We can judge the direction of sound only because we have two ears. The sound waves reach the right and the left ear with a small time difference because the ears are at slightly different distances from the source of the sound. The eardrums vibrate, and the ear ossicle transmits the impulse to the inner ear. The inner ear sends it further to the brain where the signals from both ears reach at marginally different times. The brain calculates the direction of the sound from the tiny difference in these times.
Without the sense of touch we would be quite helpless. We would not be able to feel one, we would not feel our feet hitting the floor while walking and injuries would go unnoticed because no pain would be felt. We would also be deprived of many pleasant experiences important for social interaction. For blind people the sense of touch is very important. They move around safely by feeling and touching objects in their surroundings. Blind people compensate for their lack of sight by highly developed sense of touch.
We can think of the eye as a kind of camera. The iris behind the cornea is light-sensitive and corresponds to the aperture of the camera. This can be set near or far, depending on the amount of light falling on it. The light rays penetrate the lens of the eye, and fall on the retina. Millions of light-sensitive cells convert the light into signals sent to the brain via the optic nerve. These are put together to make images, and are interpreted by the brain. There are two types of cells in the retina: the light-sensitive rods that help us see in the dark and the less sensitive cones that help us see colours.
Whatever we perceive is not always real. For example, in a magic show, we may think what we see is real, but actually it is an illusion. Even our sense of balance can be deceived, and then one would react with uncertainty and dizziness. Hallucinations often occur because things do not happen the way we expect them to, and the brain gets ‘confused’.
Just as each human being is unique; his grooved fingertips are also unique. Even identical twins do not have the same patterns of grooves on their fingertips. Minor cuts and some skin diseases may cause temporary changes in the patterns, but on healing, the same pattern appears. Since 1901, police have used this knowledge to compare the fingerprints found at a crime site with those of the suspects. In early days, this comparison was done manually and used to be very cumbersome and time-consuming. Today, fingerprints are matched by the computer in a fraction of the time used earlier. 
The skin, as a sense organ, perceives all kinds of touch sensations as signals. These signals are sent to the brain, are interpreted, and the body reacts accordingly. The brain can differentiate between the touch stimuli that we create ourselves and the stimuli given by others. If we try to tickle ourselves, our brain anticipates this type of touch from our hands and prepares itself for it. Since the element of unexpectedness is missing, the body does not respond the same way as it would if someone else were to tickle us.