Question

in a detailed paragraph since any receptor can respond to any visible wavelength, how can visual systems identify different wavelenghts?

Answer 1

HUMAN EYE CAN RECOGNIZE ABOUT 150 DIFFERENT COLOURS IN THE VISIBLE SPECTRUM. DISCRIMINATION AND APPRECIATION OF COLOURS DEPEND UPON THE ABILITY OF RECEPTORS IN THE RETINA.

WAVELENGTH IS THE DISTANCE BETWEEN TWO IDENTICAL POINTS IN THE WAVE OF LIGHT ENERGY. ACCORDINGLY, RED HAS GOT THE MAXIMUM WAVELENTH AND VIOLET HAS GOT THE MINIMUM WAVELENTH. IN THE SPECTRUM CLOURS OCCUPY THE POSITION ACCORDING TO THEIR WAVELENTHS.

MANY THEORIES ARE AVAILABLE TO EXPLAIN THE MECHANISM OF PRECEPTION OF COLOUR BY EYES. FOLLOWING ARE THE THEORIES WHICH ARE WIDELY ACCEPTED:

1.THOMAS YOUNG TRICHROMATIC THEORY

ACCORDING TO THOMAS YOUNG , RETINA HAS THREE TYPES OF CONES. EACH ONE POSSES ITS OWN PHTOSENSITIVE SUBSTANCE. EACH CONE GIVES RESPONSE TO ONE OF THE PRINARY COLOURS.- RED ,GREEN AND BLUE. DIFFERENT COLOUR SENSATIONS ARE PRODUCED BY THE STIMULATION OF VARIOUS COMBINATION OF THESE THREE TYPES OF CONES FOR SENSATION OF WHITE LIGHT , ALL THREE TYPES OF CONES ARE STIMULATED EQUALLY.

2.HELMHOLTZ TRICHROMATIC THEORY

HELMHOLTZ SUBSTITUTED THE SENSITIVE FILAMENTS OF OPTIC NERVE FOR CONES. THE SENSITIVE FILAMENTS OF NERVES GIVE RESPONSE SELECTIVITY TO ONE OR OTHER OF THE THREE PRIMARY COLOURS. IT IS ALSO CALLED YOUNG - HELMHOLTZ THEORY.

3.GRANIT DOMINATOR-MODULATOR THEORY

GRANIT OBSERVED THAT THE GANGLIONIC CELLS OF RETINA ARE STIMULATED BY THE WHOLE OF THE VISUAL SPECTRUM. HE STUDIED THE ACTION POTENTIALS IN GANGLIONIC CELLS, WHICH ARE STIMULATED BY LIGHT AND OBTAINED SOME SENSITIVITY CURVES. SENSITIVITY CURVES WERE RECORDED BY USING DIFFERENT WAVELENTHS OF LIGHT BOTH IN LIGHT-ADAPTED AND DARK- ADAPTED EYES. ON THE BASIS OF THESE SENSITIVITY CURVES , GRANIT CLASSIFIED THE GANGLIONIC CELLS IN TO TWO GROUPS NAMELY , DOMINATORS AND MODULATORS.

DOMINATORS:

DOMINATORS ARE RESPONSIBLE FOR BRIGHTNESS OF LIGHT. DOMINATORS ARE FURTHER DIVIDED AS DOMINATORS FOR CONES AND DOMINATORS FOR RODS

DOMINATORS FOR CONES- DOMINTORS FOR CONES RESPOND IN LIGHT ADAPTED EYE AND BROAD SENSITIVITY CURVE IS PRODUCED WTH A MAXIMUM RESPONSE AROUD THE WAVELENTH OF

55 ANGSTROM.

DOMINATORS FOR RODS- IT RESPOND IN DARK ADAPTED EYE AND IN THE SENSITIVITY CURVE THE MAXIMUMRESPONSE IS GIVEN AT THE WAVELENGTH OF 500 ANGSTROM.

MODULATORS:

MODULATORS ARE RESPONSIBLE FOR DIFFERENT COLOUR SENSATIONS. MODULATORS ARE OF THREE TYPES:

MODULATORS OF BLUE- STIMULATED BY LIGHT OF WAVELENGTH OF 450 TO 470 ANGSTROM

MODULATORS OF GREEN-STIMULATED BY LIGHT OF WAVWLENTHS 520 TO 540 ANGSTROM

MODULATORS OF RED-YELLOW-STIMULATED BY LIGHT OF WAVELNENGTHS OF 580 TO 600 ANGSTROM.

IF GREEN LIGHT FALLS ON RETINA, MODULATORS OF GREEN ARE STIMULATED AND OTHER TWO ARE LESS AFFECTED. THUS ACCORDING TO GRANIT THE DOMINATORS ARE RESPONSIBLE FOR BRIGHTNESS OR INTENSITY OF LIGHT, BOTH IN DARK -ADAPTED (RODES) AND LIGHT- ADAPTED ( CONES) EYES.THE MODULATORS ARE RESPONSIBLE FOR COLOUR VISION IN LIGHT- ADAPTED EYES.

4. HARTRIDGE POLYCHROMATIC THEORY:

ACCORDING TO THIS THEORY , HUMAN RETINA HAS SEVEN TYPES OF RECEPTORS . ALL THE SEVEN RECEPTORS ARE DIVIDED IN TO THREE UNITS.

FIRST UNIT-

FIRST UNIT IS A TRICOLOUR UNIT CONSISTING OF RECEPTORS FOR ORANGE ,GREEN AND BLUE.

SECOND UNIT-

SECOND UNIT IS DICOLOUR UNIT WITH RECEPTORS FOR YELLOW AND BLUE COLOURS . RECEPTORS FOR YELLOW AND BLUE ARE COMPLEMENTARY TO EACH OTHER.

THIRD UNIT-

THIRD UNIT IS ANOTHER DICOLOUR UNIT WITH RED AND BLUE- GREEN RRECEPTORS