Artificial Neural Networks

Applied Problems: Image, Sound, and Pattern recognition Decision making  Knowledge discovery  Context-Dependent Analysis  … Artificial Intellect: Who is stronger and why? NEUROINFORMATICS - modern theory about principles and new mathematical models of information processing, which based on the biological prototypes and mechanisms of human brain activities Introduction to Neural Networks 2

Massive parallelism Brain computer as an information or signal processing system, is composed of a large number of a simple processing elements, called neurons. These neurons are interconnected by numerous direct links, which are called connection, and cooperate which other to perform a parallel distributed processing (PDP) in order to soft a desired computation tasks. Connectionism Brain computer is a highly interconnected neurons system in such a way that the state of one neuron affects the potential of the large number of other neurons which are connected according to weights or strength. The key idea of such principle is the functional capacity of biological neural nets determs mostly not so of a single neuron but of its connections Associative distributed memory Storage of information in a brain is supposed to be concentrated in synaptic connections of brain neural network, or more precisely, in the pattern of these connections and strengths (weights) of the synaptic connections. A process of pattern recognition and pattern manipulation is based on: How our brain manipulates with patterns ? Principles of Brain Processing 3

Human brain contains a massively interconnected net of (10 billion) neurons (cortical cells) Biological Neuron - The simple “arithmetic computing” element Brain Computer: What is it? 4

The schematic model of a biological neuron Synapses Dendrites Soma Axon Dendrite from other Axon from other neuron 1.Soma or body cell - is a large, round central body in which almost all the logical functions of the neuron are realized. 2.The axon (output ), is a nerve fibre attached to the soma which can serve as a final output channel of the neuron. An axon is usually highly branched. 3.The dendrites (inputs)- represent a highly branching tree of fibres. These long irregularly shaped nerve fibres (processes) are attached to the soma. 4.Synapses are specialized contacts on a neuron which are the termination points for the axons from other neurons. Biological Neurons 5

? Brain-Like Computer Brain-like computer – is a mathematical model of humane-brain principles of computations. This computer consists of those elements which can be called the biological neuron prototypes, which are interconnected by direct links called connections and which cooperate to perform parallel distributed processing (PDP) in order to solve a desired computational task. Neurons and Neural Net The new paradigm of computing mathematics consists of the combination of such artificial neurons into some artificial neuron net. Artificial Neural Network – Mathematical Paradigms of Brain-Like Computer Brain-like Computer 6

NN as an model of brain-like Computer  An artificial neural network (ANN) is a massively parallel distributed processor that has a natural propensity for storing experimental knowledge and making it available for use. It means that:  Knowledge is acquired by the network through a learning (training) process;  The strength of the interconnections between neurons is implemented by means of the synaptic weights used to store the knowledge. The learning process is a procedure of the adapting the weights with a learning algorithm in order to capture the knowledge. On more mathematically, the aim of the learning process is to map a given relation between inputs and output (outputs) of the network. Brain  The human brain is still not well understood and indeed its behavior is very complex!  There are about 10 billion neurons in the human cortex and 60 trillion synapses of connections  The brain is a highly complex, nonlinear and parallel computer (information-processing system) ANN as a Brain-Like Computer 7

Artificial Intellect with Neural Networks Intelligent Control Technical Diagnistics Intelligent Data Analysis and Signal Processing Intelligent Data Analysis and Signal Processing Advance Robotics Machine Vision Image & Pattern Recognition Intelligent Security Systems Intelligentl Medicine Devices Intelligent Expert Systems Applications of Artificial Neural Networks 8

Image Recognition: Decision Rule and Classifier Is it possible to formulate (and formalize!) the decision rule, using which we can classify or recognize our objects basing on the selected features? Can you propose the rule using which we can definitely decide is it a tiger or a rabbit? 9

Image Recognition: Decision Rule and Classifier Once we know our decision rule, it is not difficult to develop a classifier, which will perform classification/recognition using the selected features and the decision rule. However, if the decision rule can not be formulated and formalized, we should use a classifier, which can develop the rule from the learning process 10

Image Recognition: Decision Rule and Classifier In the most of recognition/classification problems, the formalization of the decision rule is very complicated or impossible at all. A neural network is a tool, which can accumulate knowledge from the learning process. After the learning process, a neural network is able to approximate a function, which is supposed to be our decision rule 11

Why neural network? - unknown multi-factor decision rule Learning process using a representative learning set - a set of weighting vectors is the result of the learning process - a partially defined function, which is an approximation of the decision rule function 12

mpmp m1m1 m2m2 m3m3 xixi yiyi 1. Quantization of pattern space into p decision classes Input Patterns Response: 2. Mathematical model of quantization: “Learning by Examples” Mathematical Interpretation of Classification in Decision Making 13

Data Acquisition Data Analysis Interpretation and Decision Making Signals & parameters Characteristics & Estimations Rules & Knowledge Productions Data Acquisition Data Analysis Decision Making Knowledge Base Adaptive Machine Learning via Neural Network Intelligent Data Analysis in Engineering Experiment 14

Self-organization – basic principle of learning: Structure reconstruction Input Images Teacher Neuroprocessor Responce The learning involves change of structure Learning Rule Learning via Self-Organization Principle 15

Symbol manipulation Pattern recognition Which way of imagination is best for you ?  Dove flies  Lion goes  Tortoise scrawls  Donkey sits  Shark swims Ill-Formalizable Tasks: Sound and Pattern recognition Decision making Knowledge discovery Context-Dependent Analysis What is difference between human brain and traditional computer via specific approaches to solution of ill- formalizing tasks (those tasks that can not be formalized directly)? Symbol Manipulation or Pattern Recognition ? 16

Artificial Neuron  A neuron has a set of n synapses associated to the inputs. Each of them is characterized by a weight.  A signal at the i th input is multiplied (weighted) by the weight  The weighted input signals are summed. Thus, a linear combination of the input signals is obtained. A "free weight" (or bias), which does not correspond to any input, is added to this linear combination and this forms a weighted sum.  A nonlinear activation function φ is applied to the weighted sum. A value of the activation function is the neuron's output. w1w1 wnwn w2w2 x1x1 x2x2 xnxn y 17

A Neuron f is a function to be earned are the inputs φ is the activation function Z is the weighted sum 18

A Neuron Neurons’ functionality is determined by the nature of its activation function, its main properties, its plasticity and flexibility, its ability to approximate a function to be learned 19

Linear activation Threshold activation Hyperbolic tangent activation Logistic activation z z z z Artificial Neuron: Classical Activation Functions 20

Connectionizm NN is a highly interconnected structure in such a way that the state of one neuron affects the potential of the large number of another neurons to which it is connected accordiny to weights of connections Not Programming but Training NN is trained rather than programmed to perform the given task since it is difficult to separate the hardware and software in the structure. We program not solution of tasks but ability of learning to solve the tasks Distributed Memory NN presents an distributed memory so that changing-adaptation of synapse can take place everywhere in the structure of the network. Principles of Neurocomputing 21

Learning and Adaptation NN are capable to adapt themselves (the synapses connections between units) to special environmental conditions by changing their structure or strengths connections. Non-Linear Activation Function Every new states of a neuron is a nonlinear function of the input pattern created by the firing nonlinear activity of the other neurons. Robustness of Assosiativity NN states are characterized by high robustness or insensitivity to noisy and fuzzy of input data owing to use of a highly redundance distributed structure Principles of Neurocomputing 22