Question

Describe the physiological mechanisms necessary for the individual to SENSE a photon of blue light (around wavelength 475) AND describe the mechanisms necessary for an individual to PERCEIVE an object as the color blue.

Answer 1

Colour sense is one type of ability of human brain and eye to discriminate between different colours of different wavelength. Colour vision is the main functions of the cone cells in the retina. This is also called photopic vision. From the childhood people are taught names for their different colour sensation and then they use these names whenever the same sensation is perceived.

SENSE of a photon of blue light: Young-Helmholtz shows that in reality there are only 3 major colours are present (Red, green and blue). They are called primary colour. Blue colour light is sensed by the blue sensitive cone pigment in the cone cell . These cone cells are named as cyanolabe. This pigment absorbs the blue colour with a peak at 440 nm wavelength. Blue light of 492-450 nm bandwidth are absorbed by this cone cell. So in this way the blue light (around wavelength 475) are sensed by the specific cone cell.

PERCEIVE of an object as the color blue: An individual sense an object as blue colour in the blue sensitive cone pigment in the cone cell, after that the sensation is carried by optic nerve to optic tract via optic chiasma. After leaving optic tract the sensation will go to the parvocellular portion of the lateral geniculate body (LGB), from the LGB the colour information relayed to the striate cortex (area 17). From this region the signal goes to blobs in the layer II and III. From this region of the brain the signal travels to the visual association area and ultimately to lingual and fusiform gyri of occipital lobe (Visual cortex). In this lingual and fusiform gyri of occipital lobe the colour of the object (blue) is perceived. After recalling of past memory of blue colour sensation of the individual, he/she can identify the blue colour of the object.