Different brain areas process sight, sound and smell data that is somehow “bound” into one experience of thoughts, feelings and actions. Descartes explanation was that all sense data cleared through the pituitary gland to present to the conscious mind, like a little man in the brain watching a movie, but that little man would need another little man inside him to see his movie, and so on (Dennett, 1991) (Figure 6.34). The mind viewing a picture doesn’t make sense but physical realism isn’t much better as it concludes that each neuron in the brain:
“… doesn’t ‘know’ it is creating you in the process, but there you are, emerging from its frantic activity almost magically.” (Hofstadter & Dennett, 1981) p352.
That nerves with no ability to observe just act and “there you are” makes even less sense than dualism. The mind-body problem of centuries ago remains in neuroscience today as the mystery of how distant brain areas bind their activity to create a single observer/actor:
“One of the most famous continuing questions in computational neuroscience is called ‘The Binding Problem’. In its most general form, ‘The Binding Problem’ concerns how items that are encoded by distinct brain circuits can be combined for perception, decision, and action.” (Feldman, 2013) p1.
The binding problem arises because distant processing hierarchies can’t just exchange data. They can’t “talk” as global workspace theory says they do (6.1.6) because when a visual cortex nerve fires to register a line, it doesn’t say “I saw a line” like a little person. It just fires a yes-no response like any other neuron. To bind that response to another feature like redness needs higher processing in the same hierarchy. At each step in a processing hierarchy, a nerve can fire to trigger a motor response but it isn’t an integrated experience because the nerve doesn’t know why it fired. The six-layered visual cortex can process lines, shapes, colors and textures but the last nerve to fire in a sequence knows no more than the first. To integrate vision and smell needs a higher area to process both outputs, but brain studies show this doesn’t happen.
Different areas evolved to process sight, smell, sound, thoughts, feelings, touch and memory but no area evolved to integrate them all. If it had, the brain would be wired like a computer motherboard with many lines to a central processor, but it isn’t. Each brain area is encapsulated, so smell, sight and sound brain areas can’t exchange any experiences they have with each other:
“Because of the principle of encapsulation, conscious contents cannot influence each other either at the same time nor across time, which counters the everyday notion that one conscious thought can lead to another conscious thought … content generators cannot communicate the content they generate to another content generator. For example, the generator charged with generating the color orange cannot communicate ‘orange’ to any other content generator because only this generator (a perceptual module) can, in a sense, understand and instantiate ‘orange’.” (Morsella et al., 2016) p12
Even if there was higher processing to integrate all brain areas, it would be too slow, just as complex thought usually manages to come up with a witty retort after a conversation is over. Our brain can integrate perceptions with memory to drive motor acts in less than a second but if one hierarchy did this, it would be too slow. The binding problem is that the brain is integrated in a way that its wiring doesn’t support, so the unified experience of senses, feelings, thoughts and actions we have should be impossible.
Encapsulation predicts that cortical hemispheres can’t exchange data, so each only ever sees half the visual field, so cutting the nerves between the hemispheres doesn’t give a sense of loss:
“… despite the dramatic effects of callosotomy, W.J. and other patients never reported feeling anything less than whole. As Gazzaniga wrote many times: the hemispheres didn’t miss each other.” (Wolman, 2012)
Why don’t split-brain patients know the corpus callosum is cut? If the optic nerve is cut, we know we are blind as no data comes from the eyes. If an injury cuts the spinal cord, we know we are paralyzed as no data comes from the legs. But when the millions of nerves connecting the hemispheres are cut, both carry on as before! Why doesn’t the verbal hemisphere report a loss of data? If it normally sees the entire field thanks to the other hemisphere, it should report being half blind, but it doesn’t. It follows that it doesn’t report any missing data because there is none.
Instead of data loss, cutting the corpus callosum divides consciousness. One patient couldn’t smoke because when the right hand put a lit cigarette in his mouth, the left hand removed it, and another found her left hand slapping her awake if she overslept (Dimond, 1980) p434. Conflicts made simple tasks take longer – one patient found his left hand unbuttoning a shirt as the right tried to button it. Another found that when shopping, one hand put back on the shelf items the other had put in the basket. One patient struggled to walk home as one half of his body tried to visit his ex-wife while the other tried to walk home. These extraordinary but well documented cases show that cutting the corpus callosum gives two hemispheres with different experiences and opinions about what the body should do.