Sensation is the process by which one form of energy is converted into another form. For example light is converted into neural impulses by which we code sensory events in our system that can be processed by our brain. The sensory systems process information reaching to the brain. The motor systems process information going out of the brain to muscles and glands.

Sometimes, parents switch on the T.V. and adjust the volume of sound that they can hear. Suppose you adjust it to a volume which you are able to detect but your mother says that she is unable to hear and asks you to increase the volume. If your mother asks you to stop after some point that means that difference of adjustment has been noticed by your mother. This minimal amount of change of volume between two stimuli that is being recognized by your mother is called a “difference threshold”.

Background of a stimulus also affects sensation. For example stars are present in the sky in day time and at night but are visible only after sunset or at nighttime because they can not be detected due to intense background of the daylight sun.

We all are also guided by factors of expectations and experiences. Experience of sensation is not simply a yes or no, present or absent mechanism. For example you are expecting a very close friend of yours to visit your home at 4 p.m. At 4 p.m. that friend reaches your house and pushes the doorbell button. Other members of your house do not notice it but you are able to notice that sound. It is primarily because of your expectation that you notice this second clearly while others do not notice it.

The minimum amount of physical energy needed to produce a sensory experience is called “absolute threshold”. We have several sense organs.

Sense Stimulus Sense organ Sensation
Sight Light waves Eye colors, patterns, textures
Hearing Sound waves Ear  noise, tones, music
Skin sensations External touch  Skin  touch, cold, warmth, pain
Smell  Volatile materials Nose  odors
Taste Soluble materials Tongue  sweet, salty, bitter


Vision is extremely important for all of us. Humans and animals with good vision have advantage in each and everything in life. We experience vision with the help of our eyes which function like a camera. The eye gathers and focuses light like a camera. Sir Isaac Newton, who in the seventeenth century discovered the laws of motion and gravity, also discovered that when white light passes through a prism it separates into a rainbow of color - the visible spectrum.

Color blindness: Not everyone sees colors in the same way. Some people are born with a color deficiency. Color blindness is the partial or total inability to distinguish colors. Most color blind people have trouble in distinguishing red from green.


Hearing is equally important for our daily life. It is a principal sensory modality for human communication. Sounds are created when actions cause objects to vibrate. When vibrating objects push the molecules of medium back and forth we can experience sound. Frequency refers to the number of cycles a wave completes in a given amount of time. It is usually expressed in cycles per second (CPS) or hertz (Hz). Sound cannot travel in a true vacuum (such as outer-space) because there is no medium there to move or vibrate.

Pitch: Pitch is the highness or lowness of a sound determined by the sound’s frequency. High frequencies produce high pitch and low frequencies produce low pitch.

Loudness: The loudness or physical intensity of a sound is determined by its amplitude. Sound waves with large amplitudes are experienced as loud and those with small amplitudes as soft. Loudness of sound is measured in units called decibels (dB).

Timbre: The quality of a sound wave’s complexity is its timbre. The sounds that we call noise contain many frequencies that are not systematically related to each other.

Sense of bodily orientation (vestibular sense)

It is the sense of bodily orientation with respect to gravity, especially how our heads are positioned, whether straight leaning, reclining or upside down. The vestibular sense also tells us when we are moving or how our motion is changing.

Sense of bodily position and the movement of body parts (Kinesthetic sense)

Kinesthetic sense is the sense of body position and the movement of body parts relative to each other. It is a sense that provides sensory feedback about motor activities of our body, for example how the hand moves to pick up the telephone when it rings.

Sense of smell (olfaction)

The sense of smell involves a sequence of bio-chemical activities that triggers neural impulses. Once activated these neural impulses convey odor information to the brain.

Sense of taste (gustation)

The taste receptor cells are gathered in the taste buds on the upper side of the tongue. The experience of sweetness or saltiness is affected by these taste buds. There are only four true or primary taste qualities: sweet, sour, bitter and saline. Taste sensitivity develops in infancy but decreases in old age. Taste receptors can be damaged by excessive use of alcohol, smoking, acids or hot foods but they are also replaced every few days and a permanent loss of taste is extremely rare.

Skin senses

The skin contains nerve endings that are stimulated by contact with external objects and it produces sensations of cold, warmth or pressure. The sensitivity to pressure is maximum on face, tongue and hands and it is less on our backs. Touch plays an important role in human relations and emotions.

Sense of pain

Pain is the body’s response to stimulation from noxious stimuli. Acute pain is reaction to sharp or sudden stimulation. The pain one feels in everyday life is also related to psycho-social and cultural habits. What “pain” a person experiences depend upon the meaning one attaches to pain and also on attention one receives from near and dear ones.