The cerebral cortex can be divided right down the middle
(sagittally) into two, nearly identical hemispheres. It has become clear to
neuroscientists in the last few decades why our brain has right and left
halves. Far from being redundant, they each process much of the same
information in slightly different ways, leading to two complementary and
cooperating worldviews. I will explain here why this organization (called
hemispheric lateralization) would be beneficial for AI.
Scientists that design AI systems are interested in how to
implement important features of the brain inside a computer. Neural networks
simulate many of these features today including neurons, axons, and their
hierarchical structure. However, neural networks are missing many of the human
brain’s key information processing principles. Hemispheric laterality may be
one such engineering principle that could give current AI systems the boost
they need to reach artificial general intelligence. The main benefit would be that over developmental time these two innately different networks would reprogram each other by being exposed to each other's outputs. In essence, two dissimilar heads are better than one.
Getting a neural network architecture (e.g. Reser, 2016) to
benefit from hemispheric laterality would actually be very easy. All you have
to do is duplicate the network you already have and then connect the two of
them via a large number of high bandwidth weighted links that would act as the
corpus callosum (the bundle of tracts that connect the right and left
hemispheres in mammals). The connections between them should respect the brain’s
natural bilateral symmetry, connecting similar and dissimilar areas across both
hemispheres. If you had a million dollar supercomputer running your AI system
and you wanted to create a whole other hemisphere, you would have to buy
another million dollars worth of hardware, but it may well be worth it. Next let's talk about how they would be different
Each hemisphere of the brain processes information slightly
differently. Despite the fact that the macrostructure of the two hemispheres is
almost identical, the two are different microstructurally. Many researchers believe
that this is because the right hemisphere has an average axonal length slightly
(microscopically) longer than the left. This means that the right brain has
relatively more white matter (axons), and the left hemisphere has relatively
more grey matter (cell bodies). This also means that on average the cells of
the right brain are further away from one another. There are many theories as
to why the longer-ranging wiring is responsible for the right hemisphere’s
tendency for broad generalization and holistic perspective. The left brain is
more densely woven and this might underlie its ability for detailed work and
close, quick cooperation between neurons.
People with a left hemisphere injury may have impaired
perception of high resolution, or detailed aspects of an image, whereas those
with right hemisphere injury may have trouble seeing the low resolution, or big
picture aspects of an image. In other words, they miss the forest for the
trees. Moreover, attending to the Ds in the figure below activates the left
hemisphere, whereas concentrating on the “L” that these Ds form activates the
right.
D
D
D
D
D D D
D D
It takes messages just a tiny bit longer to travel from one
neuron to another in the right hemisphere. Neuroscientists think that this
causes the two hemispheres to process the same informational inputs slightly
differently. Each side learns during its development while organizing its
thoughts according to a different algorithm and this leads each hemisphere to
become a master at its unique way of perceiving and responding to the world.
This discrepancy in temporal processing parameters makes the feedback and
crosstalk between these two non-identical specialists meaningful. These would be commensurate to specialists that could check, balance, reconcile, compare, and contrast their approaches. If they
processed information in exactly the same way it would be unnecessary to have
two, but because they don’t they provide a type of stereoscopic view on the
world similar to the view provided by our two offset eyes. This enables them to
form their own perceptions and opinions and then reconcile with one another. Right
now, no AI systems have anything like this.
It would be easy for the AI architect to take two identical
neural networks and then alter each one so that they are each capable of
generating different, but equally valid perspectives on reality. There are
countless parameters that could be fine-tuned to do this. However, they should
probably start with the average connectional distance between neural nodes in
the network. If the hardware was neuromorphic they could literally increase the
length of the axons, or if the software was responsible for rendering the
network then brief variable pauses could be introduced between the links. In a
computer these variables could be changed at any time according to processing
priorities. In other words, if the AI system anticipated that its left
hemisphere should “lean” even more to the left to help it solve a particular
problem, it could alter these “temporal weights” in real time. There would be
too much complexity in finding the optimal parameters to use human trial and
error, and instead genetic algorithms would have to be used.
Our brain’s two hemispheres also differ as to their value
systems. Our left hemisphere is dedicated to approach behaviors, and our right
hemisphere is dedicated to withdrawal behaviors. Stimulating the left
hemisphere of a rat will make it go toward a new object, whereas stimulating
the right side will make it back away from that object. The fact that
vertebrate brains have made this fundamental differentiation between approach
and withdrawal for hundreds of millions of years suggests that it might
represent an organizing principle that should be used in AI. One way to do this
would be to wire up the AI’s “subcortical” appetitive and motivational centers
(like the ventral tegmental area and the nucleus accumbens) involved in
reinforcement learning with the left hemisphere, and to wire up the threat
detection centers (like the amygdala) involved in punishment learning with the
right hemisphere. Can you think of a more important distinction between two
fundamentally important behavioral influencers? I can’t. AI needs two,
functionally equivalent, dedicated processors, one for
approach/liking/curiosity, and one for withdrawal/disliking/fear. As I have explained
elsewhere both hemispheres should influence the dopaminergic system and
sustained firing so that important rewards and threats can be maintained in
mind; however, the left should be focused on approaching those rewards, and the
right should be focused on withdrawing from the threats.
In the mammal brain, at any moment in time one hemisphere
will be more active than the other (dominant). Its behavior at that point in
time will be influenced by the dominant hemisphere. Approach and withdrawal
form a pivoting scale for how we act in the world. They also structure our
conscious attention even when we aren’t moving or behaving by allowing us to
pivot between interest and disinterest. The AI agent would also have to
continually select a dominant hemisphere to give priority to either approach or
withdrawal at every point in time.
As in vertebrate animals, the left hemisphere could be used
to control the right half of the AI’s robot body and the right hemisphere could
be used to control the left half. This could be a good way to ensure that both
approach and withdrawal have equal potential behavioral outputs. It seems that
this would create a robot whose two sides would pull it in different
directions. But this is how it works in the brain and you and I aren’t pulled
in two directions. The fact that both networks are so densely connected through
the corpus callosum, and that they developed together side by side probably
play a big role in their cooperativity.
Certainly, widespread hemispheric lateralization in
vertebrate animals indicates that laterality is associated with an evolutionary
advantage. It is pretty clear to see that its unique features could also
contribute to consciousness. This dichotomous organization might be similarly
advantageous in the creation of human-like intelligence, and superintelligence
in computers.
Physiology and Behavior. 167: 222-237.
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