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The Brain as a Universal Learning Machine

76 jacob_cannell 24 June 2015 09:45PM

This article presents an emerging architectural hypothesis of the brain as a biological implementation of a Universal Learning Machine.  I present a rough but complete architectural view of how the brain works under the universal learning hypothesis.  I also contrast this new viewpoint - which comes from computational neuroscience and machine learning - with the older evolved modularity hypothesis popular in evolutionary psychology and the heuristics and biases literature.  These two conceptions of the brain lead to very different predictions for the likely route to AGI, the value of neuroscience, the expected differences between AGI and humans, and thus any consequent safety issues and dependent strategies.

Art generated by an artificial neural net

(The image above is from a recent mysterious post to r/machinelearning, probably from a Google project that generates art based on a visualization tool used to inspect the patterns learned by convolutional neural networks.  I am especially fond of the wierd figures riding the cart in the lower left. )

  1. Intro: Two viewpoints on the Mind
  2. Universal Learning Machines
  3. Historical Interlude
  4. Dynamic Rewiring
  5. Brain Architecture (the whole brain in one picture and a few pages of text)
  6. The Basal Ganglia
  7. Implications for AGI
  8. Conclusion

 

Intro: Two Viewpoints on the Mind

Few discoveries are more irritating than those that expose the pedigree of ideas.

-- Lord Acton (probably)

Less Wrong is a site devoted to refining the art of human rationality, where rationality is based on an idealized conceptualization of how minds should or could work.  Less Wrong and its founding sequences draws heavily on the heuristics and biases literature in cognitive psychology and related work in evolutionary psychology.  More specifically the sequences build upon a specific cluster in the space of cognitive theories, which can be identified in particular with the highly influential "evolved modularity" perspective of Cosmides and Tooby.

From Wikipedia:

Evolutionary psychologists propose that the mind is made up of genetically influenced and domain-specific[3] mental algorithms or computational modules, designed to solve specific evolutionary problems of the past.[4] 

From "Evolutionary Psychology and the Emotions":[5]

An evolutionary perspective leads one to view the mind as a crowded zoo of evolved, domain-specific programs.  Each is functionally specialized for solving a different adaptive problem that arose during hominid evolutionary history, such as face recognition, foraging, mate choice, heart rate regulation, sleep management, or predator vigilance, and each is activated by a different set of cues from the environment.

If you imagine these general theories or perspectives on the brain/mind as points in theory space, the evolved modularity cluster posits that much of the machinery of human mental algorithms is largely innate.  General learning - if it exists at all - exists only in specific modules; in most modules learning is relegated to the role of adapting existing algorithms and acquiring data; the impact of the information environment is de-emphasized.  In this view the brain is a complex messy cludge of evolved mechanisms.

There is another viewpoint cluster, more popular in computational neuroscience (especially today), that is almost the exact opposite of the evolved modularity hypothesis.  I will rebrand this viewpoint the "universal learner" hypothesis, aka the "one learning algorithm" hypothesis (the rebranding is justified mainly by the inclusion of some newer theories and evidence for the basal ganglia as a 'CPU' which learns to control the cortex).  The roots of the universal learning hypothesis can be traced back to Mountcastle's discovery of the simple uniform architecture of the cortex.[6]

The universal learning hypothesis proposes that all significant mental algorithms are learned; nothing is innate except for the learning and reward machinery itself (which is somewhat complicated, involving a number of systems and mechanisms), the initial rough architecture (equivalent to a prior over mindspace), and a small library of simple innate circuits (analogous to the operating system layer in a computer).  In this view the mind (software) is distinct from the brain (hardware).  The mind is a complex software system built out of a general learning mechanism.

In simplification, the main difference between these viewpoints is the relative quantity of domain specific mental algorithmic information specified in the genome vs that acquired through general purpose learning during the organism's lifetime.  Evolved modules vs learned modules.

When you have two hypotheses or viewpoints that are almost complete opposites this is generally a sign that the field is in an early state of knowledge; further experiments typically are required to resolve the conflict.

It has been about 25 years since Cosmides and Tooby began to popularize the evolved modularity hypothesis.  A number of key neuroscience experiments have been performed since then which support the universal learning hypothesis (reviewed later in this article).  

Additional indirect support comes from the rapid unexpected success of Deep Learning[7], which is entirely based on building AI systems using simple universal learning algorithms (such as Stochastic Gradient Descent or other various approximate Bayesian methods[8][9][10][11]) scaled up on fast parallel hardware (GPUs).  Deep Learning techniques have quickly come to dominate most of the key AI benchmarks including vision[12], speech recognition[13][14], various natural language tasks, and now even ATARI [15] - proving that simple architectures (priors) combined with universal learning is a path (and perhaps the only viable path) to AGI. Moreover, the internal representations that develop in some deep learning systems are structurally and functionally similar to representations in analogous regions of biological cortex[16].

To paraphrase Feynman: to truly understand something you must build it. 

In this article I am going to quickly introduce the abstract concept of a universal learning machine, present an overview of the brain's architecture as a specific type of universal learning machine, and finally I will conclude with some speculations on the implications for the race to AGI and AI safety issues in particular.

Universal Learning Machines

A universal learning machine is a simple and yet very powerful and general model for intelligent agents.  It is an extension of a general computer - such as Turing Machine - amplified with a universal learning algorithm.  Do not view this as my 'big new theory' - it is simply an amalgamation of a set of related proposals by various researchers.

An initial untrained seed ULM can be defined by 1.) a prior over the space of models (or equivalently, programs), 2.) an initial utility function, and 3.) the universal learning machinery/algorithm.  The machine is a real-time system that processes an input sensory/observation stream and produces an output motor/action stream to control the external world using a learned internal program that is the result of continuous self-optimization.

There is of course always room to smuggle in arbitrary innate functionality via the prior, but in general the prior is expected to be extremely small in bits in comparison to the learned model.

The key defining characteristic of a ULM is that it uses its universal learning algorithm for continuous recursive self-improvement with regards to the utility function (reward system).  We can view this as second (and higher) order optimization: the ULM optimizes the external world (first order), and also optimizes its own internal optimization process (second order), and so on.  Without loss of generality, any system capable of computing a large number of decision variables can also compute internal self-modification decisions.

Conceptually the learning machinery computes a probability distribution over program-space that is proportional to the expected utility distribution.  At each timestep it receives a new sensory observation and expends some amount of computational energy to infer an updated (approximate) posterior distribution over its internal program-space: an approximate 'Bayesian' self-improvement.

The above description is intentionally vague in the right ways to cover the wide space of possible practical implementations and current uncertainty.  You could view AIXI as a particular formalization of the above general principles, although it is also as dumb as a rock in any practical sense and has other potential theoretical problems.  Although the general idea is simple enough to convey in the abstract, one should beware of concise formal descriptions: practical ULMs are too complex to reduce to a few lines of math.

A ULM inherits the general property of a Turing Machine that it can compute anything that is computable, given appropriate resources.  However a ULM is also more powerful than a TM.  A Turing Machine can only do what it is programmed to do.  A ULM automatically programs itself.

If you were to open up an infant ULM - a machine with zero experience - you would mainly just see the small initial code for the learning machinery.  The vast majority of the codestore starts out empty - initialized to noise.  (In the brain the learning machinery is built in at the hardware level for maximal efficiency).

Theoretical turing machines are all qualitatively alike, and are all qualitatively distinct from any non-universal machine.  Likewise for ULMs.  Theoretically a small ULM is just as general/expressive as a planet-sized ULM.  In practice quantitative distinctions do matter, and can become effectively qualitative.

Just as the simplest possible Turing Machine is in fact quite simple, the simplest possible Universal Learning Machine is also probably quite simple.  A couple of recent proposals for simple universal learning machines include the Neural Turing Machine[16] (from Google DeepMind), and Memory Networks[17].  The core of both approaches involve training an RNN to learn how to control a memory store through gating operations. 

Historical Interlude

At this point you may be skeptical: how could the brain be anything like a universal learner?  What about all of the known innate biases/errors in human cognition?  I'll get to that soon, but let's start by thinking of a couple of general experiments to test the universal learning hypothesis vs the evolved modularity hypothesis.

In a world where the ULH is mostly correct, what do we expect to be different than in worlds where the EMH is mostly correct?

One type of evidence that would support the ULH is the demonstration of key structures in the brain along with associated wiring such that the brain can be shown to directly implement some version of a ULM architecture.

Another type of indirect evidence that would help discriminate the two theories would be evidence that the brain is capable of general global optimization, and that complex domain specific algorithms/circuits mostly result from this process.  If on the other hand the brain is only capable of constrained/local optimization, then most of the complexity must instead be innate - the result of global optimization in evolutionary deeptime.  So in essence it boils down to the optimization capability of biological learning vs biological evolution.

From the perspective of the EMH, it is not sufficient to demonstrate that there are things that brains can not learn in practice - because those simply could be quantitative limitations.  Demonstrating that an intel 486 can't compute some known computable function in our lifetimes is not proof that the 486 is not a Turing Machine.

Nor is it sufficient to demonstrate that biases exist: a ULM is only 'rational' to the extent that its observational experience and learning machinery allows (and to the extent one has the correct theory of rationality).  In fact, the existence of many (most?) biases intrinsically depends on the EMH - based on the implicit assumption that some cognitive algorithms are innate.  If brains are mostly ULMs then most cognitive biases dissolve, or become learning biases - for if all cognitive algorithms are learned, then evidence for biases is evidence for cognitive algorithms that people haven't had sufficient time/energy/motivation to learn.  (This does not imply that intrinsic limitations/biases do not exist or that the study of cognitive biases is a waste of time; rather the ULH implies that educational history is what matters most)

The genome can only specify a limited amount of information.  The question is then how much of our advanced cognitive machinery for things like facial recognition, motor planning, language, logic, planning, etc. is innate vs learned.  From evolution's perspective there is a huge advantage to preloading the brain with innate algorithms so long as said algorithms have high expected utility across the expected domain landscape.  

On the other hand, evolution is also highly constrained in a bit coding sense: every extra bit of code costs additional energy for the vast number of cellular replication events across the lifetime of the organism.  Low code complexity solutions also happen to be exponentially easier to find.  These considerations seem to strongly favor the ULH but they are difficult to quantify.

Neuroscientists have long known that the brain is divided into physical and functional modules.  These modular subdivisions were discovered a century ago by Brodmann.  Every time neuroscientists opened up a new brain, they saw the same old cortical modules in the same old places doing the same old things.  The specific layout of course varied from species to species, but the variations between individuals are minuscule. This evidence seems to strongly favor the EMH.

Throughout most of the 90's up into the 2000's, evidence from computational neuroscience models and AI were heavily influenced by - and unsurprisingly - largely supported the EMH.  Neural nets and backprop were known of course since the 1980's and worked on small problems[18], but at the time they didn't scale well - and there was no theory to suggest they ever would.  

Theory of the time also suggested local minima would always be a problem (now we understand that local minima are not really the main problem[19], and modern stochastic gradient descent methods combined with highly overcomplete models and stochastic regularization[20] are effectively global optimizers that can often handle obstacles such as local minima and saddle points[21]).  

The other related historical criticism rests on the lack of biological plausibility for backprop style gradient descent.  (There is as of yet little consensus on how the brain implements the equivalent machinery, but target propagation is one of the more promising recent proposals[22][23].)

Many AI researchers are naturally interested in the brain, and we can see the influence of the EMH in much of the work before the deep learning era.  HMAX is a hierarchical vision system developed in the late 90's by Poggio et al as a working model of biological vision[24].  It is based on a preconfigured hierarchy of modules, each of which has its own mix of innate features such as gabor edge detectors along with a little bit of local learning.  It implements the general idea that complex algorithms/features are innate - the result of evolutionary global optimization - while neural networks (incapable of global optimization) use hebbian local learning to fill in details of the design.

Dynamic Rewiring

In a groundbreaking study from 2000 published in Nature, Sharma et al successfully rewired ferret retinal pathways to project into the auditory cortex instead of the visual cortex.[25]  The result: auditory cortex can become visual cortex, just by receiving visual data!  Not only does the rewired auditory cortex develop the specific gabor features characteristic of visual cortex; the rewired cortex also becomes functionally visual. [26] True, it isn't quite as effective as normal visual cortex, but that could also possibly be an artifact of crude and invasive brain rewiring surgery.

The ferret study was popularized by the book On Intelligence by Hawkins in 2004 as evidence for a single cortical learning algorithm.  This helped percolate the evidence into the wider AI community, and thus probably helped in setting up the stage for the deep learning movement of today.  The modern view of the cortex is that of a mostly uniform set of general purpose modules which slowly become recruited for specific tasks and filled with domain specific 'code' as a result of the learning (self optimization) process.

The next key set of evidence comes from studies of atypical human brains with novel extrasensory powers.  In 2009 Vuillerme et al showed that the brain could automatically learn to process sensory feedback rendered onto the tongue[27].  This research was developed into a complete device that allows blind people to develop primitive tongue based vision.

In the modern era some blind humans have apparently acquired the ability to perform echolocation (sonar), similar to cetaceans.  In 2011 Thaler et al used MRI and PET scans to show that human echolocators use diverse non-auditory brain regions to process echo clicks, predominantly relying on re-purposed 'visual' cortex.[27] 

The echolocation study in particular helps establish the case that the brain is actually doing global, highly nonlocal optimization - far beyond simple hebbian dynamics.  Echolocation is an active sensing strategy that requires very low latency processing, involving complex timed coordination between a number of motor and sensory circuits - all of which must be learned.

Somehow the brain is dynamically learning how to use and assemble cortical modules to implement mental algorithms: everyday tasks such as visual counting, comparisons of images or sounds, reading, etc - all are task which require simple mental programs that can shuffle processed data between modules (some or any of which can also function as short term memory buffers).

To explain this data, we should be on the lookout for a system in the brain that can learn to control the cortex - a general system that dynamically routes data between different brain modules to solve domain specific tasks.

But first let's take a step back and start with a high level architectural view of the entire brain to put everything in perspective.

Brain Architecture

Below is a circuit diagram for the whole brain.  Each of the main subsystems work together and are best understood together.  You can probably get a good high level extremely coarse understanding of the entire brain is less than one hour.

(there are a couple of circuit diagrams of the whole brain on the web, but this is the best.  From this site.)

The human brain has ~100 billion neurons and ~100 trillion synapses, but ultimately it evolved from the bottom up - from organisms with just hundreds of neurons, like the tiny brain of C. Elegans.

We know that evolution is code complexity constrained: much of the genome codes for cellular metabolism, all the other organs, and so on.  For the brain, most of its bit budget needs to be spent on all the complex neuron, synapse, and even neurotransmitter level machinery - the low level hardware foundation.

For a tiny brain with 1000 neurons or less, the genome can directly specify each connection.  As you scale up to larger brains, evolution needs to create vastly more circuitry while still using only about the same amount of code/bits.  So instead of specifying connectivity at the neuron layer, the genome codes connectivity at the module layer.  Each module can be built from simple procedural/fractal expansion of progenitor cells.

So the size of a module has little to nothing to do with its innate complexity.  The cortical modules are huge - V1 alone contains 200 million neurons in a human - but there is no reason to suspect that V1 has greater initial code complexity than any other brain module.  Big modules are built out of simple procedural tiling patterns.

Very roughly the brain's main modules can be divided into six subsystems (there are numerous smaller subsystems):

  • The neocortex: the brain's primary computational workhorse (blue/purple modules at the top of the diagram).  Kind of like a bunch of general purpose FPGA coprocessors.
  • The cerebellum: another set of coprocessors with a simpler feedforward architecture.  Specializes more in motor functionality. 
  • The thalamus: the orangish modules below the cortex.  Kind of like a relay/routing bus.
  • The hippocampal complex: the apex of the cortex, and something like the brain's database.
  • The amygdala and limbic reward system: these modules specialize in something like the value function.
  • The Basal Ganglia (green modules): the central control system, similar to a CPU.

In the interest of space/time I will focus primarily on the Basal Ganglia and will just touch on the other subsystems very briefly and provide some links to further reading.

The neocortex has been studied extensively and is the main focus of several popular books on the brain.  Each neocortical module is a 2D array of neurons (technically 2.5D with a depth of about a few dozen neurons arranged in about 5 to 6 layers).

Each cortical module is something like a general purpose RNN (recursive neural network) with 2D local connectivity.  Each neuron connects to its neighbors in the 2D array.  Each module also has nonlocal connections to other brain subsystems and these connections follow the same local 2D connectivity pattern, in some cases with some simple affine transformations.  Convolutional neural networks use the same general architecture (but they are typically not recurrent.)

Cortical modules - like artifical RNNs - are general purpose and can be trained to perform various tasks.  There are a huge number of models of the cortex, varying across the tradeoff between biological realism and practical functionality.  

Perhaps surprisingly, any of a wide variety of learning algorithms can reproduce cortical connectivity and features when trained on appropriate sensory data[27].  This is a computational proof of the one-learning-algorithm hypothesis; furthermore it illustrates the general idea that data determines functional structure in any general learning system.

There is evidence that cortical modules learn automatically (unsupervised) to some degree, and there is also some evidence that cortical modules can be trained to relearn data from other brain subsystems - namely the hippocampal complex.  The dark knowledge distillation technique in ANNs[28][29] is a potential natural analog/model of hippocampus -> cortex knowledge transfer.

Module connections are bidirectional, and feedback connections (from high level modules to low level) outnumber forward connections.  We can speculate that something like target propagation can also be used to guide or constrain the development of cortical maps (speculation).

The hippocampal complex is the root or top level of the sensory/motor hierarchy.  This short youtube video  gives a good seven minute overview of the HC.  It is like a spatiotemporal database.  It receives compressed scene descriptor streams from the sensory cortices, it stores this information in medium-term memory, and it supports later auto-associative recall of these memories.  Imagination and memory recall seem to be basically the same.  

The 'scene descriptors' take the sensible form of things like 3D position and camera orientation, as encoded in place, grid, and head direction cells.  This is basically the logical result of compressing the sensory stream, comparable to the networking data stream in a multiplayer video game.

Imagination/recall is basically just the reverse of the forward sensory coding path - in reverse mode a compact scene descriptor is expanded into a full imagined scene.  Imagined/remembered scenes activate the same cortical subnetworks that originally formed the memory (or would have if the memory was real, in the case of imagined recall).

The amygdala and associated limbic reward modules are rather complex, but look something like the brain's version of the value function for reinforcement learning.  These modules are interesting because they clearly rely on learning, but clearly the brain must specify an initial version of the value/utility function that has some minimal complexity.

As an example, consider taste.  Infants are born with basic taste detectors and a very simple initial value function for taste.  Over time the brain receives feedback from digestion and various estimators of general mood/health, and it uses this to refine the initial taste value function.  Eventually the adult sense of taste becomes considerably more complex.  Acquired taste for bitter substances - such as coffee and beer - are good examples.

The amygdala appears to do something similar for emotional learning.  For example infants are born with a simple versions of a fear response, with is later refined through reinforcement learning.  The amygdala sits on the end of the hippocampus, and it is also involved heavily in memory processing.

See also these two videos from khanacademy: one on the limbic system and amygdala (10 mins), and another on the midbrain reward system (8 mins)

 

The Basal Ganglia

 

The Basal Ganglia is a wierd looking complex of structures located in the center of the brain.  It is a conserved structure found in all vertebrates, which suggests a core functionality.  The BG is proximal to and connects heavily with the midbrain reward/limbic systems.  It also connects to the brain's various modules in the cortex/hippocampus, thalamus and the cerebellum . . . basically everything.

All of these connections form recurrent loops between associated compartmental modules in each structure: thalamocortical/hippocampal-cerebellar-basal_ganglial loops.

 

Just as the cortex and hippocampus are subdivided into modules, there are corresponding modular compartments in the thalamus, basal ganglia, and the cerebellum.  The set of modules/compartments in each main structure are all highly interconnected with their correspondents across structures, leading to the concept of distributed processing modules.

Each DPM forms a recurrent loop across brain structures (the local networks in the cortex, BG, and thalamus are also locally recurrent, whereas those in the cerebellum are not).  These recurrent loops are mostly separate, but each sub-structure also provides different opportunities for inter-loop connections.

The BG appears to be involved in essentially all higher cognitive functions.  Its core functionality is action selection via subnetwork switching.  In essence action selection is the core problem of intelligence, and it is also general enough to function as the building block of all higher functionality.  A system that can select between motor actions can also select between tasks or subgoals.  More generally, low level action selection can easily form the basis of a Turing Machine via selective routing: deciding where to route the output of thalamocortical-cerebellar modules (some of which may specialize in short term memory as in the prefrontal cortex, although all cortical modules have some short term memory capability).

There are now a number of computational models for the Basal Ganglia-Cortical system that demonstrate possible biologically plausible implementations of the general theory[28][29]; integration with the hippocampal complex leads to larger-scale systems which aim to model/explain most of higher cognition in terms of sequential mental programs[30] (of course fully testing any such models awaits sufficient computational power to run very large-scale neural nets).

For an extremely oversimplified model of the BG as a dynamic router, consider an array of N distributed modules controlled by the BG system.  The BG control network expands these N inputs into an NxN matrix.  There are N2 potential intermodular connections, each of which can be individually controlled.  The control layer reads a compressed, downsampled version of the module's hidden units as its main input, and is also recurrent.  Each output node in the BG has a multiplicative gating effect which selectively enables/disables an individual intermodular connection.  If the control layer is naively fully connected, this would require (N2)2 connections, which is only feasible for N ~ 100 modules, but sparse connectivity can substantially reduce those numbers.

It is unclear (to me), whether the BG actually implements NxN style routing as described above, or something more like 1xN or Nx1 routing, but there is general agreement that it implements cortical routing. 

Of course in actuality the BG architecture is considerably more complex, as it also must implement reinforcement learning, and the intermodular connectivity map itself is also probably quite sparse/compressed (the BG may not control all of cortex, certainly not at a uniform resolution, and many controlled modules may have a very limited number of allowed routing decisions).  Nonetheless, the simple multiplicative gating model illustrates the core idea.  

This same multiplicative gating mechanism is the core principle behind the highly successful LSTM (Long Short-Term Memory)[30] units that are used in various deep learning systems.  The simple version of the BG's gating mechanism can be considered a wider parallel and hierarchical extension of the basic LSTM architecture, where you have a parallel array of N memory cells instead of 1, and each memory cell is a large vector instead of a single scalar value.

The main advantage of the BG architecture is parallel hierarchical approximate control: it allows a large number of hierarchical control loops to update and influence each other in parallel.  It also reduces the huge complexity of general routing across the full cortex down into a much smaller-scale, more manageable routing challenge.

Implications for AGI

These two conceptions of the brain - the universal learning machine hypothesis and the evolved modularity hypothesis - lead to very different predictions for the likely route to AGI, the expected differences between AGI and humans, and thus any consequent safety issues and strategies.

In the extreme case imagine that the brain is a pure ULM, such that the genetic prior information is close to zero or is simply unimportant.  In this case it is vastly more likely that successful AGI will be built around designs very similar to the brain, as the ULM architecture in general is the natural ideal, vs the alternative of having to hand engineer all of the AI's various cognitive mechanisms.

In reality learning is computationally hard, and any practical general learning system depends on good priors to constrain the learning process (essentially taking advantage of previous knowledge/learning).  The recent and rapid success of deep learning is strong evidence for how much prior information is ideal: just a little.  The prior in deep learning systems takes the form of a compact, small set of hyperparameters that control the learning process and specify the overall network architecture (an extremely compressed prior over the network topology and thus the program space).

The ULH suggests that most everything that defines the human mind is cognitive software rather than hardware: the adult mind (in terms of algorithmic information) is 99.999% a cultural/memetic construct.  Obviously there are some important exceptions: infants are born with some functional but very primitive sensory and motor processing 'code'.  Most of the genome's complexity is used to specify the learning machinery, and the associated reward circuitry.  Infant emotions appear to simplify down to a single axis of happy/sad; differentiation into the more subtle vector space of adult emotions does not occur until later in development.

If the mind is software, and if the brain's learning architecture is already universal, then AGI could - by default - end up with a similar distribution over mindspace, simply because it will be built out of similar general purpose learning algorithms running over the same general dataset.  We already see evidence for this trend in the high functional similarity between the features learned by some machine learning systems and those found in the cortex.

Of course an AGI will have little need for some specific evolutionary features: emotions that are subconsciously broadcast via the facial muscles is a quirk unnecessary for an AGI - but that is a rather specific detail.

The key takeway is that the data is what matters - and in the end it is all that matters.  Train a universal learner on image data and it just becomes a visual system.  Train it on speech data and it becomes a speech recognizer.  Train it on ATARI and it becomes a little gamer agent.  

Train a universal learner on the real world in something like a human body and you get something like the human mind.  Put a ULM in a dolphin's body and echolocation is the natural primary sense, put a ULM in a human body with broken visual wiring and you can also get echolocation. 

Control over training is the most natural and straightforward way to control the outcome.  

To create a superhuman AI driver, you 'just' need to create a realistic VR driving sim and then train a ULM in that world (better training and the simple power of selective copying leads to superhuman driving capability).

So to create benevolent AGI, we should think about how to create virtual worlds with the right structure, how to educate minds in those worlds, and how to safely evaluate the results.

One key idea - which I proposed five years ago is that the AI should not know it is in a sim. 

New AI designs (world design + architectural priors + training/education system) should be tested first in the safest virtual worlds: which in simplification are simply low tech worlds without computer technology.  Design combinations that work well in safe low-tech sandboxes are promoted to less safe high-tech VR worlds, and then finally the real world.

A key principle of a secure code sandbox is that the code you are testing should not be aware that it is in a sandbox.  If you violate this principle then you have already failed.  Yudkowsky's AI box thought experiment assumes the violation of the sandbox security principle apriori and thus is something of a distraction. (the virtual sandbox idea was most likely discussed elsewhere previously, as Yudkowsky indirectly critiques a strawman version of the idea via this sci-fi story).  

The virtual sandbox approach also combines nicely with invisible thought monitors, where the AI's thoughts are automatically dumped to searchable logs.

Of course we will still need a solution to the value learning problem.  The natural route with brain-inspired AI is to learn the key ideas behind value acquisition in humans to help derive an improved version of something like inverse reinforcement learning and or imitation learning[31] - an interesting topic for another day.

Conclusion

Ray Kurzweil has been predicting for decades that AGI will be built by reverse engineering the brain, and this particular prediction is not especially unique - this has been a popular position for quite a while.  My own investigation of neuroscience and machine learning led me to a similar conclusion some time ago.  

The recent progress in deep learning, combined with the emerging modern understanding of the brain, provide further evidence that AGI could arrive around the time when we can build and train ANNs with similar computational power as measured very roughly in terms of neuron/synapse counts.  In general the evidence from the last four years or so supports Hanson's viewpoint from the Foom debate.  More specifically, his general conclusion:

Future superintelligences will exist, but their vast and broad mental capacities will come mainly from vast mental content and computational resources. By comparison, their general architectural innovations will be minor additions.

The ULH supports this conclusion.

Current ANN engines can already train and run models with around 10 million neurons and 10 billion (compressed/shared) synapses on a single GPU, which suggests that the goal could soon be within the reach of a large organization.  Furthermore, Moore's Law for GPUs still has some steam left, and software advances are currently improving simulation performance at a faster rate than hardware.  These trends implies that Anthropomorphic/Neuromorphic AGI could be surprisingly close, and may appear suddenly.

What kind of leverage can we exert on a short timescale?

 

Taking the reins at MIRI

59 So8res 03 June 2015 11:52PM

Hi all. In a few hours I'll be taking over as executive director at MIRI. The LessWrong community has played a key role in MIRI's history, and I hope to retain and build your support as (with more and more people joining the global conversation about long-term AI risks & benefits) MIRI moves towards the mainstream.

Below I've cross-posted my introductory post on the MIRI blog, which went live a few hours ago. The short version is: there are very exciting times ahead, and I'm honored to be here. Many of you already know me in person or through my blog posts, but for those of you who want to get to know me better, I'll be running an AMA on the effective altruism forum at 3PM Pacific on Thursday June 11th.

I extend to all of you my thanks and appreciation for the support that so many members of this community have given to MIRI throughout the years.

continue reading »

The Unfriendly Superintelligence next door

45 jacob_cannell 02 July 2015 06:46PM

Markets are powerful decentralized optimization engines - it is known.  Liberals see the free market as a kind of optimizer run amuck, a dangerous superintelligence with simple non-human values that must be checked and constrained by the government - the friendly SI.  Conservatives just reverse the narrative roles.

In some domains, where the incentive structure aligns with human values, the market works well.  In our current framework, the market works best for producing gadgets. It does not work so well for pricing intangible information, and most specifically it is broken when it comes to health.

We treat health as just another gadget problem: something to be solved by pills.  Health is really a problem of knowledge; it is a computational prediction problem.  Drugs are useful only to the extent that you can package the results of new knowledge into a pill and patent it.  If you can't patent it, you can't profit from it.

So the market is constrained to solve human health by coming up with new patentable designs for mass-producible physical objects which go into human bodies.  Why did we add that constraint - thou should solve health, but thou shalt only use pills?  (Ok technically the solutions don't have to be ingestible, but that's a detail.)

The gadget model works for gadgets because we know how gadgets work - we built them, after all.  The central problem with health is that we do not completely understand how the human body works - we did not build it.  Thus we should be using the market to figure out how the body works - completely - and arguably we should be allocating trillions of dollars towards that problem.

The market optimizer analogy runs deeper when we consider the complexity of instilling values into a market.  Lawmakers cannot program the market with goals directly, so instead they attempt to engineer desireable behavior by ever more layers and layers of constraints.  Lawmakers are deontologists.

As an example, consider the regulations on drug advertising.  Big pharma is unsafe - its profit function does not encode anything like "maximize human health and happiness" (which of course itself is an oversimplification).  If allowed to its own devices, there are strong incentives to sell subtly addictive drugs, to create elaborate hyped false advertising campaigns, etc.  Thus all the deontological injunctions.  I take that as a strong indicator of a poor solution - a value alignment failure.

What would healthcare look like in a world where we solved the alignment problem?

To solve the alignment problem, the market's profit function must encode long term human health and happiness.  This really is a mechanism design problem - its not something lawmakers are even remotely trained or qualified for.  A full solution is naturally beyond the scope of a little blog post, but I will sketch out the general idea.

To encode health into a market utility function, first we create financial contracts with an expected value which captures long-term health.  We can accomplish this with a long-term contract that generates positive cash flow when a human is healthy, and negative when unhealthy - basically an insurance contract.  There is naturally much complexity in getting those contracts right, so that they measure what we really want.  But assuming that is accomplished, the next step is pretty simple - we allow those contracts to trade freely on an open market.

There are some interesting failure modes and considerations that are mostly beyond scope but worth briefly mentioning.  This system probably needs to be asymmetric.  The transfers on poor health outcomes should partially go to cover medical payments, but it may be best to have a portion of the wealth simply go to nobody/everybody - just destroyed.

In this new framework, designing and patenting new drugs can still be profitable, but it is now put on even footing with preventive medicine.  More importantly, the market can now actually allocate the correct resources towards long term research.

To make all this concrete, let's use an example of a trillion dollar health question - one that our current system is especially ill-posed to solve:

What are the long-term health effects of abnormally low levels of solar radiation?  What levels of sun exposure are ideal for human health?

This is a big important question, and you've probably read some of the hoopla and debate about vitamin D.  I'm going to soon briefly summarize a general abstract theory, one that I would bet heavily on if we lived in a more rational world where such bets were possible.

In a sane world where health is solved by a proper computational market, I could make enormous - ridiculous really - amounts of money if I happened to be an early researcher who discovered the full health effects of sunlight.  I would bet on my theory simply by buying up contracts for individuals/demographics who had the most health to gain by correcting their sunlight deficiency.  I would then publicize the theory and evidence, and perhaps even raise a heap pile of money to create a strong marketing engine to help ensure that my investments - my patients - were taking the necessary actions to correct their sunlight deficiency.  Naturally I would use complex machine learning models to guide the trading strategy.

Now, just as an example, here is the brief 'pitch' for sunlight.

If we go back and look across all of time, there is a mountain of evidence which more or less screams - proper sunlight is important to health.  Heliotherapy has a long history.

Humans, like most mammals, and most other earth organisms in general, evolved under the sun.  A priori we should expect that organisms will have some 'genetic programs' which take approximate measures of incident sunlight as an input.  The serotonin -> melatonin mediated blue-light pathway is an example of one such light detecting circuit which is useful for regulating the 24 hour circadian rhythm.

The vitamin D pathway has existed since the time of algae such as the Coccolithophore.  It is a multi-stage pathway that can measure solar radiation over a range of temporal frequencies.  It starts with synthesis of fat soluble cholecalciferiol which has a very long half life measured in months. [1] [2]

The rough pathway is:

  • Cholecalciferiol (HL ~ months) becomes 
  • 25(OH)D (HL ~ 15 days) which finally becomes 
  • 1,25(OH)2 D (HL ~ 15 hours)

The main recognized role for this pathway in regards to human health - at least according to the current Wikipedia entry - is to enhance "the internal absorption of calcium, iron, magnesium, phosphate, and zinc".  Ponder that for a moment.

Interestingly, this pathway still works as a general solar clock and radiation detector for carnivores - as they can simply eat the precomputed measurement in their diet.

So, what is a long term sunlight detector useful for?  One potential application could be deciding appropriate resource allocation towards DNA repair.  Every time an organism is in the sun it is accumulating potentially catastrophic DNA damage that must be repaired when the cell next divides.  We should expect that genetic programs would allocate resources to DNA repair and various related activities dependent upon estimates of solar radiation.

I should point out - just in case it isn't obvious - that this general idea does not imply that cranking up the sunlight hormone to insane levels will lead to much better DNA/cellular repair.  There are always tradeoffs, etc.

One other obvious use of a long term sunlight detector is to regulate general strategic metabolic decisions that depend on the seasonal clock - especially for organisms living far from the equator.  During the summer when food is plentiful, the body can expect easy calories.  As winter approaches calories become scarce and frugal strategies are expected.

So first off we'd expect to see a huge range of complex effects showing up as correlations between low vit D levels and various illnesses, and specifically illnesses connected to DNA damage (such as cancer) and or BMI.  

Now it turns out that BMI itself is also strongly correlated with a huge range of health issues.  So the first key question to focus on is the relationship between vit D and BMI.  And - perhaps not surprisingly - there is pretty good evidence for such a correlation [3][4] , and this has been known for a while.

Now we get into the real debate.  Numerous vit D supplement intervention studies have now been run, and the results are controversial.  In general the vit D experts (such as my father, who started the vit D council, and publishes some related research[5]) say that the only studies that matter are those that supplement at high doses sufficient to elevate vit D levels into a 'proper' range which substitutes for sunlight, which in general requires 5000 IU day on average - depending completely on genetics and lifestyle (to the point that any one-size-fits all recommendation is probably terrible).

The mainstream basically ignores all that and funds studies at tiny RDA doses - say 400 IU or less - and then they do meta-analysis over those studies and conclude that their big meta-analysis, unsurprisingly, doesn't show a statistically significant effect.  However, these studies still show small effects.  Often the meta-analysis is corrected for BMI, which of course also tends to remove any vit D effect, to the extent that low vit D/sunlight is a cause of both weight gain and a bunch of other stuff.

So let's look at two studies for vit D and weight loss.

First, this recent 2015 study of 400 overweight Italians (sorry the actual paper doesn't appear to be available yet) tested vit D supplementation for weight loss.  The 3 groups were (0 IU/day, ~1,000 IU / day, ~3,000 IU/day).  The observed average weight loss was (1 kg, 3.8 kg, 5.4 kg). I don't know if the 0 IU group received a placebo.  Regardless, it looks promising.

On the other hand, this 2013 meta-analysis of 9 studies with 1651 adults total (mainly women) supposedly found no significant weight loss effect for vit D.  However, the studies used between 200 IU/day to 1,100 IU/day, with most between 200 to 400 IU.  Five studies used calcium, five also showed weight loss (not necessarily the same - unclear).  This does not show - at all - what the study claims in its abstract.

In general, medical researchers should not be doing statistics.  That is a job for the tech industry.

Now the vit D and sunlight issue is complex, and it will take much research to really work out all of what is going on.  The current medical system does not appear to be handling this well - why?  Because there is insufficient financial motivation.

Is Big Pharma interested in the sunlight/vit D question?  Well yes - but only to the extent that they can create a patentable analogue!  The various vit D analogue drugs developed or in development is evidence that Big Pharma is at least paying attention.  But assuming that the sunlight hypothesis is mainly correct, there is very little profit in actually fixing the real problem.

There is probably more to sunlight that just vit D and serotonin/melatonin.  Consider the interesting correlation between birth month and a number of disease conditions[6].  Perhaps there is a little grain of truth to astrology after all.

Thus concludes my little vit D pitch.  

In a more sane world I would have already bet on the general theory.  In a really sane world it would have been solved well before I would expect to make any profitable trade.  In that rational world you could actually trust health advertising, because you'd know that health advertisers are strongly financially motivated to convince you of things actually truly important for your health.

Instead of charging by the hour or per treatment, like a mechanic, doctors and healthcare companies should literally invest in their patients long-term health, and profit from improvements to long term outcomes.  The sunlight health connection is a trillion dollar question in terms of medical value, but not in terms of exploitable profits in today's reality.  In a properly constructed market, there would be enormous resources allocated to answer these questions, flowing into legions of profit motivated startups that could generate billions trading on computational health financial markets, all without selling any gadgets.

So in conclusion: the market could solve health, but only if we allowed it to and only if we setup appropriate financial mechanisms to encode the correct value function.  This is the UFAI problem next door.


MIRI's 2015 Summer Fundraiser!

30 So8res 21 July 2015 12:21AM

It's safe to say that this past year exceeded a lot of people's expectations.

Twelve months ago, Nick Bostrom's Superintelligence had just come out. Questions about the long-term risks and benefits of smarter-than-human AI systems were nearly invisible in mainstream discussions of AI's social impact.

Twelve months later, we live in a world where Bill Gates is confused by why so many researchers aren't using Superintelligence as a guide to the questions we should be asking about AI's future as a field.

Following a conference in Puerto Rico that brought together the leading organizations studying long-term AI risk (MIRI, FHI, CSER) and top AI researchers in academia (including Stuart Russell, Tom Mitchell, Bart Selman, and the Presidents of AAAI and IJCAI) and industry (including representatives from Google DeepMind and Vicarious), we've seen Elon Musk donate $10M to a grants program aimed at jump-starting the field of long-term AI safety research; we've seen the top AI and machine learning conferences (AAAI, IJCAI, and NIPS) announce their first-ever workshops or discussions on AI safety and ethics; and we've seen a panel discussion on superintelligence at ITIF, the leading U.S. science and technology think tank. (I presented a paper at the AAAI workshop, I spoke on the ITIF panel, and I'll be at NIPS.)

As researchers begin investigating this area in earnest, MIRI is in an excellent position, with a developed research agenda already in hand. If we can scale up as an organization then we have a unique chance to shape the research priorities and methods of this new paradigm in AI, and direct this momentum in useful directions.

This is a big opportunity. MIRI is already growing and scaling its research activities, but the speed at which we scale in the coming months and years depends heavily on our available funds.

For that reason, MIRI is starting a six-week fundraiser aimed at increasing our rate of growth.

 

— Live Progress Bar 

Donate Now

 

This time around, rather than running a matching fundraiser with a single fixed donation target, we'll be letting you help choose MIRI's course based on the details of our funding situation and how we would make use of marginal dollars.

In particular, our plans can scale up in very different ways depending on which of these funding targets we are able to hit:

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Is Scott Alexander bad at math?

29 JonahSinick 04 May 2015 05:11AM

This post is a third installment to the sequence that I started with The Truth About Mathematical Ability and Innate Mathematical Ability. I begin to discuss the role of aesthetics in math. 

There was strong interest in the first two posts in my sequence, and I apologize for the long delay. The reason for it is that I've accumulated hundreds of pages of relevant material in draft form, and have struggled with how to organize such a large body of material. I still don't know what's best, but since people have been asking, I decided to continue posting on the subject, even if I don't have my thoughts as organized as I'd like. I'd greatly welcome and appreciate any comments, but I won't have time to respond to them individually, because I already have my hands full with putting my hundreds of pages of writing in public form.

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How my social skills went from horrible to mediocre

28 JonahSinick 19 May 2015 11:29PM

Over the past few months, I've become aware that my understanding of social reality had been distorted to an extreme degree. It took 29 years for me to figure out what was going on, but I finally now understand.

The situation is very simple: The amount of time that I put into interacting within typical social contexts was very small, so I didn't get enough feedback to realize that I had a major blindspot as I otherwise would have.

Now that I've identified the blindspot, I can work on it, and my social awareness has been increasing at very rapid clip. I had no idea that I had so much potential for social awareness. I had been in a fixed mindset as rather than a growth mindset, I had thought "social skills will never be my strong point, so I shouldn't spend time trying to improve them, instead I should focus on what I'm best at." I'm astonished by how much my relationships have improved over a span of mere weeks.

I give details below.

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Optimizing the Twelve Virtues of Rationality

24 Gleb_Tsipursky 09 June 2015 03:08AM

At the Less Wrong Meetup in Columbus, OH over the last couple of months, we discussed optimizing the Twelve Virtues of Rationality. In doing so, we were inspired by what Eliezer himself said in the essay:

  • Perhaps your conception of rationality is that it is rational to believe the words of the Great Teacher, and the Great Teacher says, “The sky is green,” and you look up at the sky and see blue. If you think: “It may look like the sky is blue, but rationality is to believe the words of the Great Teacher,” you lose a chance to discover your mistake.

So we first decided on the purpose of optimizing, and settled on yielding virtues that would be most impactful and effective for motivating people to become more rational, in other words optimizations that would produce the most utilons and hedons for the purpose of winning. There were a bunch of different suggestions. I tried to apply them to myself over the last few weeks and want to share my findings.

 

First Suggestion

Replace Perfectionism with Improvement

 

Motivation for Replacement

Perfectionism, both in how it pattern matches and in its actual description in the essay, orients toward focusing on defects and errors in oneself. By depicting the self as always flawed, and portraying the aspiring rationalist's job as seeking to find the flaws, the virtue of perfectionism is framed negatively, and is bound to result in negative reinforcement. Finding a flaw feels bad, and in many people that creates ugh fields around actually doing that search, as reported by participants at the Meetup. Instead, a positive framing of this virtue would be Improvement. Then, the aspiring rationalist can feel ok about where s/he is right now, but orient toward improving and growing mentally stronger - Tsuyoku Naritai! All improvement would be about gaining more hedons, and thus use the power of positive reinforcement. Generally, research suggests that positive reinforcement is effective in motivating the repetition of behavior, whereas negative reinforcement works best to stop people from doing a certain behavior. No wonder that Meetup participants reported that Perfectionism was not very effective in motivating them to grow more rational. So to get both more hedons, and thereby more utilons in the sense of the utility of seeking to grow more rational, Improvement might be a better term and virtue than perfectionism.

 

Self-Report

I've been orienting myself toward improvement instead of perfectionism for the last few weeks, and it's been a really noticeable difference. I've become much more motivated to seek ways that I can improve my ability to find the truth. I've been more excited and enthused about finding flaws and errors in myself, because they are now an opportunity to improve and grow stronger, not become less weak and imperfect. It's the same outcome as the virtue of Perfectionism, but deploying the power of positive reinforcement.

 

Second Suggestion

Replace Argument with Community

 

Motivation for Replacement

Argument is an important virtue, and a vital way of getting ourselves to see the truth is to rely on others to help us see the truth through debates, highlight mistaken beliefs, and help update on them, as the virtue describes. Yet orienting toward a rationalist Community has additional benefits besides the benefits of argument, which is only one part of a rationalist Community. Such a community would help provide an external perspective that research suggests would be especially beneficial to pointing out flaws and biases within one's ability to evaluate reality rationally, even without an argument. A community can help provide wise advice on making decisions, and it’s especially beneficial to have a community of diverse and intelligent people of all sorts in order to get the benefits of a wide variety of private information that one can aggregate to help make the best decisions. Moreover, a community can provide systematic ways to improve, through giving each systematic feedback, through compensating for each others' weaknesses in rationality, through learning difficult things together, and other ways of supporting each others' pursuit of ever-greater rationality.  Likewise, a community can collaborate together, with different people fulfilling different functions in supporting all others in growing mentally stronger - not everybody has to be the "hero," after all, and different people can specialize in various tasks related to supporting others growing mentally stronger, gaining comparative advantage as a result. Studies show that social relationships impact us powerfully in numerous ways, contribute to our mental and physical wellbeing, and that we become more like our social network over time (1, 2, 3). This highlights further the benefits of focusing on developing a rationalist-oriented community of diverse people around ourselves to help us grow mentally stronger and get to the correct answer, and gain hedons and utilons alike for the purpose of winning.

 

Self-Report

After I updated my beliefs toward Community from Argument, I've been working more intentionally to create a systematic way for other aspiring rationalists in my LW meetup, and even non-rationalists, to point out my flaws and biases to me. I've noticed that by taking advantage of outside perspectives, I've been able to make quite a bit more headway on uncovering my own false beliefs and biases. I asked friends, both fellow aspiring rationalists and other wise friends not currently in the rationalist movement, to help me by pointing out when my biases might be at play, and they were happy to do so. For example, I tend to have an optimism bias, and I have told people around me to watch for me exhibiting this bias. They pointed out a number of times when this occurred, and I was able to improve gradually my ability to notice and deal with this bias.

 

Third Suggestion

Expand Empiricism to include Experimentation

 

Motivation for Expansion

This would not be a replacement of a virtue, but an expansion of the definition of Empiricism. As currently stated, Empiricism focused on observation and prediction, and implicitly in making beliefs pay rent in anticipated experience. This is a very important virtue, and fundamental to rationality. It can be improved, however, by adding experimentation to the description of empiricism. By experimentation I mean expanding simply observation as described in the essay currently, to include actually running experiments and testing things out in order to update our maps, both about ourselves and in the world around us. This would help us take initiative in gaining data around the world, not simply relying passively on observation of the world around us. My perspective on this topic was further strengthened by this recent discussion post, which caused me to further update my beliefs toward experimentation as a really valuable part of empiricism. Thus, including experimentation as part of empiricism would get us more utilons for getting at the correct answer and winning.

 

Self-Report

I have been running experiments on myself and the world around me long before this discussion took place. The discussion itself helped me connect the benefits of experimentation to the virtue of Empiricism, and also see the gap currently present in that virtue. I strengthened my commitment to experimentation, and have been running more concrete experiments, where I both predict the results in advance in order to make my beliefs pay rent, and then run an experiment to test whether my beliefs actually correlated to the outcome of the experiments. I have been humbled several times and got some great opportunities to update my beliefs by combining prediction of anticipated experience with active experimentation.

 

Conclusion

The Twelve Virtues of Rationality can be optimized to be more effective and impactful for getting at the correct answer and thus winning. There are many way of doing so, but we need to be careful in choosing optimizations that would be most optimal for the most people, as based on the research on how our minds actually work. The suggestions I shared above are just some ways of doing so. What do you think of these suggestions? What are your ideas for optimizing the Twelve Virtues of Rationality?

 

Rationality is about pattern recognition, not reasoning

24 JonahSinick 26 May 2015 07:23PM

Short version (courtesy of Nanashi)

Our brains' pattern recognition capabilities are far stronger than our ability to reason explicitly. Most people can recognize cats across contexts with little mental exertion. By way of contrast, explicitly constructing a formal algorithm that can consistently cats across contexts requires great scientific ability and cognitive exertion.

Very high level epistemic rationality is about retraining one's brain to be able to see patterns in the evidence in the same way that we can see patterns when we observe the world with our eyes. Reasoning plays a role, but a relatively small one. Sufficiently high quality mathematicians don't make their discoveries through reasoning. The mathematical proof is the very last step: you do it to check that your eyes weren't deceiving you, but you know ahead of time that it's your eyes probably weren't deceiving you.

I have a lot of evidence that this way of thinking is how the most effective people think about the world. I would like to share what I learned. I think that what I've learned is something that lots of people are capable of learning, and that learning it would greatly improve people's effectiveness. But communicating the information is very difficult.

It took me 10,000+ hours to learn how to "see" patterns in evidence in the way that I can now. Right now, I don't know how to communicate how to do it succinctly. In order to succeed, I need collaborators who are open to spend a lot of time thinking carefully about the material, to get to the point of being able to teach others. I'd welcome any suggestions for how to find collaborators.

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The Stamp Collector

23 So8res 01 May 2015 11:11PM

I'm writing a series of posts about replacing guilt motivation over on MindingOurWay, and I plan to post the meatier / more substantive posts in that series to LessWrong. This one is an allegory designed to remind people that they are allowed to care about the outer world, that they are not cursed to only ever care about what goes on in their heads.


Once upon a time, a group of naïve philosophers found a robot that collected trinkets. Well, more specifically, the robot seemed to collect stamps: if you presented this robot with a choice between various trinkets, it would always choose the option that led towards it having as many stamps as possible in its inventory. It ignored dice, bottle caps, aluminum cans, sticks, twigs, and so on, except insofar as it predicted they could be traded for stamps in the next turn or two. So, of course, the philosophers started calling it the "stamp collector."

Then, one day, the philosophers discovered computers, and deduced out that the robot was merely a software program running on a processor inside the robot's head. The program was too complicated for them to understand, but they did manage to deduce that the robot only had a few sensors (on its eyes and inside its inventory) that it was using to model the world.

One of the philosophers grew confused, and said, "Hey wait a sec, this thing can't be a stamp collector after all. If the robot is only building a model of the world in its head, then it can't be optimizing for its real inventory, because it has no access to its real inventory. It can only ever act according to a model of the world that it reconstructs inside its head!"

"Ah, yes, I see," another philosopher answered. "We did it a disservice by naming it a stamp collector. The robot does not have true access to the world, obviously, as it is only seeing the world through sensors and building a model in its head. Therefore, it must not actually be maximizing the number of stamps in its inventory. That would be impossible, because its inventory is outside of its head. Rather, it must be maximizing its internal stamp counter inside its head."

So the naïve philosophers nodded, pleased with this, and then they stopped wondering how the stamp collector worked.

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Simultaneous Overconfidence and Underconfidence

20 abramdemski 03 June 2015 09:04PM

Follow-up to this and this on my personal blog. Prep for this meetup. Cross-posted on my blog.

Eliezer talked about cognitive bias, statistical bias, and inductive bias in a series of posts only the first of which made it directly into the LessWrong sequences as currently organized (unless I've missed them!). Inductive bias helps us leap to the right conclusion from the evidence, if it captures good prior assumptions. Statistical bias can be good or bad, depending in part on the bias-variance trade-off. Cognitive bias refers only to obstacles which prevent us from thinking well.

Unfortunately, as we shall see, psychologists can be quite inconsistent about how cognitive bias is defined. This created a paradox in the history of cognitive bias research. One well-researched and highly experimentally validated effect was conservatism, the tendency to give estimates too middling, or probabilities too near 50%. This relates especially to integration of information: when given evidence relating to a situation, people tend not to take it fully into account, as if they are stuck with their prior. Another highly-validated effect was overconfidence, relating especially to calibration: when people give high subjective probabilities like 99%, they are typically wrong with much higher frequency.

In real-life situations, these two contradict: there is no clean distinction between information integration tasks and calibration tasks. A person's subjective probability is always, in some sense, the integration of the information they've been exposed to. In practice, then, when should we expect other people to be under- or over- confident?

Simultaneous Overconfidence and Underconfidence

The conflict was resolved in an excellent paper by Ido Ereve et al which showed that it's the result of how psychologists did their statistics. Essentially, one group of psychologists defined bias one way, and the other defined it another way. The results are not really contradictory; they are measuring different things. In fact, you can find underconfidence or overconfidence in the same data sets by applying the different statistical techniques; it has little or nothing to do with the differences between information integration tasks and probability calibration tasks. Here's my rough drawing of the phenomenon (apologies for my hand-drawn illustrations): 


Overconfidence here refers to probabilities which are more extreme than they should be, here illustrated as being further from 50%. (This baseline makes sense when choosing from two options, but won't always be the right baseline to think about.) Underconfident subjective probabilities are associated with more extreme objective probabilities, which is why the slope tilts up in the figure. Overconfident similarly tilts down, indicating that the subjective probabilities are associated with less-extreme objective probabilities. Unfortunately, if you don't know how the lines are computed, this means less than you might think. Ido Ereve et al show that these two regression lines can be derived from just one data-set. I found the paper easy and fun to read, but I'll explain the phenomenon in a different way here by relating it to the concept of statistical bias and tails coming apart.

The Tails Come Apart

Everyone who has read Why the Tails Come Apart will likely recognize this image:

 

The idea is that even if X and Y are highly correlated, the most extreme X values and the most extreme Y values will differ. I've labelled the difference the "curse" after the optimizer's curse: if you optimize a criteria which is merely correlated with the thing you actually want, you can expect to be disappointed.

 

Applying the idea to calibration, we can say that the most extreme subjective beliefs are almost certainly not the most extreme on the objective scale. That is: a person's most confident beliefs are almost certainly overconfident. A belief is not likely to have worked its way up to the highest peak of confidence by merit alone. It's far more likely that some merit but also some error in reasoning combined to yield high confidence.

In what follows, I'll describe a "soft version" which shows the tails coming apart gradually, rather than only talking about the most extreme points.

Statistical Bias

Statistical bias is defined through the notion of an estimator. We have some quantity we want to know, X, and we use an estimator to guess what it might be. The estimator will be some calculation which gives us our estimate, which I will write as X^. An estimator is derived from noisy information, such as a sample drawn at random from a larger population. The difference between the estimator and the true value, X^-X, would ideally be zero; however, this is unrealistic. We expect estimators to have error, but systematic error is referred to as bias.

Given a particular value for X, the bias is defined as the expected value of X^-X, written EX(X^-X). An unbiased estimator is an estimator such that EX(X^-X)=0 for any value of X we choose.

Due to the bias-variance trade-off, unbiased estimators are not the best way to minimize error in general. However, statisticians still love unbiased estimators. It's a nice property to have, and in situations where it works, it has a more objective feel than estimators which use bias to further reduce error.

Notice, the definition of bias is taking fixed X; that is, it's fixing the quantity which we don't know. Given a fixed X, the unbiased estimator's average value will equal X. This is a picture of bias which can only be evaluated "from the outside"; that is, from a perspective in which we can fix the unknown X.

A more inside-view of statistical estimation is to consider a fixed body of evidence, and make the estimator equal the average unknown. This is exactly inverse to unbiased estimation:

 

In the image, we want to estimate unknown Y from observed X. The two variables are correlated, just like in the earlier "tails come apart" scenario. The average-Y estimator tilts down because good estimates tend to be conservative: because I only have partial information about Y, I want to take into account what I see from X but also pull toward the average value of Y to be safe. On the other hand, unbiased estimators tend to be overconfident: the effect of X is exaggerated. For a fixed Y, the average Y^ is supposed to equal Y. However, for fixed Y, the X we will get will lean toward the mean X (just as for a fixed X, we observed that the average Y leans toward the mean Y). Therefore, in order for Y^ to be high enough, it needs to pull up sharply: middling values of X need to give more extreme Y^ estimates.

If we superimpose this on top of the tails-come-apart image, we see that this is something like a generalization:

 

Wrapping It All Up

The punchline is that these two different regression lines were exactly what yields simultaneous underconfidence and overconfidence. The studies in conservatism were taking the objective probability as the independent variable, and graphing people's subjective probabilities as a function of that. The natural next step is to take the average subjective probability per fixed objective probability. This will tend to show underconfidence due to the statistics of the situation.

The studies on calibration, on the other hand, took the subjective probabilities as the independent variable, graphing average correct as a function of that. This will tend to show overconfidence, even with the same data as shows underconfidence in the other analysis.

 

From an individual's standpoint, the overconfidence is the real phenomenon. Errors in judgement tend to make us overconfident rather than underconfident because errors make the tails come apart so that if you select our most confident beliefs it's a good bet that they have only mediocre support from evidence, even if generally speaking our level of belief is highly correlated with how well-supported a claim is. Due to the way the tails come apart gradually, we can expect that the higher our confidence, the larger the gap between that confidence and the level of factual support for that belief.

This is not a fixed fact of human cognition pre-ordained by statistics, however. It's merely what happens due to random error. Not all studies show systematic overconfidence, and in a given study, not all subjects will display overconfidence. Random errors in judgement will tend to create overconfidence as a result of the statistical phenomena described above, but systematic correction is still an option.

 


I've also written a simple simulation of this. Julia code is here. If you don't have Julia installed or don't want to install it, you can run the code online at JuliaBox.

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