Types of Binding

Excerpt from “Mindmelding: Consciousness, Neuroscience, and the Mind’s Privacy” (2012) by William Hirstein (pgs. 57-58 and 64-65)

The Neuroscience of Binding

When you experience an orchestra playing, you see them and hear them at the same time. The sights and sounds are co-conscious (Hurley, 2003; de Vignemont, 2004). The brain has an amazing ability to make everything in consciousness co-conscious with everything else, so that the co-conscious relation is transitive: That means, if x is co-conscious with y, and y is co-conscious with z, then x is co-conscious with z. Brain researchers hypothesized that the brain’s method of achieving co-consciousness is to link the different areas embodying each portion of the brain state by a synchronizing electrical pulse. In 1993, Linás and Ribary proposed that these temporal binding processes are responsible for unifying information from the different sensory modalities. Electrical activity, “manifested as variations in the minute voltage across the cell’s enveloping membrane,” is able to spread, like “ripples in calm water” according to Linás (2002, pp.9-10). This sort of binding has been found not only in the visual system, but also in other modalities (Engel et al., 2003). Bachmann makes the important point that the binding processes need to be “general and lacking any sensory specificity. This may be understood via a comparison: A mirror that is expected to reflect equally well everything” (2006, 32).

Roelfsema et al. (1997) implanted electrodes in the brain of cats and found binding across parietal and motor areas. Desmedt and Tomberg (1994) found binding between a parietal area and a prefrontal area nine centimeters apart in their subjects, who had to respond with one hand, to signal which finger on another hand had been stimulated – a conscious response to a conscious perception. Binding can occur across great distances in the brain. Engel et al. (1991) also found binding across the two hemispheres. Apparently binding processes can produce unified conscious states out of cortical areas widely separated. Notice, however, that even if there is a single area in the brain where all the sensory modalities, memory, and emotion, and anything else that can be in a conscious state were known to feed into, binding would still be needed. As long as there is any spatial extent at all to the merging area, binding is needed. In addition to its ability to unify spatially separate areas, binding has a temporal dimension. When we engage in certain behaviors, binding unifies different areas that are cooperating to produce a perception-action cycle. When laboratory animals were trained to perform sensory-motor tasks, the synchronized oscillations were seen to increase both within the areas involved in performing the task and across those areas, according to Singer (1997).

Several different levels of binding are needed to produce a full conscious mental state:

  1. Binding of information from many sensory neurons into object features
  2. Binding of features into unimodal representations of objects
  3. Binding of different modalities, e.g., the sound and movement made by a single object
  4. Binding of multimodal object representations into a full surrounding environment
  5. Binding of representations, emotions, and memories, into full conscious states.

So is there one basic type of binding, or many? The issue is still debated. On the side of there being a single basic process, Koch says that he is content to make “the tentative assumption that all the different aspects of consciousness (smell, pain, vision, self-consciousness, the feeling of willing an action, of being angry and so on) employ one or perhaps a few common mechanisms” (2004, p15). On the other hand, O’Reilly et al. argue that “instead of one simple and generic solution to the binding problem, the brain has developed a number of specialized mechanisms that build on the strengths of existing neural hardware in different brain areas” (2003, p.168).


What is the function of binding?

We saw just above that Crick and Koch suggest a function for binding, to assist a coalition of neurons in getting the “attention” of prefrontal executive processes when there are other competitors for this attention. Crick and Koch also claim that only bound states can enter short-term memory and be available for consciousness (Crick and Koch, 1990). Engel et al. mention a possible function of binding: “In sensory systems, temporal binding may serve for perceptual grouping and, thus, constitute an important prerequisite for scene segmentation and object recognition” (2003, 140). One effect of malfunctions in the binding process may be a perceptual disorder in which the parts of objects cannot be integrated into a perception of the whole object. Riddoch and Humphreys (2003) describe a disorder called ‘integrative agnosia’ in which the patient cannot integrate the parts of an object into a whole. They mention a patient who is given a photograph of a paintbrush but sees the handle and the bristles as two separate objects. Breitmeyer and Stoerig (2006, p.43) say that:

[P]atients can have what are called “apperceptive agnosia,” resulting from damage to object-specific extrastriate cortical areas such as the fusiform face area and the parahippocampal place area. While these patients are aware of qualia, they are unable to segment the primitive unity into foreground or background or to fuse its spatially distributed elements into coherent shapes and objects.

A second possible function of binding is a kind of bridging function, it makes high-level perception-action cycles go through. Engel et al. say that, “temporal binding may be involved in sensorimotor integration, that is, in establishing selective links between sensory and motor aspects of behavior” (2003, p.140).

Here is another hypothesis we might call the scale model theory of binding. For example, in order to test a new airplane design in a wind tunnel, one needs a complete model of it. The reason for this is that a change in one area, say the wing, will alter the aerodynamics of the entire plane, especially those areas behind the wing. The world itself is quite holistic. […] Binding allows the executive processes to operate on a large, holistic model of the world in a way that allows the model to simulate the same holistic effects found in the world. The holism of the represented realm is mirrored by a type of brain holism in the form of binding.

See also these articles about (phenomenal) binding:

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