THE SENSE OF EYE

                      

The most thoroughly studied sensory process is the sense of vision. In visual sensation the light energy (in visible range) enters the eye by passing through cornea, transparent area that allows light to pass into the eye .Then the light energy passes to pupil (the whole center of the iris). When light rays pass through pupil, the muscle called the iris (colored ring) makes the size of the pupil change depending on the amount of light that’s available. You may have noticed this if you have looked at it closely in a mirror. If here is too much light, pupil will shrink to limit the number of light rays that enter. Likewise, if there is very little light available, the pupil will enlarge to let in as many light rays as it can. Just behind the pupil is the lens which focuses the image through a jelly- like substance called the vitreous humor onto the back surface of the eyeball, called the retina. The eye has a complex structure consisting of a transparent lens that focused light on the retina. The retina is covered with two basic types of light-sensitive cells- rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. These cells are located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The point of this connection is called the “blind spot” because it is insensitive to light. Light rays then pass through three layers of neuronal tissue, are transduced into action potentials and are transmitted through the occipital nerve to the visual region of the brain, where hey are registered and interpreted as sights. Many neurons in the visual cortex, called feature detectors, are specialized and are activated only by stimuli of a specific shape or pattern.

The brain combines the input of our two eyes into a single three-dimensional image. In addition, even though the image on the retina is upside-down because of he focusing action of the lens, the brain compensates and provides the right-side-up perception. Experiments have been done with subjects fitted with prisms that invert the images. The subjects go through an initial period of great confusion, but subsequently they perceive the images as right side up.