Our window into the
large universe has always been a fused two-piece unit called as the eye. The
eye is a complex optical system which collects light from the surrounding
environment, regulates its intensity and focuses it through an adjustable
assembly of lenses to form an image, converts this image into a set of
electrical signals, and transmits these signals to the brain. The new
advancements in the field of biomedical electronics and in the field of
electronics and communication system have changed the perception of eye from an
ordinary sense organ which enables us to see , in to, an organ which generates
trigger pulses to activate and control various electronic devices.
The new methods of
efficient human machine interfaces by using the eye movements and eye blinks are
realized by using a very new bio-electric signal processing technique called as
Electrooculography (EOG). Electrooculography is a technique for measuring the
resting and action potential of the retina. The resulting signal is called the
electrooculogram. Usually, pairs of electrodes are placed either above and
below the eye or to the left and right of the eye. If the eye is moved from the
center position towards one electrode, this electrode "sees" the
positive side of the retina and the opposite electrode "sees" the
negative side of the retina. Consequently, a potential difference occurs
between the electrodes. Assuming that the resting potential is constant, the
recorded potential is a measure for the eye position.
The hardware
components generally required to detect the EOG signals are four to five
electrodes, and the amplifiers and
filters are required for amplification and filtering processes respectively.
The signals are processed using controllers or dsp processors depending up on
the complexity of the application. Some of the important applications of EOG
are in electrooculographic guidance of a wheel chair, retina controlled mouse,
eye controlled switching on and off of electronic and electric devices,
interactive gaming systems etc. The use of EOG for guiding of missiles in the
battle field is a new project under research by the defense systems.
Bioelectricpotentials
refers to the electrical, magnetic or electromagnetic fields produced by living
cells, tissues or organisms. Bioelectric potentials are generated by a variety
of biological processes and generally range in strength from one to a few
hundred millivolts. Biological cells use bioelectricity to store metabolic
energy, to do work or trigger internal changes and to signal one another. Bioelectricity
is the electric current produced by action potentials along with the magnetic
fields they generate through the phenomenon of electromagnetism. Bioelectric
potentials are identical with the potentials produced by devices such as
batteries or generators. In nearly all cases, however, a bioelectric current
consists of a flow of ions (i.e., electrically charged atoms or molecules),
whereas the electric current used for lighting, communication, or power is a
movement of electrons.
If two solutions with different concentrations
of an ion are separated by a membrane that blocks the flow of the ions between
them, the concentration imbalance gives rise to an electric-potential
difference between the solutions. In most solutions, ions of a given electric charge
are accompanied by ions of opposite charge, so that the solution itself has no
net charge. If two solutions of different concentrations are separated by a
membrane that allows one kind of ion to pass but not the other, the
concentrations of the ion that can pass will tend to equalize by diffusion,
producing equal and opposite net charges in the two solutions.
In living cells the
two solutions are those found inside and outside the cell. The cell membrane
separating inside from outside is semi permeable, allowing certain ions to pass
through while blocking others. In particular, nerve- and muscle-cell membranes
are slightly permeable to positive potassium ions, which diffuse outward,
leaving a net negative charge in the cell. The bioelectric potential across a
cell membrane is typically about 50 mill volts; this potential is known as the
resting potential. All cells use their bioelectric potentials to assist or
control metabolic processes, but some cells make specialized use of bioelectric
potentials and currents for distinctive physiological functions, such as the
nerve cell.
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