Binding problem

The binding problem is "the problem of how the unity of conscious perception is brought about by the distributed activities of the central nervous system."

It arises whenever information from distinct populations of neurons must be combined. The activity of specialised sets of neurons dealing with different aspects of perception are combined to form a unified perceptual experience. The binding problem also occurs in each modality of perception and different versions of the problem have been described in language production, visual perception, auditory perception, and other mental processes.

In the case of visual perception, the brains of humans and other animals process different aspects of perception by separating information about those aspects and processing them in distinct regions of the brain. For example, different areas in the visual cortex specialise in processing the different aspects of colour, motion, and shape. This type of modular coding yields ambiguity in many instances. For example, when humans view a scene containing a red circle and a green square, some neurons signal the presence of red, others signal the presence of green, still others the circle shape and square shape. Here, the binding problem is the issue of how the brain represents the pairing of color and shape. Specifically, are the circles red or green?

The binding problem is also an issue in memory. How do we remember the associations among different elements of an event? How does the brain create and maintain those associations? Both the hippocampus and prefrontal cortex seem to be important for memory binding.

The binding problem is also closely related to the problem of the homunculus needed to explain who is watching the wonderfully integrated internal TV screen. The alternative to a ghost in the machine in this context is infinite regress. But of course regardless of which objective correlates relate to some process involved in the binding, the problem of how the subjective awareness of the internal 'virtual reality' screen arises is not solved. This is the hard problem of consciousness, with its implication of a homunculus.

A popular hypothesis is that features are bound via synchronisation of the firing of different neurons in the cortex. Andreas K. Engel and his coworkers (1992) have found that two different neurons with a different receptive field produce divergent correlograms according to whether the stimuli were bound together or not. However, Thiele and Stoner (2003) found that perceptual binding of two moving patterns had no effect on synchronization of the neurons responding to the two patterns.