[4] A popular hypothesis mentioned by neuroscientist Prof 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.
[5][6] 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.
[7] 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.
[8] 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.
[9] 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.
This rhythmic firing appears to be linked to intrinsic oscillations in neuronal somatic potentials, typically in the gamma range around 40 – 60 hertz.
[10] The positive arguments for a role for rhythmic synchrony in resolving the segregational object-feature binding problem have been summarized by Neurophysiologist Prof Singer.
Shadlen and Movshon[6] raise a series of doubts about both the theoretical and the empirical basis for the idea of segregational binding by temporal synchrony.
At best synchrony can facilitate segregation supported by other means (as physicist and neuroscientist Prof von der Malsburg acknowledges).
[17] 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,[18] 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.
However, both Marr[23] and Barlow[24] 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.
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.
Local field potentials were recorded from the lateral prefrontal cortex (lPFC) in monkeys and were monitored during different stimulus configurations.
[27] Smythies[28] defines the combination problem, also known as the subjective unity of perception, as "How do the brain mechanisms actually construct the phenomenal object?".
There is a wide range of views on just how real this "unity" is, but the existence of medical conditions in which it appears to be subjectively impaired, or at least restricted, suggests that it is not entirely illusory.
Different visual features such as color, size, shape, and motion are computed by largely distinct neural circuits but we experience this as an integrated whole.
[38] Early philosophers René Descartes and Gottfried Wilhelm Leibniz[39] noted that the apparent unity of our experience is an all-or-none qualitative characteristic that does not appear to have an equivalent in the known quantitative features, like proximity or cohesion, of composite matter.
William James,[40] in the nineteenth century, considered the ways the unity of consciousness might be explained by known physics and found no satisfactory answer.
Whitehead[41] proposed a fundamental ontological basis for a relation consistent with James's idea of co-consciousness, in which many causal elements are co-available or "compresent" in a single event or "occasion" that constitutes a unified experience.
Descartes's central "soul" is now rejected because neural activity closely correlated with conscious perception is widely distributed throughout the cortex.
[44] Experiments have shown that ferritin and neuromelanin in fixed human substantia nigra pars compacta (SNc) tissue are able to support widespread electron tunneling.
[45] Further experiments have shown that ferritin structures similar to ones found in SNc tissue are able to conduct electrons over distances as great as 80 microns, and that they behave in accordance with Coulomb blockade theory to perform a switching or routing function.
Baars[57] 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.
Tononi and colleagues[59] 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.
A concern about functional domains is what Rosenberg[62] has called the boundary problem; it is hard to find a unique account of what is to be included and what excluded.
Even von der Malsburg,[64] introduces detailed computational arguments about object feature binding with remarks about a "psychological moment".
However, Merker[21] 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.
In modern connectionism, cognitive neuroarchitectures are developed (e.g. "Oscillatory Networks",[66] "Integrated Connectionist/Symbolic (ICS) Cognitive Architecture",[67] "Holographic Reduced Representations (HRRs)",[68] "Neural Engineering Framework (NEF)"[69]) that solve the binding problem by means of integrative synchronization mechanisms (e.g. the (phase-)synchronized "Binding-by-synchrony (BBS)" mechanism) According to bioengineering Prof Igor Val Danilov,[74] the Mother-fetus Neurocognitive model[75] - knowledge about neurophysiological processes during Shared intentionality - can reveal insights into the binding problem and even the perception of object development since intentionality succeeds before organisms confront the binding problem.
The application of embodied information requires an already categorised environment onto objects — holistic representation of reality — which occurs through (and only after the emergence of) perception and intentionality.
[76][77] In short, properties of the mother's heart – the electromagnetic and acoustic oscillations – converge the neuronal activity of both nervous systems in an ensemble, shaping synchrony.