2,983 research outputs found
On palimpsests in neural memory: an information theory viewpoint
The finite capacity of neural memory and the
reconsolidation phenomenon suggest it is important to be able
to update stored information as in a palimpsest, where new
information overwrites old information. Moreover, changing
information in memory is metabolically costly. In this paper, we
suggest that information-theoretic approaches may inform the
fundamental limits in constructing such a memory system. In
particular, we define malleable coding, that considers not only
representation length but also ease of representation update,
thereby encouraging some form of recycling to convert an old
codeword into a new one. Malleability cost is the difficulty of
synchronizing compressed versions, and malleable codes are of
particular interest when representing information and modifying
the representation are both expensive. We examine the tradeoff
between compression efficiency and malleability cost, under a
malleability metric defined with respect to a string edit distance.
This introduces a metric topology to the compressed domain. We
characterize the exact set of achievable rates and malleability as
the solution of a subgraph isomorphism problem. This is all done
within the optimization approach to biology framework.Accepted manuscrip
von Neumann-Morgenstern and Savage Theorems for Causal Decision Making
Causal thinking and decision making under uncertainty are fundamental aspects
of intelligent reasoning. Decision making under uncertainty has been well
studied when information is considered at the associative (probabilistic)
level. The classical Theorems of von Neumann-Morgenstern and Savage provide a
formal criterion for rational choice using purely associative information.
Causal inference often yields uncertainty about the exact causal structure, so
we consider what kinds of decisions are possible in those conditions. In this
work, we consider decision problems in which available actions and consequences
are causally connected. After recalling a previous causal decision making
result, which relies on a known causal model, we consider the case in which the
causal mechanism that controls some environment is unknown to a rational
decision maker. In this setting we state and prove a causal version of Savage's
Theorem, which we then use to develop a notion of causal games with its
respective causal Nash equilibrium. These results highlight the importance of
causal models in decision making and the variety of potential applications.Comment: Submitted to Journal of Causal Inferenc
Towards hypergraph cognitive networks as feature-rich models of knowledge
Semantic networks provide a useful tool to understand how related concepts
are retrieved from memory. However, most current network approaches use
pairwise links to represent memory recall patterns. Pairwise connections
neglect higher-order associations, i.e. relationships between more than two
concepts at a time. These higher-order interactions might covariate with (and
thus contain information about) how similar concepts are along psycholinguistic
dimensions like arousal, valence, familiarity, gender and others. We overcome
these limits by introducing feature-rich cognitive hypergraphs as quantitative
models of human memory where: (i) concepts recalled together can all engage in
hyperlinks involving also more than two concepts at once (cognitive hypergraph
aspect), and (ii) each concept is endowed with a vector of psycholinguistic
features (feature-rich aspect). We build hypergraphs from word association data
and use evaluation methods from machine learning features to predict concept
concreteness. Since concepts with similar concreteness tend to cluster together
in human memory, we expect to be able to leverage this structure. Using word
association data from the Small World of Words dataset, we compared a pairwise
network and a hypergraph with N=3586 concepts/nodes. Interpretable artificial
intelligence models trained on (1) psycholinguistic features only, (2)
pairwise-based feature aggregations, and on (3) hypergraph-based aggregations
show significant differences between pairwise and hypergraph links.
Specifically, our results show that higher-order and feature-rich hypergraph
models contain richer information than pairwise networks leading to improved
prediction of word concreteness. The relation with previous studies about
conceptual clustering and compartmentalisation in associative knowledge and
human memory are discussed
The Performance of Associative Memory Models with Biologically Inspired Connectivity
This thesis is concerned with one important question in artificial neural networks, that is, how biologically inspired connectivity of a network affects its associative memory performance.
In recent years, research on the mammalian cerebral cortex, which has the main
responsibility for the associative memory function in the brains, suggests that
the connectivity of this cortical network is far from fully connected, which is
commonly assumed in traditional associative memory models. It is found to
be a sparse network with interesting connectivity characteristics such as the
āsmall world networkā characteristics, represented by short Mean Path Length,
high Clustering Coefficient, and high Global and Local Efficiency. Most of the networks in this thesis are therefore sparsely connected.
There is, however, no conclusive evidence of how these different connectivity
characteristics affect the associative memory performance of a network. This
thesis addresses this question using networks with different types of
connectivity, which are inspired from biological evidences.
The findings of this programme are unexpected and important. Results show
that the performance of a non-spiking associative memory model is found to be
predicted by its linear correlation with the Clustering Coefficient of the network,
regardless of the detailed connectivity patterns. This is particularly important
because the Clustering Coefficient is a static measure of one aspect of
connectivity, whilst the associative memory performance reflects the result of a
complex dynamic process.
On the other hand, this research reveals that improvements in the performance
of a network do not necessarily directly rely on an increase in the networkās
wiring cost. Therefore it is possible to construct networks with high
associative memory performance but relatively low wiring cost. Particularly,
Gaussian distributed connectivity in a network is found to achieve the best
performance with the lowest wiring cost, in all examined connectivity models.
Our results from this programme also suggest that a modular network with an
appropriate configuration of Gaussian distributed connectivity, both internal to
each module and across modules, can perform nearly as well as the Gaussian
distributed non-modular network.
Finally, a comparison between non-spiking and spiking associative memory
models suggests that in terms of associative memory performance, the
implication of connectivity seems to transcend the details of the actual neural
models, that is, whether they are spiking or non-spiking neurons
Parallel Architectures for Planetary Exploration Requirements (PAPER)
The Parallel Architectures for Planetary Exploration Requirements (PAPER) project is essentially research oriented towards technology insertion issues for NASA's unmanned planetary probes. It was initiated to complement and augment the long-term efforts for space exploration with particular reference to NASA/LaRC's (NASA Langley Research Center) research needs for planetary exploration missions of the mid and late 1990s. The requirements for space missions as given in the somewhat dated Advanced Information Processing Systems (AIPS) requirements document are contrasted with the new requirements from JPL/Caltech involving sensor data capture and scene analysis. It is shown that more stringent requirements have arisen as a result of technological advancements. Two possible architectures, the AIPS Proof of Concept (POC) configuration and the MAX Fault-tolerant dataflow multiprocessor, were evaluated. The main observation was that the AIPS design is biased towards fault tolerance and may not be an ideal architecture for planetary and deep space probes due to high cost and complexity. The MAX concepts appears to be a promising candidate, except that more detailed information is required. The feasibility for adding neural computation capability to this architecture needs to be studied. Key impact issues for architectural design of computing systems meant for planetary missions were also identified
Generation of folk song melodies using Bayes transforms
The paper introduces the `Bayes transform', a mathematical procedure for putting data into a hierarchical representation. Applicable to any type of data, the procedure yields interesting results when applied to sequences. In this case, the representation obtained implicitly models the repetition hierarchy of the source. There are then natural applications to music. Derivation of Bayes transforms can be the means of determining the repetition hierarchy of note sequences (melodies) in an empirical and domain-general way. The paper investigates application of this approach to Folk Song, examining the results that can be obtained by treating such transforms as generative models
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