artificial neural nw - Artificial Neural Networks...

Artificial Neural Networks
- Introduction
Dr. K. Ganesan
Director – TIFAC-CORE in
Automotive Infotronics
VIT University, Vellore – 632 014
[email protected]

Introduction
•
Neural networks are information processing
systems, which are constructed and
implemented to model the human brain .
•
Artificial neural networks perform various
tasks such as pattern-matching and
classification, optimization function,
approximation, vector quantization and data
clustering.
•
These tasks are difficult for traditional
computers, which are faster in algorithmic
computational tasks and precise arithmetic
operations.

Artificial Neural Network
•
ANNs possess large number of highly interconnected
processing elements called nodes or units or neurons , which
usually operate in parallel and are configured in specific
architectures.
•
Each neuron is connected with the other by a connection link .
•
Each connection link is associated with weights which contain
information about the input signal .
•
ANNs collective behavior is characterized by their ability to
learn, recall and generalize training patterns.
•
Each neuron has an internal state of its own.
•
The internal state is called the activation or activity level of
neuron, which is the function of the inputs the neurons receives.
•
Activation of a neuron is transmitted to other neurons .
•
A neuron can send only one signal at a time , which can be
transmitted to several other neurons.

Biological Neural Network
The human brain consists of about 10^11 neurons.
The structure of neuron is as shown below:

The biological neurons has 3
important parts:
•
Soma or cell body – where cell nucleus is located (cpu).
•
Dendrites – where the nerve is connected to the cell body
(inputs).
•
Axon – carries the impulses of the neuron (cables).
•
Dendrites are tree like networks made of nerve fiber
connected to the cell body.
•
An axon is a single, long connection extending from the cell
body and carrying signals from the neuron.
•
The end of the axon splits into fine strands .
•
Each strand terminates into a small bulb-like organ called
synapse.
•
Through synapse the neuron introduces its signals to other
nearby neurons (gateways).
•
There are about 10^4 synapses per neuron in the human brain.

Refractory period
•
Electric impulses are passed between the synapse and the
dendrites.
•
Here signal transmission involves a chemical process in which
specific transmitter substances are released from the sending side of
the junction.
•
This results in increase or decrease in the electric potential inside the
body of the receiving cell.
•
If the electric potential reaches a threshold then the receiving cell
fires and a pulse or action potential of fixed strength and duration
is sent out through the axon to the synaptic junctions of the other
cells.