SEEING AND HEARING AND THEIR PERCEPTION

SIGHT

Without a doubt, the two ‘eyes’ along with the brain in our body, enables us to see the beautiful world around us. The images that we see are made up of the light reflected from the objects we look at. This light travel in a straight line into the eye through the cornea (the clear, dome-shaped surface that covers the front of the eye). The cornea bends, or refracts, this incoming light. The iris (the colored part of the eye) regulates the size of the pupil, the opening that controls the amount of light that enters the eye. Behind the pupil is the lens (a clear part of the eye that further focuses light, or an image, onto the retina). The retina is a thin, delicate, photosensitive tissue that contains the special ‘photoreceptor’ cells that convert light into electrical signals. These electrical signals are processed further, and then travel from retina of the eye to the brain through the optic nerve, a bundle of about one million nerve fibers. The brain makes sense of the signals and tells us what we are seeing. Our eyes collect visual information and begin this complex process. If a bright red beach ball comes whirling towards you, you see its color, shape, and motion- all at once, but your brain deals with each of these separately.

HEARING

Hearing is one of the five senses. It is a complex process of picking up sound attaching meaning to it. The ability to hear is critical to understanding the world around us. The human ear is a fully developed part of our body at birth and responds to sounds that are very faint as well as sounds that are very loud. Even before birth, infants respond to sound. The ear can be divided into three parts, leading up to the brain: the outer ear, the middle ear, and the inner ear. The outer ear consists of the ear canal and eardrum. Sound travels down the ear canal, striking the eardrum and causing it to move or vibrate. The middle ear is a space behind the eardrum that contains three small bones called ossicles. This chain of tiny bones is connected to the eardrum at one end and to an opening to the inner ear at the other end. Vibrations from the eardrum cause the ossicles to vibrate which, in turn, creates movement of the fluid in the inner ear. Movement of the fluid in the inner ear, or cochlea, causes changes in tiny structures called hair cells. This movement of the hair cells sends electric signals from the inner ear up the auditory nerve to the brain. The brain then interprets these electrical signals as sound.