1 1 Introduction

1 2 Course Objectives This course gives an introduction to basic neural network architectures and learning rules. Emphasis is placed on the mathematical analysis of these networks, on methods of training them and on their application to practical engineering problems in such areas as pattern recognition, signal processing and control systems.

1 3 What Will Not Be Covered Review of all architectures and learning rules Implementation –VLSI –Optical –Parallel Computers Biology Psychology

1 4 Historical Sketch Pre-1940: von Hemholtz, Mach, Pavlov, etc. –General theories of learning, vision, conditioning –No specific mathematical models of neuron operation 1940s: Hebb, McCulloch and Pitts –Mechanism for learning in biological neurons –Neural-like networks can compute any arithmetic function 1950s: Rosenblatt, Widrow and Hoff –First practical networks and learning rules 1960s: Minsky and Papert –Demonstrated limitations of existing neural networks, new learning algorithms are not forthcoming, some research suspended 1970s: Amari, Anderson, Fukushima, Grossberg, Kohonen –Progress continues, although at a slower pace 1980s: Grossberg, Hopfield, Kohonen, Rumelhart, etc. –Important new developments cause a resurgence in the field

1 5 What is artificial neural networks? Is there really a definition for it? Do we need a definition? Different people may define it differently, we will leave this to the reader, students, to define it as their initial understanding of the subject is. We later go back to it and see if can define it based on what we have learned in the course. This is one of the most common definition for NN: A NN is a network of many simple processors (“units”), each possibly having a small amount of local memory. The units are connected by communication channels (“connections”) which usually carry numeric (as opposed to symbolic) data, encoded by any of various means. Each unit operates on its local data and on the inputs that its receives via the connections.

1 6 Applications Aerospace –High performance aircraft autopilots, flight path simulations, aircraft control systems, autopilot enhancements, aircraft component simulations, aircraft component fault detectors Automotive –Automobile automatic guidance systems, warranty activity analyzers Banking –Check and other document readers, credit application evaluators Defense –Weapon steering, target tracking, object discrimination, facial recognition, new kinds of sensors, sonar, radar and image signal processing including data compression, feature extraction and noise suppression, signal/image identification Electronics –Code sequence prediction, integrated circuit chip layout, process control, chip failure analysis, machine vision, voice synthesis, nonlinear modeling

1 7 Applications Financial –Real estate appraisal, loan advisor, mortgage screening, corporate bond rating, credit line use analysis, portfolio trading program, corporate financial analysis, currency price prediction Manufacturing –Manufacturing process control, product design and analysis, process and machine diagnosis, real-time particle identification, visual quality inspection systems, beer testing, welding quality analysis, paper quality prediction, computer chip quality analysis, analysis of grinding operations, chemical product design analysis, machine maintenance analysis, project bidding, planning and management, dynamic modeling of chemical process systems Medical –Breast cancer cell analysis, EEG and ECG analysis, prosthesis design, optimization of transplant times, hospital expense reduction, hospital quality improvement, emergency room test advisement

1 8 Applications Robotics –Trajectory control, forklift robot, manipulator controllers, vision systems Speech –Speech recognition, speech compression, vowel classification, text to speech synthesis Securities –Market analysis, automatic bond rating, stock trading advisory systems Telecommunications –Image and data compression, automated information services, real-time translation of spoken language, customer payment processing systems Transportation –Truck brake diagnosis systems, vehicle scheduling, routing systems

1 9 Neural Network Models Neural networks have been used to model the human vision system. Neural networks learn by experience, generalize from previous experiences to new ones, and can make decisions. The human nervous system consists of cells called neurons. There are hundreds of billions of neurons, each connected to hundreds or thousands of other neurons. Each neuron receives, processes, and transmits electro-chemical signals over the neural pathways that make up the brain’s communication system. Neural network models consist of a large number of neurons or simple processing units, also referred to as neurodes.

Neural Network Models An artificial neuron mimics the characteristics of the biological neuron. A set of inputs are applied, each representing an output of another neuron. Each input is multiplied by a corresponding weight, analogous to synaptic strengths. The weighted inputs are summed to determine the activation level of the neuron. The connection strengths or the weights represent the knowledge in the system. Information processing takes place through the interaction among these units.

1 1 Biology Neurons respond slowly – s compared to s for electrical circuits The brain uses massively parallel computation –  neurons in the brain –  10 4 connections per neuron

Neuron Representations Axon Cell body Dendrites Synapse (interconnection) Biological Neuron Representation x1x1 x2x2 x3x3 F Out=F(net+ ) Artificial Neuron Representation Synapse are elementary signal processing devices. It is a biochemical device that converts a pre-synaptic electrical signal into a chemical signal and then back into a post-synaptic electric signal. The input pulse train has its amplitude modified by parameters stored in the synapse. Depending on the type of the synapse the nature of this modification varies. It can be inhibitory or excitatory.

Neuron Representations Biological neurons are the basic building blocks of the brain. The neurons operate in milliseconds which is about 6 times slower than silicon logic gates. Brain is very energy efficient. It consumes only about Joules operation/sec. A digital computer takes J/opr-sec. The postsynaptic signals are aggregated and transferred to the nerve cell body via dendrites.

Neuron Representations The cell body generates the output neuronal signal, that will be in the form of spikes and will be transferred to the synaptic terminals of other neurons via axon. The synaptic parameters (weights) controls the frequency of firing of a neuron based on the total synaptic activities. The pyramidal cell can receive 10 4 synaptic inputs and can fan-out the output signal to thousands of target cells. About 1 million synapses are formed per second at the early stage of human brain developments (age 0-2). Synapses are then modified through the learning process.