What is the binding problem in consciousness?

The binding problem concerns how items encoded by distinct brain circuits are combined for perception, decision and action. In consciousness research it takes a sharper form: different features of a scene, such as color, shape and motion, are handled by largely separate neural circuits, yet we experience one integrated whole. How that unity arises is still unexplained. [1]

A canonical example, traced to Rosenblatt in 1961, is the need to associate one visual feature, such as an object's shape, with another, such as its location, to form a unified representation of the object. This matters most when several objects are present, because features from different objects could otherwise be combined wrongly. Such errors are called illusory conjunctions, and psychological evidence shows they do occur, which suggests binding is a real task for the brain. [2]

Another description uses a garden scene. Nothing in the light reaching the retina distinguishes the bark of a tree from the surrounding shrubs, yet we experience the tree as a single whole. The same question applies across senses, for instance when the sight of a tree and the rustle of its leaves are experienced together even though they involve visual and auditory cortex. [3]

A review in the NIH's PMC archive argues that the neural binding problem comprises at least four distinct problems: general coordination, visual feature-binding, variable binding, and the subjective unity of perception. It says confusion arises because these are lumped together, and that scientific understanding differs greatly among them. Progress is being made on coordination across brain areas, while the subjective unity of perception remains mysterious. [1]

Revonsuo makes a similar point. He writes that it is not clear what the binding problem is supposed to be or how it relates to consciousness. Some formulations never mention consciousness, while others tie directly to phenomenal experience and to the classical philosophical problem of the unity of consciousness. In his view only part of the empirical binding research bears on consciousness, and the science of consciousness needs a clearer theory of how the two relate. [4]

The PMC review treats the subjective unity of perception as an instance of the mind-body problem, the relation between subjective experience and neural function. It notes that the brain contains no stable, high-resolution, full-field representation of a visual scene, even though that is what we seem to experience. Vision is detailed only over about one degree at the fovea, and we make about three saccades per second. The primate visual system has been mapped in detail and contains no area that could hold such a representation, so the experience does not match the neural circuitry. [1]

The review offers a plausible functional account of the stable-world illusion, based on memory, other senses and the periphery's sensitivity to change, but says this does not explain the neural mechanisms. A Neuron editorial put the broader question this way: whether the mechanisms that attribute the correct color and shape to an object are the same ones that produce unified phenomenal experience, and whether solving binding would solve consciousness. It posed these as open questions. [1] [2]

Some work speculates that temporal synchrony, the coordinated timing of neural firing, plays a role in the subjective unity of perception. The PMC review describes this as speculative and says that general coordination across areas must be part of the substrate of experience, without claiming the problem is solved. [1]