The Plan The article How does this thing work ? Discussion
A Large-scale Model of the Functioning Brain
Seminar presentation
Ardi Tampuu
February
The Plan The article How does this thing work ? Discussion
What's going to happen today ?
Today's presentation will consist roughly in 3 parts :
Description of the behaviour and capacities of the model
General introduction to the methods applied
Discussion about this type of models
The Plan The article How does this thing work ? Discussion
A large scale model of the functioning Brain
The model presented in this article is called "Semantic PointerArchitecture Uni�ed Network" (SPAUN).
2.5 million neurons
20 brain structures and the functional connectivity betweenthem
Input 28X28 pixels results in behavioural output of moving arobotic arm
Solves 8 di�erent tasks, for which it needs memory,contingency detection, reasoning
The Plan The article How does this thing work ? Discussion
The diversity of tasks
The 8 tasks are :A0 : copy drawing (needs extraction of details from images)
A1 : image recognition (extracting a concept from an image)- 94%
A2 : reinforcement learning (needs modi�cation of connection weights)
A3 : remember sequences (needs memorizing long sequences)
A4 : counting (adding two numbers) - 400ms per position counted
A5 : P and K questions (extracting information from a sequence)
A6 : rapid variable creation (�nding regularities)
A7 : �uid reasoning (determining the operator/transformation to be applied) -88%
The Plan The article How does this thing work ? Discussion
The connectivity
The Plan The article How does this thing work ? Discussion
The functional organization
The Plan The article How does this thing work ? Discussion
Results and predictions
Accurate copy drawing (A0) and e�cient RL (A2)
The Plan The article How does this thing work ? Discussion
Results and predictions
The model uses serial WM and predicts how correlations in �ringpatterns decrease when more items are added :
The Plan The article How does this thing work ? Discussion
Results and predictions
In A4(counting), reaction times are similar to human behaviour.In A5 we see the e�ects of primacy and recency.
The Plan The article How does this thing work ? Discussion
Yeah, cool, but how does it work ?
The Plan The article How does this thing work ? Discussion
The basic concepts
The model is based on NEF(representations, transformations) andSPA (linking areas with each other).
The Plan The article How does this thing work ? Discussion
The basic concepts
The �ring pattern in working memory is a function of all of itsinputs. The resulting �ring pattern can later be decoded from thememory.
MemoryTrace = Position1⊗ Item1+ Position2⊗ Item2+ ...where :
Position1 = Base
Position2 = Position1⊗ Base
and
One = Base
Two = One ⊗ AddOne
The Plan The article How does this thing work ? Discussion
How does the system learn to do this ?
Actual learning only takes place in RL task. In other cases networkconnectivity does not change during tasks, only the state of thesystem does.
Learning during RL does not in�uence the performance in othertasks.
The Plan The article How does this thing work ? Discussion
How does the system learn to do this ?
It seems an instance of Spaun is tuned beforehand to bestsegregate between di�erent states and di�erent inputs.
Visual system is trained using RBM, not spiking neurons
Are sub-systems taught one by one or all together ?
What types of neural networks and learning rules are applied ?
Source code is accessible
The Plan The article How does this thing work ? Discussion
Working memory
The serial memorizing of inputs in the WM is illustrated below :
The Plan The article How does this thing work ? Discussion
Restricted Boltzmann Machine
The visual system uses a type of Restriced Boltzmann Machine :
Named after the Boltzmann Distribution of probabilities
Layered structure with visible and hidden units, no recurrentconnections
Hidden units can be seen as detecting patterns in the activityof VU
Activity of the hidden units can be used as input to anotherlayer of RBM
The Plan The article How does this thing work ? Discussion
Can we trust these guys ?
Is Spaun an "arti�cial intelligence" or is it simply a cleverlydesigned computer program ?
+ can switch between tasks by itself
+ does not respond to falsely posed questions
+ can be adapted to solve di�erent tasks
+ involves spiking neurons with randomized parameters
− is limited to using numbers from 0 to 9
− not capable of learning completely new tasks
− in NEF connection weights are de�ned mathematically, not byRL or spike-based rules
The Plan The article How does this thing work ? Discussion
Everything that glitters is not gold ?
Sophisticated models often make you believe they a very close tosolving the "big questions".
nobody wants to discuss the limitations of their work
it's more interesting to discuss the parts the model learned byitself rather than what was hard-coded to the system
why is the training procedure or the "life-cycle" of Spaun notdescribed ?
The Plan The article How does this thing work ? Discussion
Are such models reproducible ?
The article and the SI are not su�cient to reproduce the model,but source code is provided.
it is very hard to explain complex algorithms in a few words inthe article
most readers are not interested in details
no standards exist for model description
The Plan The article How does this thing work ? Discussion
Other models
Brain-like systems capable of learning complex behaviour are verymuch in fashion :
DeepMind model learning to play computer games(http ://arxiv.org/pdf/1312.5602v1.pdf)
Mostly adaptations of RBM are used, not biologically precise