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Home->Computation


Computation


A neural network is made up of synchronous, communicating neurons. These neural elements can be abstracted using Turing's automata. Computation of information is a dynamic, time dependent process. The neural machines must pass state information embedded in the temporal code from one automaton to the next. The temporal code resides in the frequency and duration of the synapses, and these synapses occur in waves across the layers of neurons.


To really understand how neural computation occurs, we must study the essential components that make up our neural model. The neural model of computation is based on how we intuitively think the brain processes information. However, we don't know how close we are to actually realizing how the brain's neurons generates the information as a global network that make up our consciousness or awareness.

To build a neural network I use to think that you create the standard neural layers, and propagate a synaptic wave of synapses through these layers. You let the neural network determine how information is formed or created through the neural layers by letting the neurons in these layers generate synchronous fire paths. But of course, I now know and really appreciate now, that this is a simplistic view. In building recurrent networks for example, I had failed to think enough about how I was losing state information using weight matrices. The weight matrices did not contain enough details for them to describe the evolution of each state as a function of time, so I was losing information as I let the state propagate in time. Using weight matrices were fine in describing patterns that do not change in time, but was a stone mountain blocking any development in understanding dynamic patterns. Using weight matrices in the standard recurrent neural networks destroys state information which is "of the essence" in automata theory.

I remember reading articles that said recurrent neural networks were Turing complete. It's easy to say yes to this in theory, but not in practice. Recurrent neural networks in the 1980s were built using weight matrices. All the great feed-forward, recurrent multi-layered networks used weight matrices. The initial success of these networks in the early 1980s from applications in visual pattern recognition had led the amiable Tom J. Schwarz to write in Time magazine that "Neural networks are going to be the steam engines of the 21st century." But the old recurrent network software in practice were not Turing complete.

I abandoned development using matrix driven networks after 2001, quite awhile ago now. The basic I/O model of the "black box" matrix is not appropriate for modelling neurons in chains or circuits. The most outstanding behavior of neurons is how they synchronize themselves together inside of parallel circuits. The matrix model does not intrinsically allow you to capture this effect. But I have not been able to eliminate using matrix methods from my software toolbox because they are so powerful in doing pattern recognition for static, time-independent processes. And I think, since this computational technique is so efficient, that the brain must use some form of global array association for most image recognition problems.

A very successful state processor used in speech recognition for example executes the hidden Markov model algorithm. Markov chains depend on the state information from each previous time sample. The Markov chains I use now are embedded with the wave packet description of the synapse. For me, the wave packet model is more intuitive to use then the first-order hidden Markov model.

The model I've continue to build upon is a combination of Turing's computational automata using communicating state machine executing sychronously and the wave packet model used in signal processing application. I think of synthetic neurons as gates which pass information in a time sensitive way. The gate functions because each neuron, from self training, has developed a history of learning from the network. The training process is limited by the amount of information available to the neuron. Furthermore, the ability of neural circuits to transfer this information in spike trains is limited by the uncertainty principle [1].

I now use wave theory to describe the neural field as an ensemble. There is a limit to the amount of information contained in each synapse which can be transferred from neuron to neuron in neural circuits. This limitation exists because you can only measure energy to an certain finite accuracy within a finite time period. The best dynamic, time-dependent description of energy or information we can write for a single synapse or a spike-train is using a wave packet [2]. I'm not saying a wave packet contains all the information in a synapsing neuron that neuro-biologists [3] would envision, but that the description of the form [4] of the energy produced by the neuron is innately limited.


Computation With Binary Trees

I feel like I should mention some form of concrete computational algorithm as in computing using the binary tree. The temporal synapses within a spike train produced by a neuron contains an ordered sequence of spikes. Within this sequence is the computational structure which the neuron operates with. The generation of spikes within a spike train can be formulated by ordering the synapses using a binary tree.

A measure of synchronization which physical waves like sound waves possess is in its similarity. Two wave packets, representing spike train signals, which are similar in temporal duration and frequency spectrum naturally resonate which each other according to the superposition principle of wave mechanics. The similarity or correlation of two wave packets can also be measured in the "algorithms" by the similarity in its ordered sequence or binary tree structure.


References


1. The Limits of Information, Glenn Takanishi, Nov. 2010

2. The Gabor, wave packet, transform helps to extract parts of a signal using a Gaussian function. You can make a collection of signal attributes by superimposing the Gaussian function over the targeted signal function. Then you can put this collection of little signals or wave packets in a dictionary for lookup during pattern recognition. Mathematically, this is called taking the convolution of the template Gaussian function with the sampled signal.

3. In 1999, I attended a course on the software program Neuron given by Professors Carnevale and Hines. Most of the technical biology never sank into my head, but I really appreciated the spirit of the course and congeniality of the teachers.

4. The term form is generally used to mean shape. This term, along with structure, is also used in ancient philosophy to connotate an object's essential "being". In the case of a neural spike train or signal, the information contained in the synapses which is transmitted to other neurons reside in the duration or width of the synapses. You can also think of it this way: that the information in a neuron is in its chirp or musical intonation. The information in a cluster of neural circuits lies in the musical score written on the sheet music of the orchestra. Thinking of neurons working together synchronously places less emphasis on the importance of when each individual neuron starts a synaptic wave train, and more significance on neurons working continuously for long periods together. Group of neurons in large synchronous circuits can process sensory data more accurately as a function of time. The control our muscles to get temporally significant responses down in the milli-second range, for example, depends upon neurons working together in a group.


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