
Are our brains Bayesian? (2016) - sajid
https://rss.onlinelibrary.wiley.com/doi/full/10.1111/j.1740-9713.2016.00935.x
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jedberg
I've been studying how the brain works since college, which is now 20+ years.
One thing a professor said back then really sticks out -- "we always assume
that the brain works the same way as the most advanced computing of the time".
In the 50s we assumed the brain worked like a telephone switching system. In
the 80s we assumed the brain worked like a bunch of transistors.

In the 90s we finally switched it up, and developed computing paradigms based
on human biology, and came up with applying neural nets to brain science. Then
someone had the idea to create a Bayesian NN.

Each iteration we get closer to explaining how the brain works, but showing
that each iteration is closer to workable based on our knowledge of the
biology of the brain.

But we still have no idea how we get from brain biology to rational (and
irrational) thought. I'd be excited if we solved this within my lifetime.

~~~
TaupeRanger
I don't think it will be, unfortunately. I think it's important to distinguish
between explaining "how the brain works" and "understanding the brain, the
mind, and their relationship". There are hundreds of studies every year
elucidating correlations between certain kinds of brain activity and certain
states of conscious experience. There are also many valiant attempts at
modeling various aspects of human cognition and brain function. Unfortunately,
none of this research says anything at all about the nature of the actual
feelings and experiences we have.

People are taught in school that a sufficient response to the question "how do
we hear things?" is to talk about sound waves, the shape of the outer ear, the
tympanic membrane, malleus, incus, stapes, cochlea, etc. At some point you
arrive at: "and then the brain processes the signal in the auditory cortex and
stuff." We have become accustomed to this sort of answer, but it really
doesn't even begin to answer the real (and interesting) question: why does all
that processing result in the felt experience of hearing, rather than the
nervous system just bubbling up and causing a behavior with no feelings? Why
does it "feel" that way and not some other way? Is there a different kind of
hearing that "feels" fundamentally different from our experience?

My point is that, we are closer to explaining some functional aspects of the
brain, but when it comes to explaining the nature and character of our
qualitative experience, we are at the same place as the ancient Eastern
philosophers - we've really gotten nowhere.

~~~
red75prime
> why does all that processing result in the felt experience of hearing

Fortunately, it is a question, which can stay unanswered with no practical
consequences. It is a subjective counterpart of "Why is there something rather
than nothing?", and we aren't answering either anytime soon.

> Is there a different kind of hearing that "feels" fundamentally different
> from our experience?

Even if there is, we will need different brain hardware to experience it
first-hand, otherwise we'd have to do with analogies or, for more precision,
with functional descriptions of perceptual processing.

~~~
TaupeRanger
_Fortunately, it is a question, which can stay unanswered with no practical
consequences. It is a subjective counterpart of "Why is there something rather
than nothing?", and we aren't answering either anytime soon._

Utterly absurd and completely false. An explanation for the question of why
pain feels the why it does, for example, has enormous practical implications
and consequences. The current neurological and medical approaches to pain
management are poorly understood and often dangerous in extreme cases. We
literally don't know why or how Tylenol works. That is a huge problem. The
current best-case scenario, absent an explanation of the nature of the
character of pain experiences, is that we find some neural activities that we
can alter with advanced medical techniques which reliably suppress pain
experiences. But it's not clear that 1) we will ever find such techniques, 2)
that such techniques would exhaustively alter all the kinds of physical pain a
human might experience, 3) that such techniques wouldn't negatively alter
other aspects of a person's mind. If we had a fuller explanation of the nature
of the character of the experience itself (rather than just treating
consciousness like a black box), we might be able to alter the experiences
more precisely and appropriately.

~~~
red75prime
For all those ends you'll need observables: patient reports, behaviors
associated with pain and so on. You probably have in mind the question "why
this pain processing results in the observed effects?"

I was talking about the question "why does all that processing result in the
felt experience [...]?"

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TaupeRanger
No, I have in mind the exact question I outlined at the beginning of my
response.

~~~
red75prime
Then I don't understand you. What is important to address the problems you
outlined is the question of "How brain activity corresponds to the felt
experiences (as reported by subjects)?", not "Why there are felt experiences
corresponding to brain activity?"

Even if we had the answer for the second question (say, "There is immaterial
soul which is responsible for our felt experiences and that's why we feel"),
it will not help with pain treatment.

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mlechha
Whenever this comes up, I think about the conjunction fallacy
[https://en.m.wikipedia.org/wiki/Conjunction_fallacy](https://en.m.wikipedia.org/wiki/Conjunction_fallacy).
The observation that human subjects seem to assign higher probability to joint
events than a single event. Which is weird because the probability of two
events at the same time (conjunction) is always less than or equal to the
probability of a single event on its own.

How does the Bayesian brain hypothesis deal with this fallacy? It seems to me
that nothing based on classical probability can explain this fallacy. So
either the observation that humans can assign higher probability to joint
events is wrong or human decision making isn't exactly probabilistic (in the
classical sense, can't rule out exotic probabilistic approaches).

EDIT: As several folks have commented that the conjunction fallacy can be
explained away by different arguments based on interpretation and semantic
issues. Indeed, the original Linda problem was susceptible to these issues.
However, since then several researchers have tried to study this effect more
carefully and it seems to still persist. An example that I'm aware of is the
following
[https://link.springer.com/article/10.3758/BF03195280](https://link.springer.com/article/10.3758/BF03195280)
where the authors used unambiguous language and a betting paradigm, but still
found the effect. Again, this is most likely not fool proof. Regardless, I do
not think the fallacy can be trivially explained away as an effect of
ambiguous language.

~~~
Scea91
Regarding the Conjunction fallacy my theory is that many people who are not
used to math problems implicitly modify the question based on the context.

Instead of choosing from options:

1) Linda is A

2) Linda is A and B

they might actually understand the first statement in the context of the
second statement as:

1) Linda is A and not B

~~~
jonathanstrange
No, that's not what's going on. The reason for the fallacy is that we tend to
find more detailed stories more convincing than less detailed stories.

However, not everybody, you can be trained against that. I've heard that
police interrogators are less prone to this fallacy because they know that
liars who had time to prepare often add dozens of details to their story that
no ordinary person would remember.

~~~
may_be_useful
> 'fallacy is that we tend to find more detailed stories more convincing'

Anecdotic: Somebody asked: "Why do I feel often that angry, when I get a
'Typ5-Answer'?" (With the background an TYp5-Answer is located in the field of
the manipulation of (someones) reality.

HINT: Typ1-Answer: labeling of 'Objects' / Type2-Answer: naming of coherencies
/ Ty ....(-;

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gooseus
I'm currently reading _The Book of Why_ by Judea Pearl and I think that he
makes that claim that our brains are Bayesian and then some.

Haven't finished yet, he gets into artificial intelligence in the next few
chapters, but he seems to make the claim that our brains work by doing a
number of computations involved in causal inference beyond just Bayesian
inference, such as subconsciously constructing causal diagrams and using them
for causal inference including asking questions about counterfactual
scenarios.

Would be interested to hear if anyone else who has read this book can help
elaborate on this some.

~~~
eli_gottlieb
Judea Pearl continues to insist on causal diagrams, but the rest of us have
moved on to probabilistic programs ;-).

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analog31
My understanding of Bayesian thinking is that we form new beliefs that are a
function of our prior _beliefs_ plus new evidence. That's my interpretation of
the article.

Another way of thinking is to form new beliefs that are a function of prior
_evidence_ plus new evidence, e.g., by setting all old beliefs aside and
starting afresh with the complete body of available evidence.

It's not clear to me that these two methods produce the same results, though I
can't think of a counterexample. But to the extent that our brains probably
remember both beliefs and evidence, we are not probably not fully Bayesian.

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wnoise
See also the book _Surfing Uncertainty_ ([https://www.amazon.com/Surfing-
Uncertainty-Prediction-Action...](https://www.amazon.com/Surfing-Uncertainty-
Prediction-Action-Embodied/dp/0190217014/)) which convincingly details many
brain subsystems as approximating Bayesian updates.

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sunstone
Yes of course it is. Experience allows you to make decisions without having a
statistically valid sample all the time.

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gregw2
Are our brains Bayesian?

1990s Internet debater #1: "The plural of anecdote is not data"

2010s Internet debater #2: "True, but it does make a good bayesian prior"

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User23
Do our brains use a reasoning process invented by our brains?

~~~
zby
Discovered not invented.

~~~
User23
Does it exist somewhere in a platonic realm of forms?

~~~
jamesrcole
If our brains are Bayesian, evolution is what invented it.

~~~
User23
When I studied biology it was drilled into us that evolution doesn't have
agency. Has that changed?

~~~
coldtea
You don't need to have "agency" to invent.

LSD and sticky notes were invented by accident -- as were tons of other
things.

Sure, one could add several pedantic reservations here, if they wanted to be
thick on purpose, but the meaning of the parent's statement is clear. This
series of passive aggressive counter-questions seems to violate the principle
of charity.

~~~
User23
It's good that you are concerned with the principle of charity, perhaps you
should apply it here?

It's pretty obvious that evolution didn't "invent" anything because accident
or not, to invent requires an originator or discoverer which is to say an
entity with agency. It's as absurd as saying relativity invented black holes.

~~~
coldtea
> _It 's pretty obvious that evolution didn't "invent" anything because
> accident or not, to invent requires an originator or discoverer which is to
> say an entity with agency._

And yet everybody understood what the parent means, which is that it was
created by an evolutionary process.

And also everybody understands that the pedantic minutiae of whether "invent"
can be used here is beside the actual point the parent makes.

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throwaway487548
This is actually an idiotic question. The molecular biology does not employ a
concept of a number (or any concepts whatsoever in principle), since this
requires an intelligent observer (to form the abstract notion of a number)
which is not available at that level.

The "concrete", real-world biological systems, including our brains, however
employs frequencies and "weights", which corresponds to wideness of a pathway,
which does not require any numbers or counting.

 _Mother Nature Does Not Count_ (and it does not compute any probabilities, of
course). Higher level intellect does.

Math and logic are superimposed on the Universe and Nature. It is naive to
assume that the Universe and Nature is based on math and logic, as ancient
Greek views suppose.

Yes, there is basis behind Modus Ponens - in a certain conditions having Hs
and Os inevitably leads to H2Os because universe has its laws, and because it
has its laws it produces certain regularities and certain patterns which could
be matched and even generalized by an intelligent observer, but it is not the
other way around.

~~~
cannabis_sam
>Math and logic are superimposed on the Universe and Nature. It is naive to
assume that the Universe and Nature is based on math and logic, as ancient
Greek views suppose.

I think it’s more naive to think that the question has been settled..

[https://en.m.wikipedia.org/wiki/Mathematical_universe_hypoth...](https://en.m.wikipedia.org/wiki/Mathematical_universe_hypothesis)

~~~
throwaway487548
It depends on who is asking. If it is a "good" philosopher, who is in on the
quest to unveil the nature and laws of what is, then it is settled.

If, however, you are fond of joggling with abstractions and of studying of
philosophers themselves and various philosophical systems (instead of what is)
then, of course, you could put together yet another pile of abstractions and
even systematically compare it with another pile of abstractions, and so on.
Lots of people do.

Universe is one (at least we and everything else is bound by this one single
unfolding process we call Universe) while abstractions are infinite, and most
of them are disconnected from what is - they generalize nothing but other
disconnected abstractions.

