale neural activity are a major diagnostic and scientific tool.The Neural Binding Problem(s) Jerome Feldman ... – Icsi.berkeley.edu. https://www.icsi.berkeley.edu/pubs/ai/ICSI_NBPs12.pdf.
Synchronization theory and research A popular hypothesis mentioned by neuroscientist Peter Milner, in his 1974 article A Model for Visual Shape Recognition, has been that features of individual objects are bound/segregated via synchronization of the activity of different neurons in the cortex.Shadlen MN, Movshon JA (September 1999). "Synchrony unbound: a critical evaluation of the temporal binding hypothesis". Neuron. 24 (1): 67–77, 111–25. doi:10.1016/S0896-6273(00)80822-3. PMID 10677027. The theory, called binding-by-synchrony (BBS), is hypothesized to occur through the transient mutual synchronization of neurons located in different regions of the brain when the stimulus is presented. Empirical testing of the idea was brought to light when von der Malsburg proposed that feature binding posed a special problem that could not be covered simply by cellular firing rates.von der Malsburg, C. (1981). "The Correlation Theory of Brain Function". MPI Biophysical Chemistry, Internal Report 81–2. Reprinted in Models of Neural Networks II (1994), E. Domany, J.L. van Hemmen, and K. Schulten, eds. (Berlin: Springer). However, it has been shown this theory may not be a problem since it was revealed that the modules code jointly for multiple features, countering the feature-binding issue. Temporal synchrony has been shown to be the most prevalent when regarding the first problem, "General Considerations on Coordination," because it is an effective method to take in surroundings and is good for grouping and segmentation. A number of studies suggested that there is indeed a relationship between rhythmic synchronous firing and feature binding. This rhythmic firing appears to be linked to intrinsic oscillations in neuronal somatic potentials, typically in the gamma range around 40 – 60 hertz. The positive arguments for a role for rhythmic synchrony in resolving the segregational object-feature binding problem have been summarized by Neurophysiologist Wolf Singer. There is certainly extensive evidence for synchronization of neural firing as part of responses to visual stimuli.
However, there is inconsistency between findings from different laboratories. Moreover, a number of recent reviewers, including neuroscientists Michael Shadlen and J. Anthony Movshon and Bjorn Merker have raised concerns about the theory being potentially untenable. Neuroscientists Alexander Thiele and Gene Stoner found that perceptual binding of two moving patterns had no effect on synchronization of the neurons responding to two patterns: coherent and noncoherent plaids.Thiele A, Stoner G (2003). "Neuronal synchrony does not correlate with motion coherence in cortical area MT". Nature, 421, 366–370. In the primary visual cortex, Dong et al. found that whether two neurons were responding to contours of the same shape or different shapes had no effect on neural synchrony since synchrony is independent of binding condition.
Shadlen and Movshon raise a series of doubts about both the theoretical and the empirical basis for the idea of segregational binding by temporal synchrony. There is no biophysical evidence that cortical neurons are selective to synchronous input at this point of precision, and cortical activity with synchrony this precise is rare. Synchronization is also connected to endorphin activity. It has been shown that precise spike timing may not be necessary to illustrate a mechanism for visual binding and is only prevalent in modeling certain neuronal interactions. In contrast, Anil Seth describes an artificial brain-based robot that demonstrates multiple, separate, widely distributed neural circuits, firing at different phases, showing that regular brain oscillations at specific frequencies are essential to the neural mechanisms of binding.
Cognitive psychologists Liat Goldfarb and Anne Treisman point out that a logical problem appears to arise for binding solely via synchrony if there are several objects that share some of their features and not others.Goldfarb, L.; Treisman, A. (Mar 2013). "Counting multidimensional objects: implications for the neural-synchrony theory". Psychological Science. 24 (3): 266–71. doi:10.1177/0956797612459761. PMID 23334446. S2CID 13448695. At best synchrony can facilitate segregation supported by other means (as physicist and neuroscientist Christoph von der Malsburg acknowledges).von der Malsburg, C. (Sep 1999). "The what and why of binding: the modeler's perspective" (PDF). Neuron. 24 (1): 95–104, 111–25. doi:10.1016/s0896-6273(00)80825-9. PMID 10677030
A number of neuropsychological studies suggest that the association of color, shape and movement as "features of an object" is not simply a matter of linking or "binding", but shown to be inefficient to not bind elements into groups when considering association,von der Malsburg, Christoph. "The What and Why of Binding: The Modeler's Perspective." Cogprints, 1 September 1999, https://web-archive.southampton.ac.uk/cogprints.org/1488/. and give extensive evidence for top-down feedback signals that ensure that sensory data are handled as features of (sometimes wrongly) postulated objects early in processing. Pylyshyn has also emphasized the way the brain seems to pre-conceive objects from which features are to be allocated to which are attributed continuing existence even if features such as color change. This is because visual integration increases over time, and indexing visual objects helps to ground visual concepts.
Feature integration theory Summary of problem The visual feature binding problem refers to the question of why we do not confuse a red circle and a blue square with a blue circle and a red square. The understanding of the circuits in the brain stimulated for visual feature binding is increasing. A binding process is required for us to accurately encode various visual features in separate cortical areas.
In her feature integration theory, Treisman suggested that one of the first stages of binding between features is mediated by the features' links to a common location. The second stage is combining individual features of an object that requires attention, and selecting that object occurs within a "master map" of locations. Psychophysical demonstrations of binding failures under conditions of full attention provide support for the idea that binding is accomplished through common location tags.
An implication of these approaches is that sensory data such as color or motion may not normally exist in "unallocated" form. For Merker: "The 'red' of a red ball does not float disembodied in an abstract color space in V4." If color information allocated to a point in the visual field is converted directly, via the instantiation of some form of propositional logic (analogous to that used in computer design) into color information allocated to an "object identity" postulated by a top-down signal as suggested by Purves and Lotto (e.g. There is blue here + Object 1 is here = Object 1 is blue) no special computational task of "binding together" by means such as synchrony may exist. (Although Von der Malsburg poses the problem in terms of binding "propositions" such as "triangle" and "top", these, in isolation, are not propositional.)
How signals in the brain come to have propositional content, or meaning, is a much larger issue. However, both MarrMarr, D. C. (1982) Vision. New York, Freeman. and Barlow suggested, on the basis of what was known about neural connectivity in the 1970s that the final integration of features into a percept would be expected to resemble the way words operate in sentences.
The role of synchrony in segregational binding remains controversial. Merker has recently suggested that synchrony may be a feature of areas of activation in the brain that relates to an "infrastructural" feature of the computational system analogous to increased oxygen demand indicated via BOLD signal contrast imaging. Apparent specific correlations with segregational tasks may be explainable on the basis of interconnectivity of the areas involved. As a possible manifestation of a need to balance excitation and inhibition over time it might be expected to be associated with reciprocal re-entrant circuits as in the model of Anil Seth. (Merker gives the analogy of the whistle from an audio amplifier receiving its own output.)
Experimental work Visual feature binding is suggested to have a selective attention to the locations of the objects. If indeed spatial attention does play a role in binding integration it will do so primarily when object location acts as a binding cue. A study's findings have shown that functional MRI images indicate regions of the parietal cortex involved in spatial attention, engaged in feature conjunction tasks in single feature tasks. The task involved multiple objects being shown simultaneously at different locations which activated the parietal cortex, whereas when multiple objects are shown sequentially at the same location the parietal cortex was less engaged.
Behavioral experiments Dezfouli et al. investigated feature binding through two feature dimensions to disambiguate whether a specific combination of color and motion direction is perceived as bound or unbound. Two behaviorally relevant features, including color and motion belonging to the same object, are defined as the "bound" condition, whereas the "unbound" condition has features that belong to different objects. Local field potentials were recorded from the lateral prefrontal cortex (lPFC) in monkeys and were monitored during different stimulus configurations. The findings suggest a neural representation of visual feature binding in 4 to 12 Hertz frequency bands. It is also suggested that transmission of binding information is relayed through different lPFC neural subpopulations. The data shows behavioral relevance of binding information that is linked to the animal's reaction time. This includes the involvement of the prefrontal cortex targeted by the dorsal and ventral visual streams in binding visual features from different dimensions (color and motion).
It is suggested that the visual feature binding consists of two different mechanisms in visual perception. One mechanism consists of agonistic familiarity of possible combinations of features integrating several temporal integration windows. It is speculated that this process is mediated by neural synchronization processes and temporal synchronization in the visual cortex. The second mechanism is mediated by familiarity with the stimulus and is provided by attentional top-down support from familiar objects.
Consciousness and binding Summary of problem