Each day consists of perception and cognition of the world around. It is made possible thanks to the five senses. A complex biological process is being conducted to transform the external information into electrical impulses recognized by the brain, which allows to interpret it. Traditional senses appear to be sight, hearing, taste, smell and touch. However, scientists discovered additional kinds of sensations that are usually being covered by the sense of touch such as temperature, pain, pressure, joint position, movement and muscle sense (Howard Hughes Medical Institute [HHMI], 1995).
In the past there was a distinction between “higher”, sight and hearing, and “lower” senses, taste, smell and touch. Sight and hearing allow to orientate in space, perceive distance and depth, communicate, whereas touch, taste and smell are mainly involved in contributing to security, well-being and pleasure (Köster, 2002).
Since antiquity, vision has been ranked first among senses. Dunn (2008) states that eyes contain a huge number of sensory receptors. They catalogue the light, color, size and shape of the objects around us. To the extent of perception and cognition of the world, brain associates visual memories with words and objects. Visual senses create a visual map of the world along with the body map that facilitates orientation and motion in the space. Much information is being processed without explicit awareness.
Depending on sensibility to the visual input, people can be divided into two groups. Some of them may occur to be bothered by brightness or high contrast and try to protect themselves by pulling shades or keeping lights low. Meanwhile others enjoy ‘bright, flooding light and lots of contrast because these visual experiences are stimulating and pleasing’ (Dunn, 2008).
The question of how human beings perceive colors have agitated the greatest minds of science. The fundamental discovery was made by Isaac Newton, who conducted experiments with prisms. It has leaked out that ordinary “white” light is really a mixture of lights of many different wavelengths, as seen in a rainbow. By reflecting certain wavelengths more than others, objects appear to be of a particular color (HHMI, 1997).
Later, the physician Thomas Young drew a conclusion that the retina could not possibly have a different receptor for each of the wavelengths, which span the entire continuum of colors from violet to red (HHMI, 1997). Therefore, a three-color code was proposed and it is still a well-known fact that any color except white can be produced by mixing others.
Sounds are all around us. According to Howes (2006), the ear is the primary organ through which the world is cognized. By detecting which ear hears it the loudest it is possible to figure out where sound is coming from. Memories of voices and sounds are being built the same way as with the sense of sight. Relying on loudness, volume or altitude, brain can interpret the information about the world around: distance, direction, material of which a certain object is made.
The ability to distinguish sounds allows human beings to understand each other, though it requires a creation of high-level mechanisms and maps based on acoustic patterns. It is amazing how everyone pronounce vowels and consonants in exactly different ways, and nonetheless people are able to recognize the similarities. Therefore, the above-mentioned neuronal maps play an important role in human voice recognition - the ability to recognize who is speaking as well as what is being said (HHMI, 1997).
Early in evolution, the two senses of taste and smell allowed single-celled organisms to survive by locating food or on the contrary by avoiding hazardous substances (HHMI, 1997).
The sense of taste is divided into the perception of saltiness, sweetness, sourness or bitterness, which emerges from neural activity within the central nervous system. Chemical structure of the food stimulates the taste receptors and the information of this perception is carried to the brain by the activity in peripheral taste nerves. It produces taste sensations, but also provides input that is critical for diverse somatic and visceral responses related to food ingestion and rejection (Beauchamp & Bartoshuk, 1997).
Therefore, feeding behavior of a human is being formed in accordance with the taste sensations. Nonetheless, dietary choices are being affected by other senses as well. A dish that is perfectly cooked may be rendered unappetizing due to foul odor, unexpected color or bad association with a particular experience (Yarmolinsky, Zuker, & Ryba, 2009).
In general, the main role in the control of feeding behavior is being played by senses of taste and smell, for they are bound to create perceptions of “flavor”. As long as taste buds can provide only four separate sensations, most of the flavor of food comes from its aroma, which ‘wafts up the nostrils to sensory cells in the nose and also reaches these cells through a passageway in the back of the mouth’ (HHMI, 1997).
Therefore, most of the food seems tasteless and insipid when the nose is blocked by a cold. It is essential to incorporate senses of taste and smell in order to let a broader picture emerge.
Since the beginning of time, mammals used their olfactory systems to survive. In this sense, human beings are less dependent. People are used to perceive the world mainly through eyes and ears. Yet, according to HHMI (1997), mothers can recognize their babies by smell, and newborns recognize their mothers in the same way.
Olfaction allows to obtain information about the surroundings which are contained in odors. The nose is an organ that can be characterized as sensitive and differentiating. It is said that the average human being can recognize some 10,000 separate odors (HHMI, 1997).
In olfaction and taste, the receptors retrieve all information about the quality of an object from the direct contact with the molecules. Olfaction and taste tend to be rather passive until a stimulus arrives. Olfaction is seldom the focus of attention and awareness of odors is the exception rather than the rule (Köster, 2002).
Throughout our lives our well-being is being under influence of the smells that surround us. Not only they affect our mood and health but also can retrieve emotion from the past. A lot of writers have created relying on this haunting quality of such memories from a long-forgotten scent or perfume (HHMI, 1997).
Touch begins with the activation of receptors embedded in the skin. Various receptors are sensitive to different aspects of skin stimulation, ranging from pressure and vibration to heating or cooling. Signals from these receptors are then conveyed to and processed in the brain. Signals from the receptors in the skin and their subsequent processing in the brain allow us to perceive the shape and texture of objects, motion across the skin, all of which are important in recognizing objects by touch and in manipulating them. To this effect, there are different types of receptors, even specialized ones in the skin and deep tissues for pressure and for light touch (Shepherd, 2007).
Dunn (2008) describes another important body sensation which is position-sense that keeps track of our body parts. Each movement triggers these receptors and they by-turn monitor the body in space. With additional input, it is easier to coordinate visual and movement sense input.
The main role of the five senses is to create an internal representation of the physical and chemical features of the outside world. The human organs of perception are constantly absorbing the information from the environment. A complex process of its interpreting enables accumulation of knowledge base, which allows to orientate in the surroundings more freely. According to Shepherd (2007), such physiological processes stimulate the larger brain functions which are perception, consciousness and memory.
The importance of the sensory systems consists of determination and discrimination of the signals, evaluation of its weakness or strength. Visual acuity or distinction of details as well as color discrimination, which consists of different wavelengths of light is what can be named in sight. Perception of sounds and its assessment according to altitude and loudness is involved in hearing. In smell it involves differentiation between various smells, meanwhile in taste - the basic tastes of salt, sweet, bitter and sour. The sense of touch is not only about the feel of different objects but also about orientation in space. Therefore, discrimination requires populations of sensory receptor cells that are capable to respond to various aspects of the stimuli (Shepherd, 2007).
The power of the five senses lies in its combination, which informs us about the structure of the world around through the non-conscious assessments of relative intensities, sizes, directions, hues and tones (Köster, 2002). Nonetheless, full knowledge can be acquired only if all the senses are working together.