25-05-2012, 02:15 PM
Biological to Artificial Neuron Model
[attachment=23013]
Martin Gardner in his book titled 'The Annotated Snark" has the following note for the
last illustration sketched by Holiday for Lewis Carroll's nonsense poem 'The Hunting of
the Snark':
"64. Holiday's illustration for this scene, showing the Bellman ringing a knell for the
passing of the Baker, is quite a remarkable puzzle picture. Thousands of readers must
have glanced at this picture without noticing (though they may have shivered with
subliminal perception) the huge, almost transparent head of the Baker, abject terror on his
features, as a gigantic beak (or is it a claw?) seizes his wrist and drags him into the
ultimate darkness."
You also may have not noticed that the face at the first glance, however with a little more
care, you will it easily. As a further note on Martin Gardner's note, we can ask the
question "Is there is any conventional computer at present with the capability of
perceiving both the trees and Baker's transparent head in this picture at the same time?"
Most probably, the answer is no.
Biological Neuron
It is claimed that the human central nervous system is comprised of about 1,3x1010
neurons and that about 1x1010 of them takes place in the brain. At any time, some of
these neurons are firing and the power dissipation due this electrical activity is estimated
to be in the order of 10 watts. Monitoring the activity in the brain has shown that, even
when asleep, 5x107 nerve impulses per second are being relayed back and forth between
the brain and other parts of the body. This rate is increased significantly when awake
[Fischer 1987].
Artificial Neuron Model
As it is mentioned in the previous section, the transmission of a signal from one neuron to
another through synapses is a complex chemical process in which specific transmitter
substances are released from the sending side of the junction. The effect is to raise or
lower the electrical potential inside the body of the receiving cell. If this graded potential
reaches a threshold, the neuron fires. It is this characteristic that the artificial neuron
model proposed by McCulloch and Pitts, [McCulloch and Pitts 1943] attempt to
reproduce. The neuron model shown in Figure 1.6 is the one that widely used in artificial
neural networks with some minor modifications on it.
Network of Neurons
While a single artificial neuron is not able to implement some boolean functions, the
problem is overcome by connecting the outputs of some neurons as input to the others, so
constituting a neural network. Suppose that we have connected many artificial neurons
that we introduced in Section 1.2 to form a network. In such a case, there are several
neurons in the system, so we assign indices to the neurons to discriminate between them.
[attachment=23013]
Martin Gardner in his book titled 'The Annotated Snark" has the following note for the
last illustration sketched by Holiday for Lewis Carroll's nonsense poem 'The Hunting of
the Snark':
"64. Holiday's illustration for this scene, showing the Bellman ringing a knell for the
passing of the Baker, is quite a remarkable puzzle picture. Thousands of readers must
have glanced at this picture without noticing (though they may have shivered with
subliminal perception) the huge, almost transparent head of the Baker, abject terror on his
features, as a gigantic beak (or is it a claw?) seizes his wrist and drags him into the
ultimate darkness."
You also may have not noticed that the face at the first glance, however with a little more
care, you will it easily. As a further note on Martin Gardner's note, we can ask the
question "Is there is any conventional computer at present with the capability of
perceiving both the trees and Baker's transparent head in this picture at the same time?"
Most probably, the answer is no.
Biological Neuron
It is claimed that the human central nervous system is comprised of about 1,3x1010
neurons and that about 1x1010 of them takes place in the brain. At any time, some of
these neurons are firing and the power dissipation due this electrical activity is estimated
to be in the order of 10 watts. Monitoring the activity in the brain has shown that, even
when asleep, 5x107 nerve impulses per second are being relayed back and forth between
the brain and other parts of the body. This rate is increased significantly when awake
[Fischer 1987].
Artificial Neuron Model
As it is mentioned in the previous section, the transmission of a signal from one neuron to
another through synapses is a complex chemical process in which specific transmitter
substances are released from the sending side of the junction. The effect is to raise or
lower the electrical potential inside the body of the receiving cell. If this graded potential
reaches a threshold, the neuron fires. It is this characteristic that the artificial neuron
model proposed by McCulloch and Pitts, [McCulloch and Pitts 1943] attempt to
reproduce. The neuron model shown in Figure 1.6 is the one that widely used in artificial
neural networks with some minor modifications on it.
Network of Neurons
While a single artificial neuron is not able to implement some boolean functions, the
problem is overcome by connecting the outputs of some neurons as input to the others, so
constituting a neural network. Suppose that we have connected many artificial neurons
that we introduced in Section 1.2 to form a network. In such a case, there are several
neurons in the system, so we assign indices to the neurons to discriminate between them.